Frozen Shoulder as a Metabolic and Immune Disorder: Potential Roles of Leptin Resistance, JAK-STAT Dysregulation, and Fibrosis

Frozen shoulder (FS) is a complex and multifactorial condition characterized by persistent inflammation, fibrosis, and metabolic dysregulation. Despite extensive research, the underlying drivers of FS remain poorly understood. Recent findings indicate the coexistence of pro-inflammatory and fibrosis-resolving macrophages within affected tissues, suggesting a dysregulated immune response influenced by metabolic and neuroendocrine factors. This review proposes that leptin resistance, a hallmark of metabolic syndrome and chronic inflammation, may play a central role in FS pathogenesis by impairing macrophage polarization, perpetuating inflammation, and disrupting fibrosis resolution. The JAK-STAT signaling pathway, critically modulated by leptin resistance, may further contribute to immune dysregulation by sustaining inflammatory macrophage activation and interfering with tissue remodeling. Additionally, FS shares pathogenic features with fibrotic diseases driven by TGF-β signaling, mitochondrial dysfunction, and circadian disruption, further linking systemic metabolic dysfunction to localized fibrotic pathology. Beyond immune and metabolic regulation, alterations in gut microbiota, bacterial translocation, and chronic psychosocial stress may further exacerbate systemic inflammation and neuroendocrine imbalances, intensifying JAK-STAT dysregulation and leptin resistance. By examining the intricate interplay between metabolism, immune function, and fibrotic remodeling, this review highlights targeting leptin sensitivity, JAK-STAT modulation, and mitochondrial restoration as novel therapeutic strategies for FS treatment. Future research should explore these interconnections to develop integrative interventions that address both the metabolic and immune dysregulation underlying FS, ultimately improving clinical outcomes.