Hyaluronan Fragment‑Driven Inflammatory Niche Suppresses Thyroarytenoid Satellite Cell Differentiation in Presbyphonia

Presbyphonia involves concurrent extracellular matrix (ECM) remodeling in the vocal fold lamina propria and atrophy of the thyroarytenoid (TA) muscle, yet aged TA muscle retains more activated satellite cells than limb muscles while failing to regenerate effectively【2】【5】. This paradox suggests that satellite cell activation is uncoupled from downstream differentiation or fusion, a step that could be blocked by changes in the local microenvironment. Recent work highlights hyaluronan (HA) as a key lamina propria glycosaminoglycan whose size and organization shift with age, producing low‑molecular‑weight fragments that act as damage‑associated molecular patterns【1】. We hypothesize that age‑related accumulation of fragmented HA in the vocal fold lamina propria creates a chronic low‑grade inflammatory niche that impairs TA satellite cell differentiation through Toll‑like receptor 4 (TLR4)–mediated NF‑κB signaling, thereby decoupling satellite cell activation from functional regeneration.

Mechanistic rationale: Low‑molecular‑weight HA binds TLR4 on resident fibroblasts and immune cells, triggering NF‑κB activation and secretion of pro‑inflammatory cytokines (IL‑1β, TNF‑α, IL‑6)【3】. These cytokines are known to inhibit myogenic differentiation by activating STAT3 and suppressing MyoD expression in satellite cells【4】. In aged TA muscle, satellite cells remain Pax7⁺ and activated (as shown by increased Myf5 expression) but fail to upregulate differentiation markers such as Myogenin and MyHC【2】. We propose that the HA‑TLR4‑NF‑κB axis creates a paracrine barrier that maintains satellite cells in a proliferative, non‑differentiating state.

Testable predictions: 1) Vocal fold lamina propria from aged humans or rodents will exhibit elevated levels of low‑molecular‑weight HA (<200 kDa) compared with young tissue, detectable by ELISA or HPLC‑SEC. 2) Immunostaining will show co‑localization of HA fragments with TLR4⁺ fibroblasts and elevated nuclear NF‑κB p65 in the lamina propria. 3) Conditioned medium from HA‑fragment‑stimulated lamina propria fibroblasts will suppress Myogenin expression and myotube formation in isolated TA satellite cells in vitro; this suppression will be rescued by TLR4 antagonist (TAK‑242) or NF‑κB inhibitor (BAY 11‑7082). 4) In vivo, local injection of high‑molecular‑weight HA (to restore HA viscosity) or TLR4 blockade into aged rat vocal folds will improve bupivacaine‑induced TA regeneration, measured by increased fiber cross‑sectional area and Pax7⁺/MyoD⁺ satellite cell differentiation, without altering satellite cell activation levels.

Falsifiable outcomes: If HA fragment levels do not increase with age, or if TLR4/NF‑κB inhibition fails to enhance satellite cell differentiation and muscle regeneration despite reducing inflammation, the hypothesis would be refuted. Conversely, confirmation would identify a novel ECM‑immune‑muscle crosstalk target for pharmacological or biomaterial interventions, addressing the mechanistic gap highlighted in the field【1】【6】.