Abstract
RESEARCH TYPE: Level 5 - Case report, Expert opinion, Personal observation INTRODUCTION/PURPOSE: Diabetic Charcot neuroarthropathy (DCA) is one of the diabetic complications characterized by painless progressive and destructive osteoarthropathy. The presence of peripheral neuropathy is currently considered an important prerequisite for the DCA. However, the specific pathogenic mechanism of DCA neuropathy remains unclear. Thus, we tried to quantify the nerve fibers in the DCA synovial tissue by the different immunologic stains. METHODS: Synovial tissue samples were collected from DCA and OA patients (7 for each), and NGF expression was analyzed using DNA methylation analysis and single-cell sequencing analysis. The distribution of different nerve fibers in the synovium of DCA patients and the relationship between NGF were examined by staining with HE, immunohistochemistry (NGF), and immunofluorescence (PGP9.5, CGRP, TH and VIP) RESULTS: Compared with OA, total nerve fiber density (PGP9.5+) in the DCA synovium was increased, and sensory nerve fibers (CGRP+) was significantly increased. No significant difference was found in adrenergic sympathetic fibers (TH+). Nerve growth factor (NGF) was significantly increased in the synovium of DCA. CONCLUSION: These results suggest that the increased CGRP and relatively low adrenergic sympathetic fibers may be responsible for the local dramatic inflammation and dilated blood vessels. Lesions in the sensory pathway may block the neurofeedback regulation, and resulting in excessive release of local pro-inflammatory NGF, sensory neuropeptides leading to uncontrolled local inflammatory factors releasing. Figure 1. The genome-wide methylation analysis of patients with DCA revealed that the NGF signaling pathways were among the TOP30 signaling pathways identified in the KEGG database. Synovial single cell sequencing results evealed an upregulation of NGF expression in synovial fibroblasts. Cell classification analysis further demonstrated that the increased NGF expression was observed in secretory, invasive, and protective FLS subpopulations, accompanied by a corresponding elevation in RAMP (receptor of CGRP) expression. Compared with OA, we found that the total nerve fiber density (PGP9.5+) in the DCA synovium was increased, and the number of sensory nerve fibers (CGRP+) was significantly increased.