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- DFG Forschungsgruppe 2757 / Lokale Selbstregelungen im Kontext schwacher Staatlichkeit in Antike und Moderne (LoSAM) (2)
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Stem cell therapy holds great promise for tissue regeneration and cancer treatment, although its efficacy is still inconclusive and requires further understanding and optimization of the procedures. Non-invasive cell tracking can provide an important opportunity to monitor in vivo cell distribution in living subjects. Here, using a combination of positron emission tomography (PET) and in vitro 2-deoxy-2-[18F]fluoro-D-glucose ([18F]FDG) direct cell labelling, the feasibility of engrafted stem cell monitoring was tested in multiple animal species. Human mesenchymal stem cells (MSCs) were incubated with phosphate-buffered saline containing [18F]FDG for in vitro cell radiolabelling. The pre-labelled MSCs were administrated via peripheral vein in a mouse (n=1), rats (n=4), rabbits (n=4) and non-human primates (n=3), via carotid artery in rats (n=4) and non-human primates (n=3), and via intra-myocardial injection in rats (n=5). PET imaging was started 10 min after cell administration using a dedicated small animal PET system for a mouse and rats. A clinical PET system was used for the imaging of rabbits and non-human primates. After MSC administration via peripheral vein, PET imaging revealed intense radiotracer signal from the lung in all tested animal species including mouse, rat, rabbit, and non-human primate, suggesting administrated MSCs were trapped in the lung tissue. Furthermore, the distribution of the PET signal significantly differed based on the route of cell administration. Administration via carotid artery showed the highest activity in the head, and intra-myocardial injection increased signal from the heart. In vitro [18F]FDG MSC pre-labelling for PET imaging is feasible and allows non-invasive visualization of initial cell distribution after different routes of cell administration in multiple animal models. Those results highlight the potential use of that imaging approach for the understanding and optimization of stem cell therapy in translational research.
Burns affect millions every year and a model to mimic the pathophysiology of such injuries in detail is required to better understand regeneration. The current gold standard for studying burn wounds are animal models, which are under criticism due to ethical considerations and a limited predictiveness. Here, we present a three-dimensional burn model, based on an open-source model, to monitor wound healing on the epidermal level. Skin equivalents were burned, using a preheated metal cylinder. The healing process was monitored regarding histomorphology, metabolic changes, inflammatory response and reepithelialization for 14 days. During this time, the wound size decreased from 25% to 5% of the model area and the inflammatory response (IL-1β, IL-6 and IL-8) showed a comparable course to wounding and healing in vivo. Additionally, the topical application of 5% dexpanthenol enhanced tissue morphology and the number of proliferative keratinocytes in the newly formed epidermis, but did not influence the overall reepithelialization rate. In summary, the model showed a comparable healing process to in vivo, and thus, offers the opportunity to better understand the physiology of thermal burn wound healing on the keratinocyte level.
Deafness, the most frequent sensory deficit in humans, is extremely heterogeneous with hundreds of genes involved. Clinical and genetic analyses of an extended consanguineous family with pre-lingual, moderate-to-profound autosomal recessive sensorineural hearing loss, allowed us to identify CLRN2, encoding a tetraspan protein, as a new deafness gene. Homozygosity mapping followed by exome sequencing identified a 14.96 Mb locus on chromosome 4p15.32p15.1 containing a likely pathogenic missense variant in CLRN2 (c.494C > A, NM_001079827.2) segregating with the disease. Using in vitro RNA splicing analysis, we show that the CLRN2 c.494C > A variant leads to two events: (1) the substitution of a highly conserved threonine (uncharged amino acid) to lysine (charged amino acid) at position 165, p.(Thr165Lys), and (2) aberrant splicing, with the retention of intron 2 resulting in a stop codon after 26 additional amino acids, p.(Gly146Lysfs*26). Expression studies and phenotyping of newly produced zebrafish and mouse models deficient for clarin 2 further confirm that clarin 2, expressed in the inner ear hair cells, is essential for normal organization and maintenance of the auditory hair bundles, and for hearing function. Together, our findings identify CLRN2 as a new deafness gene, which will impact future diagnosis and treatment for deaf patients.
Evolution has endowed the lung with exceptional design providing a large surface area for gas exchange area (ca. 100 m\(^{2}\)) in a relatively small tissue volume (ca. 6 L). This is possible due to a complex tissue architecture that has resulted in one of the most challenging organs to be recreated in the lab. The need for realistic and robust in vitro lung models becomes even more evident as causal therapies, especially for chronic respiratory diseases, are lacking. Here, we describe the Cyclic In VItro Cell-stretch (CIVIC) “breathing” lung bioreactor for pulmonary epithelial cells at the air-liquid interface (ALI) experiencing cyclic stretch while monitoring stretch-related parameters (amplitude, frequency, and membrane elastic modulus) under real-time conditions. The previously described biomimetic copolymeric BETA membrane (5 μm thick, bioactive, porous, and elastic) was attempted to be improved for even more biomimetic permeability, elasticity (elastic modulus and stretchability), and bioactivity by changing its chemical composition. This biphasic membrane supports both the initial formation of a tight monolayer of pulmonary epithelial cells (A549 and 16HBE14o\(^{-}\)) under submerged conditions and the subsequent cell-stretch experiments at the ALI without preconditioning of the membrane. The newly manufactured versions of the BETA membrane did not improve the characteristics of the previously determined optimum BETA membrane (9.35% PCL and 6.34% gelatin [w/v solvent]). Hence, the optimum BETA membrane was used to investigate quantitatively the role of physiologic cyclic mechanical stretch (10% linear stretch; 0.33 Hz: light exercise conditions) on size-dependent cellular uptake and transepithelial transport of nanoparticles (100 nm) and microparticles (1,000 nm) for alveolar epithelial cells (A549) under ALI conditions. Our results show that physiologic stretch enhances cellular uptake of 100 nm nanoparticles across the epithelial cell barrier, but the barrier becomes permeable for both nano- and micron-sized particles (100 and 1,000 nm). This suggests that currently used static in vitro assays may underestimate cellular uptake and transbarrier transport of nanoparticles in the lung.
Chronic respiratory diseases are among the leading causes of death worldwide, but only symptomatic therapies are available for terminal illness. This in part reflects a lack of biomimetic in vitro models that can imitate the complex environment and physiology of the lung. Here, a copolymeric membrane consisting of poly(ε‐)caprolactone and gelatin with tunable properties, resembling the main characteristics of the alveolar basement membrane is introduced. The thin bioinspired membrane (≤5 μm) is stretchable (up to 25% linear strain) with appropriate surface wettability and porosity for culturing lung epithelial cells under air–liquid interface conditions. The unique biphasic concept of this membrane provides optimum characteristics for initial cell growth (phase I) and then switch to biomimetic properties for cyclic cell‐stretch experiments (phase II). It is showed that physiologic cyclic mechanical stretch improves formation of F‐actin cytoskeleton filaments and tight junctions while non‐physiologic over‐stretch induces cell apoptosis, activates inflammatory response (IL‐8), and impairs epithelial barrier integrity. It is also demonstrated that cyclic physiologic stretch can enhance the cellular uptake of nanoparticles. Since this membrane offers considerable advantages over currently used membranes, it may lead the way to more biomimetic in vitro models of the lung for translation of in vitro response studies into clinical outcome.
A Calix[4]arene‐Based Cyclic Dinuclear Ruthenium Complex for Light‐Driven Catalytic Water Oxidation
(2021)
A cyclic dinuclear ruthenium(bda) (bda: 2,2’‐bipyridine‐6,6’‐dicarboxylate) complex equipped with oligo(ethylene glycol)‐functionalized axial calix[4]arene ligands has been synthesized for homogenous catalytic water oxidation. This novel Ru(bda) macrocycle showed significantly increased catalytic activity in chemical and photocatalytic water oxidation compared to the archetype mononuclear reference [Ru(bda)(pic)\(_2\)]. Kinetic investigations, including kinetic isotope effect studies, disclosed a unimolecular water nucleophilic attack mechanism of this novel dinuclear water oxidation catalyst (WOC) under the involvement of the second coordination sphere. Photocatalytic water oxidation with this cyclic dinuclear Ru complex using [Ru(bpy)\(_3\)]Cl\(_2\) as a standard photosensitizer revealed a turnover frequency of 15.5 s\(^{−1}\) and a turnover number of 460. This so far highest photocatalytic performance reported for a Ru(bda) complex underlines the potential of this water‐soluble WOC for artificial photosynthesis.
The cell—cell signaling gene CDH13 is associated with a wide spectrum of neuropsychiatric disorders, including attention-deficit/hyperactivity disorder (ADHD), autism, and major depression. CDH13 regulates axonal outgrowth and synapse formation, substantiating its relevance for neurodevelopmental processes. Several studies support the influence of CDH13 on personality traits, behavior, and executive functions. However, evidence for functional effects of common gene variation in the CDH13 gene in humans is sparse. Therefore, we tested for association of a functional intronic CDH13 SNP rs2199430 with ADHD in a sample of 998 adult patients and 884 healthy controls. The Big Five personality traits were assessed by the NEO-PI-R questionnaire. Assuming that altered neural correlates of working memory and cognitive response inhibition show genotype-dependent alterations, task performance and electroencephalographic event-related potentials were measured by n-back and continuous performance (Go/NoGo) tasks. The rs2199430 genotype was not associated with adult ADHD on the categorical diagnosis level. However, rs2199430 was significantly associated with agreeableness, with minor G allele homozygotes scoring lower than A allele carriers. Whereas task performance was not affected by genotype, a significant heterosis effect limited to the ADHD group was identified for the n-back task. Heterozygotes (AG) exhibited significantly higher N200 amplitudes during both the 1-back and 2-back condition in the central electrode position Cz. Consequently, the common genetic variation of CDH13 is associated with personality traits and impacts neural processing during working memory tasks. Thus, CDH13 might contribute to symptomatic core dysfunctions of social and cognitive impairment in ADHD.
The greatest problems faced during the 21st century is climate change which is a big threat to food security due to increasing number of people. The increase in extreme weather events, such as drought and heat, makes it difficult to cultivate conventional crops that are not stress tolerant. As a result, increasing irrigation of arable land leads to additional salinization of soils with plant-toxic sodium and chloride ions. Knowledge about the adaptation strategies of salt-tolerant plants to salt stress as well as detailed knowledge about the control of transpiration water loss of these plants are therefore important to guarantee productive agriculture in the future. In the present study, I have characterized salt sensitive and salt tolerant plant species at physiological, phenotypic and transcriptomic level under short (1x salt) and long-time (3x) saline growth conditions. Two approaches used for long-time saline growth conditions (i.e increasing saline conditions (3x salt) and constant high saline conditions (3x 200 mM salt) were successfully developed in the natural plant growth medium i.e soil. Salt sensitive plants, A. thaliana, were able to survive and successfully set seeds at the toxic concentrations on the increasing saline growth mediums, with minor changes in the phenotype. However, under constant high saline conditions they could not survive. This was due to keeping low potassium, and high salt ions (sodium and chloride) in the photosynthetic tissue i.e leaf. Similarly, high potassium and low salt ions in salt tolerant T. salsuginea on both saline environments were the key for survival of this plant species. Being salt tolerant, T. salsuginea always kept high potassium levels and low sodium (during 1x) and chloride levels (during both 1x and 3x) in the leaf tissue.
A strict control over transpirational water loss via stomata (formed by pair of guard cells) is important to maintain plant water balance. Aperture size of the stomata is regulated by the turgidity of the guard cells. More turgid the guard cells, bigger the apertures are and hence more transpiration. Under osmotic stress, the water loss is reduced which was evident in the salt sensitive A. thaliana plants under both short and long-time saline growth conditions. As the osmotic stress was only increased during long time saline growth conditions in T. salsuginea therefore, water loss was also decreased only under these saline conditions. Environmental CO2 assimilation also takes place via stomata in plants which then is used for photosynthesis. Stomatal apertures also influence CO2 assimilation. As the light absorbing photosynthetic pigments were more affected in A. thaliana, therefore photosynthetic activity of the whole plant was also reduced. Similarly, both short and long-time saline growth conditions also reduced the effective quantum yield of A. thaliana guard cells. Growth of the plant is dependent on energy which comes from photosynthesis. Reduced environmental CO2 assimilation would affect photosynthesis and hence growth, which was clearly observed in A. thaliana guard cells under long-time saline growth conditions.
Major differences in both guard cells types were observed in their chloride and potassium levels. Energy Dispersive X-Ray Analysis (EDXA) suggested strict control of chloride accumulation in T. salsuginea guard cells as the levels remain unchanged under all conditions. Similarly, use of sodium in place of potassium for osmotic adjustments seems to be dependent on Na+/K+ rations in both guard cell types. Increased salt ions and reduced potassium levels in A. thaliana guard cells posed negative effect on photochemistry which in turn increased ROS metabolism and reduced energy related pathways at transcriptomic level in this plant species. Moreover, photosynthesis was strongly affected in A. thaliana guard cells both at transcriptomic and physiological levels. Similarly, global phytohormones induced changes were more evident in A. thaliana guard cells especially on 3x salt medium. Among all phytohormones, genes under the control of auxin were more differentially expressed in A. thaliana guard cells which suggests wide changes in growth and development in this plant species under salinity.
Phytohormone, ABA is vital for closing the stomata under abiotic stress conditions. Increased levels of ABA during saline conditions led to efflux of potassium and counter anions (chloride, malate, nitrate) from the guard cells which caused the outward flow of water and hence reduction in turgor pressure. Reduced turgor pressure led to reduced water loss and CO2 assimilation especially in A. thaliana. Guard cells of both plant species synthesized ABA during saline conditions which was reflected from transcriptomic data and ABA quantification in the guard cells. ABA induced signaling in both plant species varied at the ABA receptor (PYL/PYR) levels where totally contrasting responses were observed. PYL2, PYL8 and PYL9 were specific to A. thaliana, furthermore, PYL2 was found to be differentially expressed only under 3x salt growth conditions thus suggesting its role during long term salt stress in this plant species. Protein phosphatases, which negatively regulate ABA signaling on one hand and act as ABA sensor on the other hand were found to be more differentially expressed in A. thaliana than T. salsuginea guard cells, which suggests their diverse role in both plant species under saline conditions. Differential expression of more ABA signaling players in long time saline conditions was prominent which could be because of darkness, as it is well known that rapid closure of stomata under dark conditions require ABA signaling. Moreover, representation of these components in dark also suggests that plants become more sensitive to dark under saline conditions which is also evident from the transpiration rates.
Altogether, increased salt ions in A. thaliana guard cells and leaves led to pigment degradation and ABA induced reduction in transpiration which in turn influenced its growth. In contrast, T. salsuginea is the salt excluder and therefore keeps low levels of salt ions especially the chloride both in leaves and guard cells which mildly affects its growth. Guard cells of A. thaliana encounter severe energy problems at physiological and transcriptomic level. Main differences in the ABA signalling between both plant species were observed at the ABA receptor level.
Summary
Bees, like many other organisms, evolved an endogenous circadian clock, which enables them to foresee daily environmental changes and exactly time foraging flights to periods of floral resource availability. The social lifestyle of a honey bee colony has been shown to influence circadian behavior in nurse bees, which do not exhibit rhythmic behavior when they are nursing. On the other hand, forager bees display strong circadian rhythms. Solitary bees, like the mason bee, do not nurse their offspring and do not live in hive communities, but face the same daily environmental changes as honey bees. Besides their lifestyle mason and honey bees differ in their development and life history, because mason bees overwinter after eclosion as adults in their cocoons until they emerge in spring. Honey bees do not undergo diapause and have a relatively short development of a few weeks until they emerge. In my thesis, I present a comparison of the circadian clock of social honey bees (Apis mellifera) and solitary mason bees (Osmia bicornis and Osmia cornuta) on the neuroanatomical level and behavioral output level.
I firstly characterized in detail the localization of the circadian clock in the bee brain via the expression pattern of two clock components, namely the clock protein PERIOD (PER) and the neuropeptide Pigment Dispersing Factor (PDF), in the brain of honey bee and mason bee. PER is localized in lateral neuron clusters (which we called lateral neurons 1 and 2: LN1 and LN2) and dorsal neuron clusters (we called dorsal lateral neurons and dorsal neurons: DLN, DN), many glia cells and photoreceptor cells. This expression pattern is similar to the one in other insect species and indicates a common ground plan of clock cells among insects. In the LN2 neuron cluster with cell bodies located in the lateral brain, PER is co-expressed with PDF. These cells build a complex arborization network throughout the brain and provide the perfect structure to convey time information to brain centers, where complex behavior, e.g. sun-compass orientation and time memory, is controlled. The PDF arborizations centralize in a dense network (we named it anterio-lobular PDF hub: ALO) which is located in front of the lobula. In other insects, this fiber center is associated with the medulla (accessory medulla: AME). Few PDF cells build the ALO already in very early larval development and the cell number and complexity of the network grows throughout honey bee development. Thereby, dorsal regions are innervated first by PDF fibers and, in late larval development, the fibers grow laterally to the optic lobe and central brain. The overall expression pattern of PER and PDF are similar in adult social and solitary bees, but I found a few differences in the PDF network density in the posterior protocerebrum and the lamina, which may be associated with evolution of sociality in bees.
Secondly, I monitored activity rhythms, for which I developed and established a device to monitor locomotor activity rhythms of individual honey bees with contact to a mini colony in the laboratory. This revealed new aspects of social synchronization and survival of young bees with indirect social contact to the mini colony (no trophalaxis was possible). For mason bees, I established a method to monitor emergence and locomotor activity rhythms and I could show that circadian emergence rhythms are entrainable by daily temperature cycles. Furthermore, I present the first locomotor activity rhythms of solitary bees, which show strong circadian rhythms in their behavior right after emergence. Honey bees needed several days to develop circadian locomotor rhythms in my experiments. I hypothesized that honey bees do not emerge with a fully matured circadian system in the hive, while solitary bees, without the protection of a colony, would need a fully matured circadian clock right away after emergence. Several indices in published work and preliminary studies support my hypothesis and future studies on PDF expression in different developmental stages in solitary bees may provide hard evidence.
A Comprehensive Review on the Interplay between Neisseria spp. and Host Sphingolipid Metabolites
(2021)
Sphingolipids represent a class of structural related lipids involved in membrane biology and various cellular processes including cell growth, apoptosis, inflammation and migration. Over the past decade, sphingolipids have become the focus of intensive studies regarding their involvement in infectious diseases. Pathogens can manipulate the sphingolipid metabolism resulting in cell membrane reorganization and receptor recruitment to facilitate their entry. They may recruit specific host sphingolipid metabolites to establish a favorable niche for intracellular survival and proliferation. In contrast, some sphingolipid metabolites can also act as a first line defense against bacteria based on their antimicrobial activity. In this review, we will focus on the strategies employed by pathogenic Neisseria spp. to modulate the sphingolipid metabolism and hijack the sphingolipid balance in the host to promote cellular colonization, invasion and intracellular survival. Novel techniques and innovative approaches will be highlighted that allow imaging of sphingolipid derivatives in the host cell as well as in the pathogen.
The HIV-1 Vif protein is essential for viral fitness and pathogenicity. Vif decreases expression of cellular restriction factors APOBEC3G (A3G), A3F, A3D and A3H, which inhibit HIV-1 replication by inducing hypermutation during reverse transcription. Vif counteracts A3G at several levels (transcription, translation, and protein degradation) that altogether reduce the levels of A3G in cells and prevent its incorporation into viral particles. How Vif affects A3G translation remains unclear. Here, we uncovered the importance of a short conserved uORF (upstream ORF) located within two critical stem-loop structures of the 5′ untranslated region (5′-UTR) of A3G mRNA for this process. A3G translation occurs through a combination of leaky scanning and translation re-initiation and the presence of an intact uORF decreases the extent of global A3G translation under normal conditions. Interestingly, the uORF is also absolutely required for Vif-mediated translation inhibition and redirection of A3G mRNA into stress granules. Overall, we discovered that A3G translation is regulated by a small uORF conserved in the human population and that Vif uses this specific feature to repress its translation.
We derive a multi-species BGK model with velocity-dependent collision frequency for a non-reactive, multi-component gas mixture. The model is derived by minimizing a weighted entropy under the constraint that the number of particles of each species, total momentum, and total energy are conserved. We prove that this minimization problem admits a unique solution for very general collision frequencies. Moreover, we prove that the model satisfies an H-Theorem and characterize the form of equilibrium.
Semi-arid tree covers, in both high and coppice growth forms, play an essential role in protecting water and soil resources and provides multiple ecosystem services across fragile ecosystems. Thus, they require continuous inventories. Quantification of forest structure in these tree covers provides important measures for their management and biodiversity conservation. We present a framework, based on consumer-grade UAV photogrammetry, to separately estimate primary variables of tree height (H) and crown area (A) across diverse coppice and high stands dominated by Quercus brantii Lindl. along the latitudinal gradient of Zagros mountains of western Iran. Then, multivariate linear regressions were parametrized with H and A to estimate the diameter at breast height (DBH) of high trees because of its importance to accelerate the existing practical DBH inventories across Zagros Forests. The estimated variables were finally applied to a model tree aboveground biomass (AGB) for both vegetative growth forms by local allometric equations and Random Forest models. In each step, the estimated variables were evaluated against the field reference values, indicating practically high accuracies reaching root mean square error (RMSE) of 0.68 m and 4.74 cm for H and DBH, as well as relative RMSE < 10% for AGB estimates. The results generally suggest an effective framework for single tree-based attribute estimation over mountainous, semi-arid coppice, and high stands.
Recovery during yesterday’s leisure time is beneficial for morning recovery, and morning recovery fosters employees’ work engagement, a positive, motivational state associated with job performance. We extended existing research by assuming that both, morning recovery (considered a resource) and anticipated leisure time (considered an anticipated resource gain), relate to work engagement. Anticipated leisure time comprises two constructs: general anticipation of leisure time, which refers to employees’ cognitive evaluation of their entire upcoming leisure time, and pleasant anticipation of a planned leisure activity, which describes a positive affective reaction because of one specific, upcoming leisure activity. We suggested that employees with high pleasant anticipation generate more thoughts of a planned leisure activity (ToPLA), which may distract them from their work, reducing their work engagement. A diary study over five days showed that morning recovery and general anticipation of leisure time were positively related to work engagement. Furthermore, employees with higher pleasant anticipation of a planned leisure activity reported more ToPLA. In contrast to our expectations, neither pleasant anticipation nor ToPLA was related to work engagement. In sum, this study introduced anticipated leisure time as a novel antecedent of work engagement and demonstrated that anticipated resource gains are important for high work engagement.
The parasite Trypanosoma brucei periodically changes the expression of protective variant surface glycoproteins (VSGs) to evade its host's immune sys-tem in a process known as antigenic variation. One route to change VSG expres-sion is the transcriptional activation of a previously silent VSG expression site (ES), a subtelomeric region containing the VSG genes. Homologous recombination of a different VSG from a large reservoir into the active ES represents another route. The conserved histone methyltransferase DOT1B is involved in transcriptional silencing of inactive ES and influences ES switching kinetics. The molecular machin-ery that enables DOT1B to execute these regulatory functions remains elusive, however. To better understand DOT1B-mediated regulatory processes, we purified DOT1B-associated proteins using complementary biochemical approaches. We iden-tified several novel DOT1B interactors. One of these was the RNase H2 complex, previously shown to resolve RNA-DNA hybrids, maintain genome integrity, and play a role in antigenic variation. Our study revealed that DOT1B depletion results in an increase in RNA-DNA hybrids, accumulation of DNA damage, and ES switch-ing events. Surprisingly, a similar pattern of VSG deregulation was observed in RNase H2 mutants. We propose that both proteins act together in resolving R-loops to ensure genome integrity and contribute to the tightly regulated process of anti-genic variation.
Arapaima gigas is one of the largest freshwater fish species of high ecological and economic importance. Overfishing and habitat destruction are severe threats to the remaining wild populations. By incorporating a chromosomal Hi-C contact map, we improved the arapaima genome assembly to chromosome-level, revealing an unexpected high degree of chromosome rearrangements during evolution of the bonytongues (Osteoglossiformes). Combining this new assembly with pool-sequencing of male and female genomes, we identified id2bbY, a duplicated copy of the inhibitor of DNA binding 2b (id2b) gene on the Y chromosome as candidate male sex-determining gene. A PCR-test for id2bbY was developed, demonstrating that this gene is a reliable male-specific marker for genotyping. Expression analyses showed that this gene is expressed in juvenile male gonads. Its paralog, id2ba, exhibits a male-biased expression in immature gonads. Transcriptome analyses and protein structure predictions confirm id2bbY as a prime candidate for the master sex-determiner. Acting through the TGF beta signaling pathway, id2bbY from arapaima would provide the first evidence for a link of this family of transcriptional regulators to sex determination. Our study broadens our current understanding about the evolution of sex determination genetic networks and provide a tool for improving arapaima aquaculture for commercial and conservation purposes.
The implantation of any foreign material into the body automatically starts an immune reaction that serves as the first, mandatory step to regenerate tissue. The course of this initial immune reaction decides on the fate of the implant: either the biomaterial will be integrated into the host tissue to subsequently fulfill its intended function (e.g., tissue regeneration), or it will be repelled by fibrous encapsulation that determines the implant failure. Especially neutrophils and macrophages play major roles during this inflammatory response and hence mainly decide on the biomaterial's fate. For clinically relevant tissue engineering approaches, biomaterials may be designed in shape and morphology as well as in their surface functionality to improve the healing outcome, but also to trigger stem cell responses during the subsequent tissue regeneration phase.
The main focus of this thesis was to unravel the influence of scaffold characteristics, including scaffold morphology and surface functionality, on primary human innate immune cells (neutrophils and macrophages) and human mesenchymal stromal cells (hMSCs) to assess their in vitro immune response and tissue regeneration capacity, respectively. The fiber-based constructs were produced either via melt electrowriting (MEW), when the precise control over scaffold morphology was required, or via solution electrospinning (ES), when the scaffold design could be neglected. All the fiber-based scaffolds used throughout this thesis were composed of the polymer poly(ε caprolactone) (PCL).
A novel strategy to model and alleviate the first direct cell contact of the immune system with a peptide-bioactived fibrous material was presented in chapter 3 by treating the material with human neutrophil elastase (HNE) to imitate the neutrophil attack. The main focus of this study was put on the effect of HNE towards an RGDS-based peptide that was immobilized on the surface of a fibrous material to improve subsequent L929 cell adhesion. The elastase efficiently degraded the peptide-functionality, as evidenced by a decreased L929 cell adhesion, since the peptide integrated a specific HNE-cleavage site (AAPV-motif). A sacrificial hydrogel coating based on primary oxidized hyaluronic acid (proxHA), which dissolved within a few days after the neutrophil attack, provided an optimal protection of the peptide-bioactivated fibrous mesh, i.e, the hydrogel alleviated the neutrophil attack and largely ensured the biomaterial's integrity. Thus, according to these results, a means to protect the biomaterial is required to overcome the neutrophil attack.
Chapter 4 was based on the advancement of melt electrowriting (MEW) to improve the printing resolution of MEW scaffolds in terms of minimal inter-fiber distances and a concomitant high stacking precision. Initially, to gain a better MEW understanding, the influence of several parameters, including spinneret diameter, applied pressure, and collector velocity on mechanical properties, crystallinity, fiber diameter and fiber surface morphology was analyzed. Afterward, innovative MEW designs (e.g., box-, triangle-, round , and wall-shaped scaffolds) have been established by pushing the printing parameters to their physical limits. Further, the inter-fiber distance within a standardized box-structured scaffold was successfully reduced to 40 µm, while simultaneously a high stacking precision was maintained. In collaboration with a co-worker of my department (Tina Tylek, who performed all cell-based experiments in this study), these novel MEW scaffolds have been proven to facilitate human monocyte-derived macrophage polarization towards the regenerative M2 type in an elongation-driven manner with a more pronounced effect with decreasing pore sizes.
Finally, a pro-adipogenic platform for hMSCs was developed in chapter 5 using MEW scaffolds with immobilized, complex ECM proteins (e.g., human decellularized adipose tissue (DAT), laminin (LN), and fibronectin (FN)) to test for the adipogenic differentiation potential in vitro. Within this thesis, a special short-term adipogenic induction regime enabled to more thoroughly assess the intrinsic pro-adipogenic capacity of the composite biomaterials and prevented any possible masking by the commonly used long-term application of adipogenic differentiation reagents. The scaffolds with incorporated DAT consistently showed the highest adipogenic outcome and hence provided an adipo-inductive microenvironment for hMSCs, which holds great promise for applications in soft tissue regeneration.
Future studies should combine all three addressed projects in a more in vivo-related manner, comprising a co-cultivation setup of neutrophils, macrophages, and MSCs. The MEW-scaffold, particularly due to its ability to combine surface functionality and adjustable morphology, has been proven to be a successful approach for wound healing and paves the way for subsequent tissue regeneration.
A General Synthetic Route to NHC‐Phosphinidenes: NHC‐mediated Dehydrogenation of Primary Phosphines
(2021)
The dehydrocoupling of primary phosphines with N-heterocyclic carbenes (NHCs) to yield NHC-phosphinidenes is reported. The reaction of two equivalents of the NHCs Me\(_2\)Im (1,3-dimethylimidazolin-2-ylidene), Me\(_4\)Im (1,3,4,5-tetramethylimidazolin-2-ylidene), iPr\(_2\)Im (1,3-di-iso-propylimidazolin-2-ylidene) and Mes\(_2\)Im (2,4,6-trimethylphenylimidazolin-2-ylidene) with PhPH\(_2\) and MesPH\(_2\) led to the NHC stabilized phosphinidenes (NHC)PAr: (iPr\(_2\)Im)PPh (1), (Mes\(_2\)Im)PPh (2), (Me\(_4\)Im)PPh (3), (Mes\(_2\)Im)PMes (4), (Me\(_2\)Im)PMes (5), (Me\(_4\)Im)PMes (6) and (iPr\(_2\)Im)PMes (7). The reaction of tBuPH\(_2\) with two equivalents of the NHCs afforded the corresponding NHC stabilized parent phosphinidenes (NHC)PH: (iPr\(_2\)Im)PH (8), (Mes\(_2\)Im)PH (9) and (Me\(_4\)Im)PH (10). Reaction of 1 with oxygen and sulfur led to isolation of iPr\(_2\)Im-P(O)\(_2\)Ph (11) and iPr\(_2\)Im-P(S)\(_2\)Ph (12), whereas the reaction with elemental selenium and tellurium gave (NHC)PPh cleavage with formation of (iPr\(_2\)Im)Se (13), iPr\(_2\)ImTe (14) and different cyclo-oligophosphines. Furthermore, the complexes [{(iPr\(_2\)Im)PPh}W(CO)\(_5\)] (15), [Co(CO)\(_2\)(NO){(iPr\(_2\)Im)PPh}] (16) and [(η\(^5\)-C\(_5\)Me\(_2\))Co(η\(^2\)-C\(_2\)H\(_4\)){(iPr\(_2\)Im)PPh}] (17) have been prepared starting from 1 and a suitable transition metal complex precursor. The complexes 16 and 17 decompose in solution upon heating to ca. 80 °C to yield the NHC complexes [Co(iPr\(_2\)Im)(CO)\(_2\)(NO)] and [(η\(^5\)-C\(_5\)Me\(_5\))Co(iPr\(_2\)Im)(η\(^2\)-C\(_2\)H\(_4\))] with formation of cyclo-oligophosphines. The reaction of 1 with [Ni(COD)\(_2\)] afforded the diphosphene complex [Ni(iPr\(_2\)Im)\(_2\)(trans-PhP=PPh)] 18.
The Gram-negative rod-shaped bacterium Pseudomonas aeruginosa is not only a major cause of nosocomial infections but also serves as a model species of bacterial RNA biology. While its transcriptome architecture and posttranscriptional regulation through the RNA-binding proteins Hfq, RsmA, and RsmN have been studied in detail, global information about stable RNA-protein complexes in this human pathogen is currently lacking. Here, we implement gradient profiling by sequencing (Grad-seq) in exponentially growing P. aeruginosa cells to comprehensively predict RNA and protein complexes, based on glycerol gradient sedimentation profiles of >73% of all transcripts and ∼40% of all proteins. As to benchmarking, our global profiles readily reported complexes of stable RNAs of P. aeruginosa, including 6S RNA with RNA polymerase and associated product RNAs (pRNAs). We observe specific clusters of noncoding RNAs, which correlate with Hfq and RsmA/N, and provide a first hint that P. aeruginosa expresses a ProQ-like FinO domain-containing RNA-binding protein. To understand how biological stress may perturb cellular RNA/protein complexes, we performed Grad-seq after infection by the bacteriophage ΦKZ. This model phage, which has a well-defined transcription profile during host takeover, displayed efficient translational utilization of phage mRNAs and tRNAs, as evident from their increased cosedimentation with ribosomal subunits. Additionally, Grad-seq experimentally determines previously overlooked phage-encoded noncoding RNAs. Taken together, the Pseudomonas protein and RNA complex data provided here will pave the way to a better understanding of RNA-protein interactions during viral predation of the bacterial cell.
IMPORTANCE Stable complexes by cellular proteins and RNA molecules lie at the heart of gene regulation and physiology in any bacterium of interest. It is therefore crucial to globally determine these complexes in order to identify and characterize new molecular players and regulation mechanisms. Pseudomonads harbor some of the largest genomes known in bacteria, encoding ∼5,500 different proteins. Here, we provide a first glimpse on which proteins and cellular transcripts form stable complexes in the human pathogen Pseudomonas aeruginosa. We additionally performed this analysis with bacteria subjected to the important and frequently encountered biological stress of a bacteriophage infection. We identified several molecules with established roles in a variety of cellular pathways, which were affected by the phage and can now be explored for their role during phage infection. Most importantly, we observed strong colocalization of phage transcripts and host ribosomes, indicating the existence of specialized translation mechanisms during phage infection. All data are publicly available in an interactive and easy to use browser.