Hyperphosphatemia Promotes Senescence of Myoblasts by Impairing Autophagy Through Ilk Overexpression, A Possible Mechanism Involved in Sarcopenia

Abstract

In mammalians, advancing age is associated with sarcopenia, the progressive and involuntary loss of muscle mass and strength. Hyperphosphatemia is an aging-related condition involved in several pathologies. The aim of this work was to assess whether hyperphosphatemia plays a role in the age-related loss of mass muscle and strength by inducing cellular senescence in murine myoblasts and to explore the intracellular mechanism involved in this effect. Cultured mouse C2C12 cells were treated with 10 mM beta-glycerophosphate (BGP] at different periods of time to induce hyperphosphatemia. BGP promoted cellular senescence after 24 h of treatment, assessed by the increased expression of p53, acetylated-p53 and p21 and senescence associated β-galactosidase activity. In parallel, BGP increased ILK expression and activity, followed by mTOR activation and autophagy reduction. Knocking-down ILK expression increased autophagy and protected cells from senescence induced by hyperphosphatemia. BGP also reduced the proliferative capacity of cultured myoblasts. Old mice (24-months-old] presented higher serum phosphate concentration, lower forelimb strength, higher expression of p53 and ILK and less autophagy in vastus muscle than young mice (5-months-old]. In conclusion, we propose that hyperphosphatemia induces senescence in cultured myoblasts through ILK overexpression, reducing their proliferative capacity, which could be a mechanism involved in the development of sarcopenia, since old mice showed loss of muscular strength correlated with high serum phosphate concentration and increased levels of ILK and p53.

Endothelin-1 induces cellular senescence and fibrosis in cultured myoblasts. A potential mechanism of aging-related sarcopenia

“…Raz et al suggested that chronic age-associated muscle degeneration was associated with higher fibrosis in muscle [31] and the relationship between muscular AGING fibrosis and loss of strength has also been described in several muscular dystrophies [57]. With respect to senescence increased in old mice, previous results from our group [19,45] are in agreement, as they found that old mice had high levels of serum phosphate linked to increased expression of ILK and senescence genes.…”

“…Cellular senescence can be induced prematurely by activated oncogenes, DNA damage and oxidative stress [15,16] as well as by extracellular systemic factors such as hyperosmolarity, high glucose [17] and glycated albumin [18]. In this sense, we have recently described that elevated extracellular phosphate concentration induced senescence in cultured myoblasts, disrupting the autophagy mechanism through ILK overexpression [19].…”

“…We have previously described that cultured myoblast undergo cellular senescence after exposition to high extracellular phosphate concentration, compromising the regenerative capacity of the muscle [19]. In addition, hyperphosphatemia, which dramatically affects the behavior of vascular cells [34], increases ECE-1 activity in endothelial cells, which induces the synthesis of ET-1 and also senescence in endothelial cells [28].…”

The mechanisms and treatments for sarcopenia: could exosomes be a perspective research strategy in the future?

“…According to another study, impaired transport of amino acids, in particular branched‐chain amino acids, into muscle had a negative effect on protein recycling and energy utilization, which was associated with alterations in phospholipid metabolism . It is also reported that hyperphosphataemia induces senescence of cultured myoblasts by impairing autophagy and activating mTOR through integrin‐linked kinase overexpression, which could be another potential mechanism of sarcopenia …”

High phosphate levels promote muscle atrophy via myostatin expression in differentiated L6 myotubes

“…Recently, a human study by Chen et al [15] demonstrated an inverse association between serum phosphate levels and muscle strength. To the best of our knowledge, there is only one in vitro study that investigated the effect of high-phosphate conditions in mouse C 2 C 12 cells [16]. However, they examined how high phosphate levels affected the differentiation of myoblasts to myotubes, indicating that satellite cells differentiate into myotubes during the process of muscle regeneration.…”