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Age-Related Increase of Insoluble, Phosphorylated Small Heat Shock Proteins in Human Skeletal Muscle

¹ Department of Life Sciences, The Graduate School of Arts and Sciences, The University of Tokyo, Japan.
² Department of Orthopedic Surgery, Tokyo Kosei Nenkin Hospital, Japan.
³ Department of Health and Sports, Niigata University of Health and Welfare, Japan.
⁴ Department of Orthopedic Surgery, Tokyo Metropolitan Matsuzawa Hospital, Japan.

Address correspondence to Yoriko Atomi, PhD, Department of Life Sciences, University of Tokyo, 3-8-1 Meguroku, Tokyo, 153-8902, Japan. E-mail: atomi{at}idaten.c.u-tokyo.ac.jp

Among mammalian heat shock proteins (Hsps), small Hsps (sHsps) are constitutively expressed in skeletal muscles. We investigated age-related changes of phosphorylation and cellular distribution of representative sHsps (Hsp27 and B-crystallin) in human vastus lateralis muscle under resting conditions. We also examined upstream kinases which may be responsible for phosphorylation of sHsps, namely p38 mitogen-activated protein kinase (MAPK), MAPK-activated protein kinase-2, and extracellular signal-regulated kinase-1/2. The study groups consisted of nine young (15–38 years old) and nine aged (51–79 years old) patients who underwent orthopedic surgery. sHsps protein levels were higher in the insoluble fraction of aged muscles. The phosphorylated states of sHsps were enhanced in both the soluble and insoluble fraction of aged patients. The phosphorylated form of each upstream kinase was elevated in aged patients. Ubiquitinated proteins accumulated in the insoluble fractions of aged muscles. Aging mechanisms may affect the activation process of MAPKs, and the phosphorylation and accumulation of sHsps.