Distribution of Neuropeptides in the Synovium of Charcot Neuroarthropathy

Abstract

Category: Basic Sciences/Biologics Introduction/Purpose: The pathology of Charcot neuroarthropathy (CNA) presents inflammation, and bone and cartilage destruction. It is still unclear how the neuropathic signals lead to joint inflammation and destruction. Neuropeptides are secreted by neurons and involve in the regulation of inflammation. Synovium is richly innervated and known to play a critical role in the pathology of inflammatory arthritis. This study is designed to investigate the distribution of several neuropeptides, such as vasoactive intestinal peptide (VIP), substance P (SP) and calcitonin gene-related peptide (CGRP), in CNA synovium, in comparison with non-CNA synovium, with immunohistochemistry. Methods: Synovial samples were collected from CNA patients (n=3) and patients with osteoarthritis and intraarticular fracture (non-CNA; n=3), during foot and ankle surgery (approved by IRB). The tissue samples were fixed with 4% paraformaldehyde, embedded in O.T.C media and sectioned with a cryostat. From each patient, 6-9 sections were randomly selected for immunohistochemistry. After blocking the tissue sections with normal serum, primary antibody of SP, VIP and CGRP was separately applied and incubated at 4ºC overnight. The biotinylated secondary antibody and ABC kit (Victor Laboratories) were applied subsequently. DAB (3,3’-diaminobenzidine) was used for colorimetric detection (brown) of immunohistochemical reactions. The cell nuclei were stained with hematoxylin. The staining was viewed under a microscope and images were taken with a digital camera. Results: In the non-CNA synovium, SP was stained around neuro-vascular bundles and intensely stained on the surface of the synovium, i.e. the intimal layer. In the CNA synovium, SP staining was increased and more diffuse into the subintimal layer of the synovium (Fig 1). In non-CNA synovium, VIP was detected along the surface area of the synovium but not limited in the intimal layer. In CNA synovium, VIP was a similar staining pattern with a reduced staining intensity. The CGRP staining was primarily limited in the intimal layer in the non-CNA synovium. In CNA synovium, CGRP was stained in the intimal layer with an increased intensity. Conclusion: SP, VIP and CGRP are well-studied neuropeptides and have broad biological and pathological functions. All of them were detected in the intimal layer, where fibroblast-like synoviocytes are located. Fibroblast-like synoviocytes are fundamental elements of joint inflammation and are capable of degradation of bone and cartilage directly and indirectly. The changed patterns of SP, VIP and CGRP distributions in CNA synovium revealed by immunohistochemistry indicate a possible pathological pathway in CNA development: the unbalanced neuropathic signals direct fibroblast-like synoviocytes to an inflammatory state, which trigger the cascade of bone and cartilage destruction in CNA.