Muscle-specific deletion of SOCS3 increases the early inflammatory response but does not affect regeneration after myotoxic injury

Abstract

BackgroundMuscles of old animals are injured more easily and regenerate poorly, attributed in part to increased levels of circulating pro-inflammatory cytokines. The Janus kinase/signal transducers and activators of transcription (JAK/STAT) signaling cascade is a key mediator of inflammatory cytokine action, and signaling via this pathway is increased in muscles with aging. As a negative regulator of JAK/STAT signaling, a key mediator of myogenic proliferation and differentiation, altered expression of suppressor of cytokine signaling (SOCS3) is likely to have important consequences for muscle regeneration. To model this scenario, we investigated the effect of SOCS3 deletion within mature muscle fibers on injury and repair. We tested the hypothesis that reduced SOCS3 function would alter the inflammatory response and impair muscle regeneration after myotoxic injury.MethodsMice with a specific deletion of SOCS3 within mature skeletal muscle fibers were used to assess the effect of SOCS3 deletion on muscle injury and repair. Twelve-week-old or 24-month-old SOCS3 muscle-specific knockout (SOCS3 MKO) mice and littermate controls were either left uninjured or injured with a single injection of notexin (10 μg/ml) into the right tibialis anterior (TA) muscle. At 1, 2, 3, 5, 7, or 14 days post-injury, the right TA muscle was excised and subjected to histological, western immunoblotting, and gene expression analyses. Force production and fatigue were assessed in uninjured muscles and at 7 days post-notexin injury.ResultsIn uninjured muscles, SOCS3 deletion decreased force production during fatigue but had no effect on the gross or histological appearance of the TA muscles. After notexin injury, deletion of SOCS3 increased STAT3 phosphorylation at day 1 and increased the mRNA expression of the inflammatory cytokine TNF-α, and the inflammatory cell markers F4/80 and CD68 at day 2. Gene expression analysis of the regeneration markers Pax7, MyoD, and Myogenin indicated SOCS3 deletion had no effect on the progression of muscle repair after notexin injury. Inflammation and regeneration were also unchanged in the muscles of 24-month-old SOCS3 MKO mice compared with control.ConclusionsLoss of SOCS3 expression in mature muscle fibers increased the inflammatory response to myotoxic injury but did not impair muscle regeneration in either adult or old mice. Therefore, reduced SOCS3 expression in muscle fibers is unlikely to underlie impaired muscle regeneration. Further investigation into the role of SOCS3 in other cell types involved in muscle repair is warranted.Electronic supplementary materialThe online version of this article (doi:10.1186/s13395-016-0108-4) contains supplementary material, which is available to authorized users.

Muscle-specific deletion of SOCS3 does not reduce the anabolic response to leucine in a mouse model of acute inflammation

“…The SOCS3 muscle-specific knockout (SOCS3-MKO) mice were generated as described previously [8,15]. The muscle specific deletion of Socs3 in these mice has been confirmed in our previous studies [15]…”

“…SOCS3 is a key negative regulator of STAT3 and a critical regulator of inflammatory signaling in several tissue types, including skeletal muscle [15]. Due to its known role in the regulation of inflammation we hypothesized that SOCS3 deletion in skeletal muscle would enhance the inflammatory response to LPS injection and reduce the anabolic response to leucine.…”

“…Muscle-specific overexpression of SOCS3 impairs insulin sensitivity in overweight mice [11], yet improves muscle morphology [4,13]. In contrast, muscle-specific SOCS3 deletion improved glucose homeostasis [8], but increased the early inflammatory response after myotoxic injury [15]. Whether SOCS3 is also implicated in the regulation of anabolic signaling in skeletal muscle has yet to be established.…”

CXCL10 increases in human skeletal muscle following damage but is not necessary for muscle regeneration

“…Thus, gene expression was calculated by 2 −CT normalized to the concentration of cDNA in the PCR the reaction, as others have done (Swiderski et al. ; van Poel et al. ).…”

“…CTX injury results in complete destruction of muscle fibers thus, it is difficult to find a stable housekeeping gene in the face of a CTX injury. Thus, gene expression was calculated by 2 ÀCT normalized to the concentration of cDNA in the PCR the reaction, as others have done (Swiderski et al 2016;van Poel et al 2011).…”