Heightened muscle inflammation susceptibility may impair regenerative capacity in aging humans

Abstract

The regenerative response of skeletal muscle to mechanically induced damage is impaired with age. Previous work in our laboratory suggests this may result from higher proinflammatory signaling in aging muscle at rest and/or a greater inflammatory response to damage. We, therefore, assessed skeletal muscle proinflammatory signaling at rest and 24 h after unaccustomed, loaded knee extension contractions that induced modest muscle damage (72% increase in serum creatine kinase) in a cohort of 87 adults across three age groups (AGE40, AGE61, and AGE76). Vastus lateralis muscle gene expression and protein cell signaling of the IL-6 and TNF-α pathways were determined by quantitative PCR and immunoblot analysis. For in vitro studies, cell signaling and fusion capacities were compared among primary myoblasts from young (AGE28) and old (AGE64) donors treated with TNF-α. Muscle expression was higher (1.5- to 2.1-fold) in AGE76 and AGE61 relative to AGE40 for several genes involved in IL-6, TNF-α, and TNF-like weak inducer of apoptosis signaling. Indexes of activation for the proinflammatory transcription factors signal transducer and activator of transcription-3 and NF-κB were highest in AGE76. Resistance loading reduced gene expression of IL-6 receptor, muscle RING finger 1, and atrogin-1, and increased TNF-like weak inducer of apoptosis receptor expression. Donor myoblasts from AGE64 showed impaired differentiation and fusion in standard media and greater NF-κB activation in response to TNF-α treatment (compared with AGE28). We show for the first time that human aging is associated with muscle inflammation susceptibility (i.e., higher basal state of proinflammatory signaling) that is present in both tissue and isolated myogenic cells and likely contributes to the impaired regenerative capacity of skeletal muscle in the older population.

OPN‐a induces muscle inflammation by increasing recruitment and activation of pro‐inflammatory macrophages

“…This stimulus was previously observed to induce mild muscle damage and inflammation (Merritt et al . 2013). Here, we observed, similar to DMD patient muscle biopsies, that OPN‐a , not OPN‐c , was the most prominent isoform upregulated in response to mechanical loading.…”

Ribosome biogenesis may augment resistance training-induced myofiber hypertrophy and is required for myotube growth in vitro

“…Skeletal muscle satellite cells were isolated from an untrained young adult male (28 yr) according to previously established procedures (30). Briefly, Ϸ50 mg of muscle tissue were minced, subjected to pronase digestion, preplated to remove fibroblasts, and maintained on collagen-coated tissue culture plates at 37°C humid atmosphere with 5% CO 2.…”

Muscle inflammation susceptibility: a prognostic index of recovery potential after hip arthroplasty?

“…As we have described in more detail elsewhere (19,21), muscle samples (ϳ30 mg) were homogenized after a 15-min preincubation in 6 l/mg muscle of ice-cold lysis buffer with protease and phosphatase inhibitors and then centrifuged at 15,000 g for 40 min at 4°C. The supernatant was stored at Ϫ80°C until assayed for protein content using the bicinchoninic acid technique with BSA as a standard.…”

“…Muscle transcript levels for 10 genes involved in proinflammatory, proteolytic, and anabolic processes were quantified via quantitative (q)RT-PCR using Taqman gene expression assays (Applied Biosystems, Foster City, CA) as we have described previously (21,33). Briefly, cDNA was synthesized via reverse transcription using the SuperScript VILO cDNA synthesis kit (Invitrogen, Carlsbad, CA).…”

“…Immunoblotting was performed as we have detailed elsewhere (2,20,21) Thr32 (no. 9464) were purchased from Cell Signaling Technologies (Danvers, MA) and used at 1:1,000 dilution in either 5% goat serum (monoclonal antibodies) or 2% milk/2% BSA (polyclonal antibodies).…”