The influence of chronic IL-6 exposure, in vivo, on rat Achilles tendon extracellular matrix

When compared to placebo, acetaminophen (APAP) reduces tendon stiffness and collagen cross-linking. APAP also enhances the exercise-induced increase in peritendinous levels of IL-6. Elevated levels of IL-6 are associated with tendinopathy, thus we hypothesized that chronic, elevated peritendinous IL-6 would alter tendon extracellular matrix (ECM). IL-6 (∼3000 pg ml−1) was injected (3 d wk−1 for 8-wks) into the Achilles peritendinous region of male Wistar rats (n = 16) with the opposite leg serving as a sham. Fractional synthesis rates (FSR) were determined using deuterium oxide. Collagen (hydroxyproline) and hydroxylysl pyridinoline (HP) cross-linking were analyzed by HPLC. ECM and IL-6 related genes were evaluated using qRT-PCR. Relative to sham, collagen (Col) 1a1 but not Col3a1 expression was suppressed (47%) in tendons exposed to IL-6 (p < 0.05). Lysyl oxidase (LOX) and MMP-1 expression were also reduced (37%) in IL-6 treated tendons (p < 0.05). Relative to sham the expression of MMP-2, -3, -9, and TIMP-1 were not altered by IL-6 treatment (p > 0.05). Interleukin-6 receptor subunit beta precursor (IL6st) was lower (16%) in IL-6 treated tendons when compared to sham (p < 0.05). Suppressor of cytokine signaling 3 (Socs3), signal transducer and activator of transcription 3 (STAT3), and protein inhibitor of activated STAT 1 (Pias1) were not altered by IL-6 exposure (p > 0.05). Neither collagen nor cross-linking content were altered by IL-6 (p > 0.05). Additionally, IL-6 treatment did not alter tendon FSR. Chronic treatment with physiologically relevant levels of IL-6 suppresses expression of Col1a1 and LOX while also altering expression of select MMPs but does not alter Achilles tendon collagen synthesis.