Neuroimmune Crosstalk Between Macrophages and Tendon-Derived Cells Across Distinct Tendon Regions

Abstract

Chronic tendon pain is a major contributor to musculoskeletal disability, yet the biological mechanisms driving tendinopathic pain remain poorly understood. Emerging evidence implicates neuroimmune signaling in tendon inflammation and pain, including Substance P (SP) and tumor necrosis factor-α (TNF-α). Although elevated expression of these mediators are associated with nociceptive signaling, interactions between the primary parenchymal cells in the tissue and neuroimmune pathways remain unclear. Understanding this crosstalk is essential for linking inflammation to pain at the cellular level. Preliminary data demonstrate an increase in endogenous SP and TNF-α secretion from rat Achilles tendon-derived cells (TDCs) exposed to inflammatory stimuli, suggesting a role for SP in tendon inflammation. However, it remains unclear whether this response is conserved across tendons. This study compares supraspinatus and Achilles TDCs to access whether immunomodulatory responses are conserved across anatomically and mechanically distinct tendon environments. TDCs from both tendon types will be treated with unpolarized (MO, baseline) and polarized (M1, pro-inflammatory) macrophage-conditioned media, and SP and TNF-α secretion will be quantified. We hypothesize that exposure to inflammatory stimuli will increase SP and TNF-α secretion in TDCs, with tendon-specific differences reflecting the distinct microenvironments. These findings will advance our understanding of neuroimmune mechanisms underlying tendon pain.