Mechanistic Insights Into <scp>OSM</scp> and <scp>IL</scp> ‐31 in Primary Localized Cutaneous Amyloidosis: A Narrative Review

Primary localized cutaneous amyloidosis (PLCA) is a chronic pruritic dermatological disorder characterized by amyloid deposits in the papillary dermis, significantly impairing patients' quality of life. Although the pathogenesis of PLCA is multifaceted, emerging evidence highlights the pivotal role of dysregulated cytokines, particularly the members of interleukin-6 (IL-6) cytokines family in PLCA. Oncostatin M (OSM) mediates keratinocyte proliferation through the STAT5-KLF7 axis upon OSMRβ engagement. Pathogenic variants in OSMR disrupt receptor dimerization, thereby suppressing signal transduction. These alterations together with cytokine dysregulation concomitantly elevate the expression of AHNAK and suppress that of Bcl-xL, which accelerate keratinocyte differentiation and apoptosis respectively, leading to the thickening of the stratum corneum and amyloid fibril deposition. Furthermore, dysregulated expression of chemokine monocyte chemoattractant protein-1 (MCP-1) by pathogenic variant in IL-31RA reduces monocyte-mediated clearance of amyloid fibrils, thereby promoting their pathological retention. The mechanisms of IL-31-mediated pruritus remain to be elucidated, given the conflicting observations that while some studies report wider cutaneous innervation in FPLCA patients, others demonstrate opposing results in general lichen amyloidosis patients. This review aims to synthesize recent advances in understanding PLCA pathogenesis with a focus on IL-31 and OSM cytokines network dysregulation especially driven by pathogenic variants, and provide critical insights for identifying therapeutic targets and put forward challenges in the future.