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The role of miR-21 in the pathophysiology of neuropathic pain using the model of B7-H1 knockout mice
(2017)
The impact of microRNA (miRNA) as key players in the regulation of immune and neuronal gene expression and their role as master switches in the pathophysiology of neuropathic pain is increasingly recognized. miR-21 is a promising candidate that could be linked to the immune and the nociceptive system. To further investigate the pathophysiological role of miR-21 in neuropathic pain, we assesed mice deficient of B7 homolog 1 (B7-H1 ko), a protein with suppressive effect on inflammatory responses.
B7-H1 ko mice and wildtype littermates (WT) of three different age-groups, young (8 weeks), middle-aged (6 months), and old (12 months) received a spared nerve injury (SNI). Thermal withdrawal latencies and mechanical withdrawal thresholds were determined. Further, we investigated anxiety-, depression-like and cognitive behavior. Quantitative real time PCR was used to determine miR-21 relative expression in peripheral nerves, dorsal root ganglia and white blood cells (WBC) at distinct time points after SNI.
Naïve B7-H1 ko mice showed mechanical hyposensitivity with increasing age. Young and middle-aged B7-H1 ko mice displayed lower mechanical withdrawal thresholds compared to WT mice. From day three after SNI both genotypes developed mechanical and heat hypersensitivity, without intergroup differences. As supported by the results of three behavioral tests, no relevant differences were found for anxiety-like behavior after SNI in B7-H1 ko and WT mice. Also, there was no indication of depression-like behavior after SNI or any effect of SNI on cognition in both genotypes. The injured nerves of B7-H1 ko and WT mice showed higher miR-21 expression and invasion of macrophages and T cells 7 days after SNI without intergroup differences. Perineurial miR-21 inhibitor injection reversed SNI-induced mechanical and heat hypersensitivity in old B7-H1 ko and WT mice.
This study reveals that reduced mechanical thresholds and heat withdrawal latencies are associated with miR-21 induction in the tibial and common peroneal nerve after SNI, which can be reversed by perineurial injection of a miR-21 inhibitor. Contrary to expectations, miR-21 expression levels were not higher in B7-H1 ko compared to WT mice. Thus, the B7-H1 ko mouse may be of minor importance for the study of miR-21 related pain. However, these results spot the contribution of miR-21 in the pathophysiology of neuropathic pain and emphasize the crucial role of miRNA in the regulation of neuronal and immune circuits that contribute to neuropathic pain.
Aim of Investigation: The neurological manifestations of Fabry’s disease, a rare, X-linked, multisystem disorder caused by alpha-galactosidase A deficiency and globotriosylceramide (Gb3) accumulation, include both peripheral and central nervous system symptoms. Here we evaluated a prospectively recruited cohort of patients with Fabry’s disease for pain, small nerve fiber function, and skin innervation. Methods: 66 patients (31 male and 35 female) were enrolled,31 patients were on ERT. All patients underwent quantitative sensory testing (QST), electrophysiological examination, and extra- and transcranial Doppler sonography. For pain and mood assessment standardized questionnaires were used. Skin biopsies were performed at the left distal leg in 38 patients for intraepidermal nerve fiber density (IENFD) assessment. Results: Age at examination did not differ significantly between women (40.2+/-16.2 years) and men (38.9+/-13.8; n.s.). 29/31 male and 19/35 female patients complained of acroparesthesias or neuropathic pain. QST abnormalities indicative of small fiber impairment were found in 26/31 male and 28/35 female patients. Electrophysiological examination of large fibers and autonomic fibers revealed pathological findings in 11/31 male and 3/35 female patients. All patients had normal Doppler sonography results. Indicators for depression were present in 14/31 male and 10/35 female patients. 20/31 male and 18/35 female patients had a skin biopsy, the IENFD was significantly reduced in male (2.0+/-2.8 fibers/mm) compared with female patients (6.7 +/- 4.4 fibers/mm). In 10 patients free from neurological symptoms, QST and IENFD abnormalities were still detected. Follow up examination after one year in 12 patients under ERT (2.1+/-1.7 years) showed improvement in some symptoms and in QST and neurophysiology in six patients with normal renal function. 20/35 female patients older than 40 y had concomitant diseases, while none of the 18 younger female patients did. The corresponding radio in male patients was 5/19 (>=40y) and 2/13 (<40y) respectively. Conclusions: Neuropathic pain and sensory deficits of the distal extremities are common in patients with Fabry’s disease. QST and IENFD analysis are important for early diagnosis of nerve involvement in Fabry’s disease. Small fiber function may improve under ERT in patients without severe renal impairment.