Autophagy activation by rapamycin reduces severity of experimental osteoarthritis

Department of Molecular and Experimental Medicine, The Scripps Research Institute, La Jolla, California, USA.
Annals of the rheumatic diseases (Impact Factor: 10.38). 11/2011; 71(4):575-81. DOI: 10.1136/annrheumdis-2011-200557
Source: PubMed


Osteoarthritis is associated with cell death and extracellular matrix degradation in articular cartilage. Autophagy is an essential cellular homeostasis mechanism that was found to be deficient in ageing and osteoarthritic cartilage. This study determined whether pharmacological inhibition of the mammalian target of rapamycin (mTOR), a key inhibitor of autophagy, has disease-modifying activity in experimental osteoarthritis.
Experimental osteoarthritis was induced by transection of the medial meniscotibial ligament and the medial collateral ligament in 2-month-old C57Bl/6 mice (n=36). Rapamycin (1 mg/kg weight/day) (n=18 mice) or dimethyl sulphoxide vehicle control (n=18 mice) was administered intraperitoneally for 10 weeks. Histopathological changes in articular cartilage and synovium were examined by using semiquantitative scoring systems. Rapamycin effects on mTOR signalling, autophagy, cartilage homeostasis and inflammation were analysed by immunohistochemistry and immunofluorescence staining.
Rapamycin affected the mTOR signalling pathway in mouse knee joints as indicated by the inhibition of ribosomal protein S6 phosphorylation, a target of mTOR and activation of LC3, a main marker of autophagy. The severity of cartilage degradation was significantly (p<0.01) reduced in the rapamycin-treated group compared with the control group and this was associated with a significant (p<0.05) decrease in synovitis. Rapamycin treatment also maintained cartilage cellularity and decreased ADAMTS-5 and interleukin-1β expression in articular cartilage.
These results suggest that rapamycin, at least in part by autophagy activation, reduces the severity of experimental osteoarthritis. Pharmacological activation of autophagy may be an effective therapeutic approach for osteoarthritis.

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    • "In 2004, the term ‘chondroptosis’ was the first to define this type cell death, which includes classical apoptosis and autophagy (34). In a number of instances, the cell switches between the above two responses in a mutually exclusive manner (35). As for the non-apoptotic mechanism, numerous studies have examined the roles of autophagy in normal cartilage metabolism and pathological conditions. "
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    ABSTRACT: For the past 60 years, glucocorticosteroid (GC) drugs, including prednisone and dexamethasone (Dex), have been used for the treatment of early stage osteoarthritis (OA). However, multiple administration of GCs may destroy the articular cartilage. It has been previously reported that GC treatment may also lead to the initiation of autophagy, which is an essential mechanism for cell homeostasis and survival. Rapamycin (Rapa), an inhibitor of the mammalian target of Rapamycin, may cause a degeneration‑associated pathology in organs and induce autophagy in a variety of cell types, which has been applied in the treatment of experimental OA. A previous study by our group observed that GC apparently increases the apoptosis of chondrocytes, resulting in the inhibition of extracellular matrix synthesis. Therefore, the present study aimed to further examine the effects of autophagy in chondrocytes under GC treatment and to verify the molecular mechanisms involved in the cytoprotective role of Rapa. Short‑term GC treatment did not significantly inhibit chondrocyte viability, while cell autophagy was increased. In addition, upregulation of autophagy by Rapa prevented the expression of apoptosis‑associated genes and improved cell activity. In conclusion, the present study revealed that increased autophagy is an adaptive response to protect chondrocytes from short‑term GC exposure, whereas prolonged GC treatment decreases autophagy and increases apoptosis in vitro. Upregulation of autophagy by Rapa may protect chondrocytes against the adverse effect induced by GC.
    Full-text · Article · Apr 2014 · Molecular Medicine Reports
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    • "The regulation of autophagy also prevents diabetes, which induces damage to the endoplasmic reticulum (19). Autophagy is closely associated with human osteoarthritis and the arthritis model in mice, and may have a protective effect against osteoarthritis (20). In addition, autophagy has an extremely important role in preventing damage to the mitochondrion and the endoplasmic reticulum, and may effectively remove damaged organelles, thus delaying or preventing apoptosis initiation, reversing cell injury or degeneration, or even death (21). "
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    ABSTRACT: The aim of this study was to observe autophagy in chondrocytes from degenerative human cervical vertebral end-plates and to investigate the significance of variations in autophagy in the degeneration of cervical vertebral end-plate chondrocytes. Cartilage end-plates were obtained from 48 inpatients admitted to hospital between February 2011 and August 2012. The patients were divided into the control group (n=17) with cervical vertebral fracture or dislocation and the cervical spondylosis group (n=31) with cervical spondylotic myelopathy. End-plate chondrocytes were isolated via enzyme digestion and then cultured in vitro. The cells were stained with toluidine blue and hematoxylin-eosin (H&E). A laser scanning confocal microscope and monodansylcadaverine (MDC) were used to reveal autophagy in the end-plate chondrocytes. Reverse transcription polymerase chain reaction (RT-PCR) was used to detect mRNA expression of type II collagen and aggrecan. Western blotting was conducted to detect LC3 proteins. The chondrocytes isolated from the degenerative human cervical end-plates were cultured successfully in vitro. The morphology of the cells from the cervical spondylosis group tended to exhibit changes in spindle morphology compared with the control group. Autophagic bodies were stained with MDC. LC3 proteins were visible in the intracellular and perinuclear regions under the laser scanning confocal microscope. The mRNA expression levels (relative to those of β-actin) of aggrecan (0.715±0.194) and type II collagen (0.628±0.254) in the cervical spondylosis group were markedly decreased compared with those in the control group (0.913±0.254 and 0.845±0.186, respectively; both P<0.05). The LC3-II/LC3-I ratio was observed to be significantly reduced in the cervical spondylosis group by Western blot analysis. Autophagy has an important role in human cervical disc degeneration. The regulation of autophagy may prevent disc degeneration in cartilage end-plate cells.
    Full-text · Article · Mar 2014 · Experimental and therapeutic medicine
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    • "Alternatively, mTOR (mammalian target of rapamycin) is considered a key regulator of cell growth and proliferation [15], and its expression has been reported both in fetal chondrocytes in animal studies [16] [17] [18] and in human articular chondrocytes [19]. Moreover, treatment of mice with the mTOR inhibitor rapamycin or its analogs, has been recently shown to reduce the severity of experimental osteoarthritis [20] [21] and inflammatory arthritis [19] [22]. "
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    ABSTRACT: The gene expression of mTOR, autophagy-related ULK1, caspase 3, CDK-inhibitor p21, and TNF α was measured in the peripheral blood of osteoarthritic (OA) patients at different stages of the disease aiming to establish a gene expression profile that might indicate the activity of the disease and joint destruction. Whole blood of 65 OA outpatients, 27 end-stage OA patients, 27 healthy volunteers, and knee articular cartilages of 28 end-stage OA patients and 26 healthy subjects were examined. OA outpatients were subjected to clinical testing, ultrasonography, and radiographic and WOMAC scoring. Protein levels of p70-S6K, p21, and caspase 3 were quantified by ELISA. Gene expression was measured using real-time RT-PCR. Upregulation of mTOR gene expression was observed in PBMCs of 42 OA outpatients ("High mTOR expression subset") and in PBMCs and articular cartilages of all end-stage OA patients. A positive correlation between mTOR gene expression in PBMCs and cartilage was observed in the end-stage OA patients. 23 OA outpatients in the "Low mTOR expression subset" exhibited significantly lower mTOR gene expression in PBMCs compared to healthy controls. These "Low mTOR" subset subjects experienced significantly more pain upon walking, and standing and increased total joint stiffness versus "High mTOR" subset, while the latter more often exhibited synovitis. The protein concentrations of p70-S6K, p21, and caspase 3 in PBMCs were significantly lower in the "Low" subset versus "High" subset and end-stage subjects. Increases in the expression of mTOR in PBMCs of OA patients are related to disease activity, being associated with synovitis more than with pain.
    Full-text · Article · Jun 2013
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