Suppression of Sestrins in aging and osteoarthritic cartilage: dysfunction of an important stress defense mechanism.
Aging is an important osteoarthritis (OA) risk factor and compromised stress defense responses may mediate this risk. The Sestrins (Sesn) promote cell survival under stress conditions and regulate AMP-activated protein kinase (AMPK) and mammalian target of rapamycin (mTOR) signaling. This study examined Sesn expression in normal and OA cartilage and functions of Sesn in chondrocytes.



Sesn expression in human and mouse normal and OA cartilage was analyzed by quantitative polymerase chain reaction (PCR) and immunohistochemistry. Sesn function was investigated by using small interfering RNA (siRNA) mediated Sesn knockdown and overexpression with analysis of cell survival, gene expression, autophagy, and AMPK and mTOR activation.



Sesn mRNA levels were significantly reduced in human OA cartilage and immunohistochemistry of human and mouse OA cartilage also showed a corresponding reduction in protein levels. In cultured human chondrocytes Sesn1, 2 and 3 were expressed and increased by tunicamycin, an endoplasmic reticulum (ER) stress response inducer and 2-deoxyglucose (2DG), a metabolic stress inducer. Sesn1 and 2 were increased by tBHP, an oxidative stress inducer. Sesn knockdown by siRNA reduced chondrocyte viability under basal culture conditions and in the presence of 2DG. Sesn overexpression enhanced LC3-II formation and autophagic flux, and this was related to changes in mTOR but not AMPK activation.



These findings are the first to show that Sesn expression is suppressed in OA affected cartilage. Sesn support chondrocyte survival under stress conditions and promote autophagy activation through modulating mTOR activity. Suppression of Sesn in OA cartilage contributes to deficiency in an important cellular homeostasis mechanism.
Department of Molecular and Experimental Medicine, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, CA, USA; Department of Orthopedic Surgery, Shengjing Hospital, China Medical University, No. 36, Sanhao Street, Shenyang 110004, People's Republic of China. Electronic address: shent@sj-hospital.org.
T
T
Shen
Department of Molecular and Experimental Medicine, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, CA, USA. Electronic address: ogarcia@scripps.edu.
O
O
Alvarez-Garcia
Department of Orthopedic Surgery, Shengjing Hospital, China Medical University, No. 36, Sanhao Street, Shenyang 110004, People's Republic of China. Electronic address: cmuyanli@hotmail.com.
Y
Y
Li
Department of Molecular and Experimental Medicine, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, CA, USA. Electronic address: molmer@scripps.edu.
M
M
Olmer
Department of Molecular and Experimental Medicine, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, CA, USA. Electronic address: mlotz@scripps.edu.
M K
MK
Lotz
D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000375:Aging / Q000378:metabolism; D000818:Animals; D002358:Cartilage, Articular / Q000378:metabolism*; D019902:Chondrocytes / Q000187:drug effects / Q000378:metabolism; D003847:Deoxyglucose / Q000494:pharmacology; D005260:Female; D055785:Gene Knockdown Techniques / Q000379:methods; D006360:Heat-Shock Proteins / Q000378:metabolism*; D006801:Humans; D008297:Male; D051379:Mice; D008875:Middle Aged; D009687:Nuclear Proteins / Q000378:metabolism*; D010003:Osteoarthritis / Q000378:metabolism*; D018384:Oxidative Stress / Q000187:drug effects; D034741:RNA, Small Interfering / Q000378:metabolism; D014415:Tunicamycin / Q000494:pharmacology; D055815:Young Adult; D000084622:Sestrins
D003847:Deoxyglucose; D006360:Heat-Shock Proteins; D009687:Nuclear Proteins; D034741:RNA, Small Interfering; D014415:Tunicamycin; C117338:SESN1 protein, human; D000084622:Sestrins; C465398:SESN2 protein, human; C485523:SESN3 protein, human
Autophagy; Osteoarthritis; Sestrins; mTOR
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