The lymphocyte secretome from young adults enhances skeletal muscle proliferation and migration, but effects are attenuated in the secretome of older adults.

Sarah Al-Dabbagh,Jamie S Mcphee,Christopher Murgatroyd,Nasser Al-Shanti,Gillian Butler-Browne,Claire E Stewart

doi:10.14814/phy2.12518

Abstract

Older people experience skeletal muscle wasting, in part due to impaired proliferative capacity of quiescent skeletal muscle satellite cells which can be reversed by exposure to young blood. To investigate the role of immune cells in muscle regeneration, we isolated lymphocytes from whole blood of young and older healthy volunteers and cultured them with, or without, anti-CD3/CD28 activators to induce release of cytokines, interleukins, and growth factors into the media. The secreted proteins were collected to prepare a conditioned media, which was subsequently used to culture C2C12 myoblasts. The conditioned media from the activated young lymphocytes increased the rate of proliferation of myoblasts by around threefold (P < 0.005) and caused an approximate fourfold (P < 0.005) increase in migration compared with nonactivated lymphocyte control media. These responses were characterized by minimal myotube formation (2%), low fusion index (5%), low myosin heavy chain content, and substantial migration. In contrast, myoblasts treated with conditioned media from activated old lymphocytes exhibited a high degree of differentiation, and multi-nucleated myotube formation that was comparable to control conditions, thus showing no effect on proliferation or migration of myoblasts. These results indicate that secreted proteins from lymphocytes of young people enhance the muscle cell proliferation and migration, whereas secreted proteins from lymphocytes of older people may contribute to the attenuated skeletal muscle satellite cell proliferation and migration.

Highlights

Skeletal muscle satellite cells residing between the basal lamina and sarcolemma in a quiescent state are activated in response to muscle damage or trauma to proliferate, migrate, and differentiate to promote growth and regeneration of fibers (Tidball and Villalta 2010)
Morphological differences in the C2C12 myoblasts treated with CM1 of young and old adults
Analysis of differentiation parameters (Fusion Index, Aspect ratio, and Myotube Area, Fig. 1B, C and D) showed that young CM1-treated myoblasts exhibited less differentiation and increased rates of proliferation compared with the old CM1-treated myoblasts

Summary

Introduction

Skeletal muscle satellite cells residing between the basal lamina and sarcolemma in a quiescent state are activated in response to muscle damage or trauma to proliferate, migrate, and differentiate to promote growth and regeneration of fibers (Tidball and Villalta 2010). The progressive loss of skeletal muscle mass and strength characteristic of old age is associated with a failure to appropriately activate the satellite cells (Goldspink et al 1994; Corsetti et al 2008), impaired proliferative capacity to produce enough myoblasts essential for muscle regeneration (Conboy et al 2003), and slowed rates of migration (Price et al 2007).

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