Modulation of Klotho expression in injured muscle perturbs Wnt signalling and influences the rate of muscle growth

Abstract

Skeletal muscle injuries activate a complex programme of myogenesis that can restore normal muscle structure. We tested whether modulating the expression of klotho influenced the response of mouse muscles to acute injury. Our findings show that klotho expression in muscle declines at 3 days post-injury. That reduction in klotho expression coincided with elevated expression of targets of Wnt signalling (Ccnd1; Myc) and increased MyoD + muscle cell numbers, reflecting the onset of myogenic cell differentiation. klotho expression subsequently increased at 7 days post-injury with elevated expression occurring primarily in inflammatory lesions, which was accompanied by reduced expression of Wnt target genes (Ccnd1: 91%; Myc: 96%). Introduction of a klotho transgene maintained high levels of klotho expression over the course of muscle repair and attenuated the increases in Ccnd1 and Myc expression that occurred at 3 days postinjury. Correspondingly, transgene expression reduced Wnt signalling in Pax7 + cells, reflected by reductions in Pax7 + cells expressing active-catenin, and reduced the numbers of MyoD + cells at 3 days post-injury. At 21 days post-injury, muscles in klotho transgenic mice showed increased Pax7 + and decreased myogenin + cell densities and large increases in myofibre size. Likewise, treating myogenic cells in vitro with Klotho reduced Myod expression but did not affect Pax7 expression. Muscle inflammation was only slightly modulated by increased klotho expression, initially reducing the expression of M2-biased macrophage markers Cd163 and Cd206 at 3 days post-injury and later increasing the expression of pan-macrophage marker F480 and Cd68 at 21 days post-injury. Collectively, our study shows that Klotho modulates myogenesis and that increased expression accelerates muscle growth after injury.

Acute Impacts of Different Types of Exercise on Circulating α-Klotho Protein Levels

“…In our ST group, we observed a decrease in SαKl values at the end of the acute exercise session contrary to that found in the CR group. The only literature we found to be in accord with these results is an intervention comparable to a strength training bout of exercise in a mouse model, in which SαKl levels were noted to fall after exercise (Welc et al, 2020). Further studies are needed in humans to confirm that an acute session of strength exercise causes an immediate decrease in SαKl levels.…”

Genetic reduction of the extracellular matrix protein versican attenuates inflammatory cell infiltration and improves contractile function in dystrophic mdx diaphragm muscles

“…To demonstrate that versican synthesis and remodelling are associated with inflammation and regeneration in dystrophic diaphragm muscles, serial sections were used to co-localize versikine with desmin or CD68. Desmin is expressed in activated satellite cells and newly regenerated muscle fibres 55 , whilst CD68 is expressed by infiltrating monocytes and macrophages in various models of muscle damage, includes dystrophic muscles from mdx mice and patients with DMD 56,57,99,100 . Serial sections were used, because the anti-verskine, anti-CD68 (Abcam; ab125212) and anti-desmin (Abcam; ab15200) antibodies were all raised in the same species (rabbit).…”

“…To demonstrate the association between versican remodelling and regenerative myogenesis or inflammation, serial diaphragm muscle cross-sections were reacted with antibodies against versikine and desmin which is highly expressed in myoblasts and newly regenerated myotubes 55 or the monocytes and macrophage marker CD68 56,57 . Versikine was highly expressed in regions of mononuclear infiltrate ( Fig.…”

Divergent Roles of Inflammation in Skeletal Muscle Recovery From Injury

“…Agerelated perturbations in IL-33 expression may similarly disrupt regeneration by altering the accumulation of T reg cells in the satellite cell niche (Kuswanto et al, 2016). Additional changes to the satellite cell microenvironment including increased fibroblast growth factor-2 (FGF-2) expression, loss of fibronectin, systemic increases in GDF11, impaired β1-Integrin signaling, and attenuated levels of the anti-aging hormone Klotho have all been implicated in the poor repair of skeletal muscle with aging (Chakkalakal et al, 2012;Egerman et al, 2015;Lukjanenko et al, 2016;Rozo et al, 2016;Sahu et al, 2018;Welc et al, 2020).…”