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Institute
- Neurologische Klinik und Poliklinik (36) (remove)
Sonstige beteiligte Institutionen
Aging is known to be a risk factor for structural abnormalities and functional decline in the nervous system. Characterizing age-related changes is important to identify putative pathways to overcome deleterious effects and improve life quality for the elderly. In this study, the peripheral nervous system of 24-month-old aged C57BL/6 mice has been investigated and compared to 12-month-old adult mice. Aged mice showed pathological alterations in their peripheral nerves similar to nerve biopsies from elderly human individuals, with nerve fibers showing demyelination and axonal damage. Such changes were lacking in nerves of adult 12-month-old mice and adult, non-aged humans. Moreover, neuromuscular junctions of 24-month-old mice showed increased denervation compared to adult mice. These alterations were accompanied by elevated numbers of macrophages in the peripheral nerves of aged mice. The neuroinflammatory conditions were associated with impaired myelin integrity and with a decline of nerve conduction properties and muscle strength in aged mice.
To determine the pathological impact of macrophages in the aging mice, macrophage depletion was performed in mice by oral administration of CSF-1R specific kinase (c-FMS) inhibitor PLX5622 (300 mg/kg body weight), which reduced the number of macrophages in the peripheral nerves by 70%. The treated mice showed attenuated demyelination, less muscle denervation and preserved muscle strength. This indicates that macrophage-driven inflammation in the peripheral nerves is partially responsible for the age-related neuropathy in mice.
Based on previous observations that systemic inflammation can accelerate disease progression in mouse models of neurodegenerative diseases, it was hypothesized that systemic inflammation can exacerbate the peripheral neuropathy found in aged mice. To investigate this hypothesis, aged C57BL/6 mice were intraperitoneally injected with a single dose of lipopolysaccharide (LPS; 500 μg/kg body weight) to induce systemic inflammation by mimicking bacterial infection, mostly via activation of Toll-like receptors (TLRs). Altered endoneurial macrophage activation, highlighted by Trem2 downregulation, was found in LPS injected aged mice one month after injection. This was accompanied by a so far rarely observed form of axonal perturbation, i.e., the occurrence of “dark axons” characterized by a damaged cytoskeleton and an increased overall electron density of the axoplasm. At the same time, however, LPS injection reduced demyelination and muscle denervation in aged mice. Interestingly, TREM2 deficiency in aged mice led to similar changes to LPS injection. This suggests that LPS injection likely mitigates aging-related demyelination and muscle denervation via Trem2 downregulation.
Taken together, this study reveals the role of macrophage-driven inflammation as a pathogenic mediator in age-related peripheral neuropathy, and that targeting macrophages might be an option to mitigate peripheral neuropathies in aging individuals. Furthermore, this study shows that systemic inflammation may be an ambivalent modifier of age-related nerve damage, leading to a distinct type of axonal perturbation, but in addition to functionally counteracting, dampened demyelination and muscle denervation. Translationally, it is plausible to assume that tipping the balance of macrophage polarization to one direction or the other may determine the functional outcome in the aging peripheral nervous system of the elderly.
The present cumulative dissertation summarizes three clinical studies, which examine
subgroups of patients within the fibromyalgia syndrome (FMS). FMS entails chronic pain and
associated symptoms, and its pathophysiology is incompletely understood (1). Previous studies
show that there is a subgroup of patients with FMS with objective histological pathology of the
small nerve fibers of the peripheral nervous system (PNS). Another subgroup of FMS patients
does not show any signs of pathological changes of the small nerve fibers. The aim of this
dissertation was to compare FMS patients with healthy controls, and these two FMS subgroups
for differences in the central nervous system (CNS) in order to explore possible interactions
between PNS and the CNS. Regarding the CNS, differences of FMS patients with healthy
controls have already been found in studies with small sample sizes, but no subgroups have yet
been identified. Another aim of this thesis was to test whether the subgroups show a different
response to different classes of pain medication. The methods used in this thesis are structural
and functional magnetic resonance imaging (MRI), magnetic resonance diffusion imaging and
magnetic resonance spectroscopy. For the evaluation of clinical symptoms, we used
standardized questionnaires. The subgroups with and without pathologies of the PNS were
determined by skin biopsies of the right thigh and lower leg based on the intraepidermal nerve
fiber density (IENFD) of the small nerve fibers.
1) In the first MRI study, 43 female patients with the diagnosis of FMS and 40 healthy
control subjects, matched in age and body mass index, were examined with different MRI
sequences. Cortical thickness was investigated by structural T1 imaging, white matter integrity
by diffusion tensor imaging and functional connectivity within neuronal networks by functional
resting state MRI. Compared to the controls, FMS patients had a lower cortical volume in
bilateral frontotemporoparietal regions and the left insula, but a higher cortical volume in the
left pericalcarine cortex. Compared to the subgroup without PNS pathology, the subgroup with
PNS pathology had lower cortical volume in both pericalcarine cortices. Diffusion tensor
imaging revealed an increased fractional anisotropy (FA) of FMS patients in corticospinal
pathways such as the corona radiata, but also in regions of the limbic systems such as the fornix
and cingulum. Subgroup comparison again revealed lower mean FA values of the posterior
thalamic radiation and the posterior limb of the left internal capsule in the subgroup with PNS
pathology. In the functional connectivity analysis FMS patients, compared to controls, showed
a hypoconnectivity between the right median frontal gyrus and the posterior cerebellum and
the right crus cerebellum, respectively. In the subgroup comparisons, the subgroup with PNS
pathology showed a hyperconnectivity between both inferior frontal gyri, the right posterior
parietal cortex and the right angular gyrus. In summary, these results show that differences in
brain morphology and functional connectivity exist between FMS patients with and without
PNS pathology. These differences were not associated with symptom duration or severity and,
in some cases, have not yet been described in the context of FMS. The differences in brain
morphology and connectivity between subgroups could also lead to a differential response to
treatment with centrally acting drugs. Further imaging studies with FMS patients should take
into account this heterogeneity of FMS patient cohorts.
2) Following the results from the first MRI study, drug therapies of FMS patients and
their treatment response were compared between PNS subgroups. As there is no licensed drug
for FMS in Europe, the German S3 guideline recommends amitriptyline, duloxetine and
pregabalin for temporary use. In order to examine the current drug use in FMS patients in
Germany on a cross-sectional basis, 156 patients with FMS were systematically interviewed.
The drugs most frequently used to treat pain in FMS were non-steroidal anti-inflammatory
drugs (NSAIDs) (28.9%), metamizole (15.4%) and amitriptyline (8.8%). Pain relief assessed by
patients on a numerical rating scale from 0-10 averaged 2.2 points for NSAIDs, 2.0 for
metamizole and 1.5 for amitriptyline. Drugs that were discontinued for lack of efficacy and not
for side effects were acetaminophen (100%), flupirtine (91.7%), selective serotonin reuptake
inhibitors (81.8%), NSAIDs (83.7%) and weak opioids (74.1%). Patients were divided into
subgroups with and without PNS pathology as determined by skin biopsies. We found no
differences in drug use and effect between the subgroups. Taken together, these results show
that many FMS patients take medication that is not in accordance with the guidelines. The
reduction of symptoms was best achieved with metamizole and NSAIDs. Further longitudinal
studies on medication in FMS are necessary to obtain clearer treatment recommendations.
3) Derived from previous pharmacological and imaging studies (with smaller case
numbers), there is a hypothesis in the FMS literature that hyperreactivity of the insular cortex
may have an impact on FMS. The hyperreactivity seems to be due to an increased concentration
of the excitatory neurotransmitter glutamate in the insular cortex of FMS patients. The
hypothesis is supported by magnetic resonance spectroscopy studies with small number of
cases, as well as results from pharmacological studies with glutamate-inhibiting medication.
Studies from animal models have also shown that an artificially induced increase in glutamate
in the insular cortex can lead to reduced skin innervation. Therefore, the aim of this study was
to compare glutamate and GABA concentrations in the insular cortex of FMS patients with
those of healthy controls using magnetic resonance imaging. There was no significant
difference of both neurotransmitters between the groups. In addition, there was no correlation
between the neurotransmitter concentrations and the severity of clinical symptoms. There
were also no differences in neurotransmitter concentrations between the subgroups with and
without PNS pathology. In conclusion, our study could not show any evidence of a correlation
of glutamate and GABA concentrations with the symptoms of FMS or the pathogenesis of
subgroups with PNS pathologies.
We examined 143 patients suffering from FMS, a syndrome characterized by chronic widespread pain, sleep disturbances, and fatigue. Etiology and pathophysiology of FMS are scarcely understood. In recent years abnormalities of small Aδ- and C-nerve fibers have been found in subgroups of FMS patients. It is yet unclear how such SFP is caused in FMS patients and how it contributes to FMS symptoms.
We used CCM to analyze corneal small nerve fibers and associated LC, comparing FMS patients’ results to those from 65 healthy controls and 41 disease controls suffering from SFN. We, further, assessed expression levels of mRNA and miRNA in keratinocytes taken from skin punch biopsies of FMS patients and healthy controls kept as monocellular cell cultures. A screening was performed using NGS in a small cohort of 12 FMS patients and 5 healthy controls. Results were validated in larger cohorts by qRT-PCR.
As in previous studies IENFD and CNFD were reduced in a subgroup of FMS patients. We found identical LC densities in FMS patients, healthy controls, and SFN patients. The subpopulation of dLCfiber contact in FMS and SFN patients was lower than in healthy controls. Our RNA expression analysis revealed one mRNA that was expressed higher in FMS patients than in controls: PRSS21.
We conclude that reduced neurotrophic signaling of LC may contribute to SFP in the cornea. Epidermal PRSS21 expression and dLCfiber contact density are promising biomarker candidates for FMS diagnosis.
Previous studies by our group revealed that chronic low grade inflammation implicating phagocytosing macrophages is a highly relevant mechanism in the pathogenesis of Charcot-Marie-Tooth disease. The lack of CSF-1, the primary regulator of macrophage function and survival, led to a robust and persistent amelioration of the phenotype in two authentic mouse models of CMT. Moreover, a close contact between CSF-1 producing fibroblasts and endoneurial macrophages carrying CSF-1R has been confirmed in nerve biopsies of CMT patients, further supporting the clinical significance of this pathway. In the current study we treated 3 distinct mouse models of CMT1: the PMP22tg mice as a model for CMT1A, the P0+/- mice as a model for CMT1B and the Cx32def mice as a model for CMT1X, with a CSF-1R specific kinase (c-FMS) inhibitor (800-1200 mg PLX5622/ kg chow) according to different treatment regimes mimicking an ideal early onset treatment, a late onset treatment and the withdrawal of the drug. Using the above mentioned doses of PLX5622, we documented a dramatic decrease in macrophage numbers in the PNS of all 3 myelin mutants, except for the quadriceps nerve of Cx32def mice. Fibroblast numbers remained unchanged in treated animals. Surprisingly, in spite of the decrease in the number of detrimental macrophages we could not detect an unequivocal phenotypic improvement. CMAP amplitudes were reduced in both wild type and myelin mutant mice treated with CSF-1R inhibitor in comparison to untreated littermates. Corresponding to the electrophysiological findings, the axon number and the percentage of large diameter axons were reduced in the quadriceps nerve of treated P0+/- and Cx32def mice. By contrast we observed a higher number of fully myelinated axons, in parallel with a decrease in the percentage of demyelinated (and hypermyelinated in PMP22tg mice) fibers in the ventral roots of P0+/- mice treated with CSF-1R inhibitor from 3 months up to 6 months of age and PMP22tg animals treated from 9 months up to 15 months of age. Our results indicate that CSF-1R inhibitor has the potential to improve the demyelinating phenotype of at least two models of CMT1. Nevertheless, further studies are necessary (for example with lower doses of the inhibitor) to minimize or even eliminate the putative neurotoxic effect we observed with high dose treatment conditions.
Lewy bodies and Lewy neurites are neuropathological hallmarks of Parkinson’s disease (PD). These depositions in the brain mostly consist of aggregated α-synuclein (α-syn) phosphorylated at Ser129. A number of studies reported detection of phosphorylated α-syn (p-α-syn) in the dermal nerve fibers in Parkinson’s disease. The objective of this study was to investigate whether pathological α-syn accumulations detected in the skin represent aggregated protein. A number of methods aimed at detecting α-syn oligomers and aggregates were first tested and optimized on the brain samples in PD and normal control. These methods included proximity ligation assay (PLA), PET-blot, immunohistochemical (IHC) stains with α-syn aggregate (5G4) or oligomer specific (ASyO5) antibodies and a stain against native α-syn (syn211) after proteinase K (PK) digestion. Subsequently, the most specific methods (stains with 5G4, ASyO5 and syn211 after PK digestion) were studied in two separate patient and control cohorts. Anti-p-α-syn stain was performed in parallel.
Single sections from at least 2 biopsy sites from 44 patients and 22 controls (cohort 1) as well as serial sections of 4 biopsy sites from 27 patients and 5 controls (cohort 2) were systematically studied for presence of aggregated and oligomeric α-syn. In total, 5G4 positive deposits were found in 24% (cohort 1) and 37% (cohort 2), ASyO5 positive lesions in 17,7% (cohort 1) and 33% (cohort 2), syn211 positive lesions after PK digestion in 38,7% (cohort 1) and 48% (cohort 2) of cases. There was a major overlap among positivity for a particular staining on the patient level and in most cases, the same nerve fiber was found to be positive for all 4 markers in neighboring sections. Among the skin biopsies which contained p-α-syn accumulation, 59% were also PK resistant, 41% were 5G4 positive and 45% were ASyO5 positive. The samples belonging to normal controls did not show any positive signal in either of the newly established stainings or in the anti-p-α-syn staining.
Using 3 distinct IHC methods, α-syn oligomers and aggregates were detectable in the majority of p-α-syn positive skin biopsies. This finding supports the hypothesis that α-syn aggregation occurs in the peripheral (i.e. dermal) nerves and can be specifically detected using skin biopsy.
The pathophysiological mechanisms of pain in small fiber neuropathy (SFN) are unclear. Based on experimental and clinical studies, sensitized nociceptors in the skin are reported to be involved in pain development. These nociceptors may be sensitized by cutaneous and systemic pain mediators e.g. pro- and anti-inflammatory cytokines. The aim of our study was, to measure the systemic and local gene expression of pro- and anti-inflammatory cytokines in white blood cells (WBC) as well as in primary fibroblasts and keratinocytes obtained from human skin of patients with SFN. Furthermore, gene expression levels of axon guidance molecules and their receptors, as potential regulators of the intraepidermal nerve fiber density (IENFD), were investigated. 55 patients and 31 healthy controls were prospectively recruited. Participants underwent extensive clinical phenotyping and blood sampling, 6-mm skin punch biopsies were taken from the right lateral calf and the upper thigh. Systemic relative gene expression levels (ΔG) of the interleukin (IL)-1β, IL-2, IL-6, IL-8, and tumor necrosis factor (TNF) was measured in WBC. Skin punch biopsies were taken to determine the IENFD and to obtain primary fibroblast and keratinocyte cell cultures. Skin cells were then used for investigation of ΔG in axon guidance molecules netrin 1 (NTN1) and ephrin A4 (EPHA4) as well as their receptors Unc5b receptor, and ephrin A4 (EFNA4) as well as cytokines IL-1β, IL-4, IL-6, IL-8, IL-10, TNF, and transforming growth factor (TGF). Systemically, gene expression of IL-2, IL-8, and TNF was higher in SFN patients compared to healthy controls. In keratinocytes, higher expression levels of NTN1 and TGF were found when comparing the SFN patients to the controls. In fibroblasts higher gene expression was shown in NTN1, Unc5b, IL-6, and IL-8 when comparing patients to healthy controls. The systemically and local elevated levels of pro-inflammatory, algesic cytokines in SFN patients compared to healthy controls, confirms a potential pathophysiological role in the development of neuropathic pain. Data also indicate fibroblasts and keratinocytes to influence subepidermal and intraepidermal nerve fiber growth through the expression of NTN1 and Unc5b. Thus, skin cells may contribute to the development of neuropathic pain through local denervation.
Development Of A Human iPSC-Derived Cortical Neuron Model Of Adaptor- Protein-Complex-4-Deficiency
(2024)
Adaptor-protein-4-deficiency (AP-4-deficiency) is an autosomal-recessive childhood- onset form of complicated hereditary spastic paraplegia (HSP) caused by bi-allelic loss- of-function mutations in one of the four subunits of the AP-4-complex. These four conditions are named SPG47 (AP4B1, OMIM #614066), SPG50 (AP4M1, OMIM #612936), SPG51 (AP4E1, OMIM #613744) and SPG52 (AP4S1, OMIM #614067), respectively and all present with global developmental delay, progressive spasticity and seizures. Imaging features include a thinning of the corpus callosum, ventriculomegaly and white matter changes. AP-4 is a highly conserved heterotetrameric complex, which is responsible for polarized sorting of transmembrane cargo including the autophagy- related protein 9 A (ATG9A). Loss of any of the four subunits leads to an instable complex and defective sorting of AP-4-cargo. ATG9A is implicated in autophagosome formation and neurite outgrowth. It is missorted in AP-4-deficient cells and CNS-specific knockout of Atg9a in mice results in a phenotype reminiscent of AP-4-deficiency. However, the AP-4-related cellular phenotypes including ATG9A missorting have not been investigated in human neurons.
Thus, the aim of this study is to provide the first human induced pluripotent stem cell- derived (iPSC) cortical neuron model of AP-4-deficiency to explore AP-4-related phenotypes in preparation for a high-content screening. Under the hypothesis that AP-4- deficiency leads to ATG9A missorting, elevated ATG9A levels, impaired autophagy and neurite outgrowth in human iPSC-derived cortical neurons, in vitro biochemical and imaging assays including automated high-content imaging and analysis were applied. First, these phenotypes were investigated in fibroblasts from three patients with compound heterozygous mutations in the AP4B1 gene and their sex-matched parental controls. The same cell lines were used to generate iPSCs and differentiate them into human excitatory cortical neurons.
This work shows that ATG9A is accumulating in the trans-Golgi-network in AP-4- deficient human fibroblasts and that ATG9A levels are increased compared to parental controls and wild type cells suggesting a compensatory mechanism. Protein levels of the AP4E1-subunit were used as a surrogate marker for the AP-4-complex and were decreased in AP-4-deficient fibroblasts with co-immunoprecipitation confirming the instability of the complex. Lentiviral re-expression of the AP4B1-subunit rescues this corroborating the fact that a stable AP-4-complex is needed for ATG9A trafficking. Surprisingly, autophagic flux was present in AP-4-deficient fibroblasts under nutrient- rich and starvation conditions. These phenotypic markers were evaluated in iPSC-derived cortical neurons and here, a robust accumulation of ATG9A in the juxtanuclear area was seen together with elevated ATG9A protein levels. Strikingly, assessment of autophagy markers under nutrient-rich conditions showed alterations in AP-4-deficient iPSC- derived cortical neurons indicating dysfunctional autophagosome formation. These findings point towards a neuron-specific impairment of autophagy and need further investigation. Adding to the range of AP-4-related phenotypes, neurite outgrowth and branching are impaired in AP-4-deficient iPSC-derived cortical neurons as early as 24h after plating and together with recent studies point towards a distinct role of ATG9A in neurodevelopment independent of autophagy.
Together, this work provides the first patient-derived neuron model of AP-4-deficiency and shows that ATG9A is sorted in an AP-4-dependent manner. It establishes ATG9A- related phenotypes and impaired neurite outgrowth as robust markers for a high-content screening. This disease model holds the promise of providing a platform to further study AP-4-deficiency and to search for novel therapeutic targets.
Effects of dopamine on BDNF / TrkB mediated signaling and plasticity on cortico-striatal synapses
(2021)
Progressive loss of voluntary movement control is the central symptom of Parkinson's disease (PD). Even today, we are not yet able to cure PD. This is mainly due to a lack of understanding the mechanisms of movement control, network activity and plasticity in motor circuits, in particular between the cerebral cortex and the striatum. Brain-derived neurotrophic factor (BDNF) has emerged as one of the most important factors for the development and survival of neurons, as well as for synaptic plasticity. It is thus an important target for the development of new therapeutic strategies against neurodegenerative diseases. Together with its receptor, the Tropomyosin receptor kinase B (TrkB), it is critically involved in development and function of the striatum. Nevertheless, little is known about the localization of BDNF within presynaptic terminals in the striatum, as well as the types of neurons that produce BDNF in the cerebral cortex. Furthermore, the influence of midbrain derived dopamine on the control of BDNF / TrkB interaction in striatal medium spiny neurons (MSNs) remains elusive so far. Dopamine, however, appears to play an important role, as its absence leads to drastic changes in striatal synaptic plasticity. This suggests that dopamine could regulate synaptic activity in the striatum via modulation of BDNF / TrkB function. To answer these questions, we have developed a sensitive and reliable protocol for the immunohistochemical detection of endogenous BDNF. We find that the majority of striatal BDNF is provided by glutamatergic, cortex derived afferents and not dopaminergic inputs from the midbrain. In fact, we found BDNF in cell bodies of neurons in layers II-III and V of the primary and secondary motor cortex as well as layer V of the somatosensory cortex. These are the brain areas that send dense projections to the dorsolateral striatum for control of voluntary movement. Furthermore, we could show that these projection neurons significantly downregulate the expression of BDNF during the juvenile development of mice between 3 and 12 weeks.
In parallel, we found a modulatory effect of dopamine on the translocation of TrkB to the cell surface in postsynaptic striatal Medium Spiny Neurons (MSNs). In MSNs of the direct pathway (dMSNs), which express dopamine receptor 1 (DRD1), we observed the formation of TrkB aggregates in the 6-hydroxydopamine (6-OHDA) model of PD. This suggests that DRD1 activity controls TrkB surface expression in these neurons. In contrast, we found that DRD2 activation has opposite effects in MSNs of the indirect pathway (iMSNs). Activation of DRD2 promotes a rapid decrease in TrkB surface expression which was reversible and depended on cAMP. In parallel, stimulation of DRD2 led to induction of phospho-TrkB (pTrkB). This effect was significantly slower than the effect on TrkB surface expression and indicates that TrkB is transactivated by DRD2. Together, our data provide evidence that dopamine triggers dual modes of plasticity on striatal MSNs by acting on TrkB surface expression in DRD1 and DRD2 expressing MSNs. This surface expression of the receptor is crucial for the binding of BDNF, which is released from corticostriatal afferents. This leads to the induction of TrkB-mediated downstream signal transduction cascades and long-term potentiation (LTP). Therefore, the dopamine-mediated translocation of TrkB could be a mediator that modulates the balance between dopaminergic and glutamatergic signaling to allow synaptic plasticity in a spatiotemporal manner. This information and the fact that TrkB is segregated to persistent aggregates in PD could help to improve our understanding of voluntary movement control and to develop new therapeutic strategies beyond those focusing on dopaminergic supply.
Deterioration of gait and alterations of physiological gait initiation contribute significantly to the burden of disease in Parkinson's disease. This paper systematically investigates disease-specific alterations during the postural phases of gait initiation and demonstrates the influence of dopaminergic networks by assessing levodopa mediated improvements in motor performance and correlation of motor behavior with loss of striatal and cortical dopaminergic neurons. Particular attention is given to known confounders such as initial stance and anthropometrics.
Neuropathies are a group of potentially treatable diseases with an often disabling and restricting course. Amyotrophic lateral sclerosis (ALS) is a lethal disease without causal treatment possibilities. The objective of this study was to examine the diagnostic utility of HRUS for the differentiation of subtypes of axonal and demyelinating neuropathies and to investigate its utility for the sonological differentiation of ALS.
The hypothetical statement that neuropathy causes enlargement of peripheral nerves compared to healthy controls proved to be right, but the adjunctive assumption that ALS does not cause enlargement of peripheral nerves proved to be wrong – in patients with ALS slight enlargement of peripheral nerves was visible as well. The statement that nerve enlargement can be detected by measurement of the cross-sectional area (CSA) and the longitudinal diameter (LD) with comparable results proved to be right, but the enlargement was slightly less present by measurement of the LD. The statement that axonal and demyelinating neuropathies show distinct patterns of nerve enlargement must be answered differentiated: The comparison between axonal and demyelinating neuropathies showed a stronger nerve enlargement in patients with demyelinating neuropathies than in patients with axonal neuropathies at proximal nerve segments of upper extremities. In the comparison of diagnose-defined subgroups of inflammatory demyelinating neuropathies a respective specific pattern of nerve enlargement was visible. However, remarkable in this context was the strong nerve enlargement found in patients with NSVN, which is classified as an axonal neuropathy. Stratification for specific findings in nerve biopsy did not lead to constructive differences in comparison between the different groups.
To sum up, HRUS showed to provide a useful contribution in the diagnostic process of neuropathies and ALS but needs to be integrated in a multimodal diagnostic approach.