Sirt1 enzymatic activity is required for cartilage homeostasis in vivo.

Cartilage Biology and Orthopedic Branch National Institute of Arthritis and Musculoskeletal and Skin Diseases, NIH50 South Drive, Bethesda Maryland 20892. .
Arthritis & Rheumatology (Impact Factor: 7.87). 01/2013; 65(1). DOI: 10.1002/art.37750
Source: PubMed

ABSTRACT We and others previously demonstrated that sirtuin 1 (SIRT-1) regulates apoptosis and cartilage-specific gene expression in human chondrocytes and mouse models. This study was undertaken to determine if SIRT-1 enzymatic activity plays a protective role in cartilage homeostasis in vivo, by investigating mice with SIRT-1 mutations to characterize their cartilage.
Articular cartilage was harvested from the paws and knees of 5- and 6-month-old wild-type (WT) mice and mice homozygous for SIRT-1tm2.1Mcby (SIRT-1y/y), an allele carrying a point mutation that encodes a SIRT-1 protein with no enzymatic activity (y/y mice). Mice ages 2 days old and 6–7 days old were also examined. Mouse joint cartilage was processed for histologic examination or biochemical analyses of chondrocyte cultures.
We found that articular cartilage tissue sections from y/y mice of up to 6 months of age contained reduced levels of type II collagen, aggrecan, and glycosaminoglycan compared to sections from WT mice. In contrast, protein levels of matrix metalloproteinase 8 (MMP-8), MMP-9, and MMP-13 were elevated in the cartilage of y/y mice. In addition, chondrocyte apoptosis was elevated in SIRT-1 mutant mice as compared to their WT littermates. Consistent with these observations, protein tyrosine phosphatase 1b was elevated in the y/y mice.
Our in vivo findings in this animal model demonstrate that mice with defective SIRT-1 also have defective cartilage, with elevated rates of cartilage degradation with age. Hence, normal cartilage homeostasis requires enzymatically active SIRT-1 protein.

Download full-text


Available from: Mona Dvir-Ginzberg, Mar 23, 2015
  • Source
    • "It has been demonstrated that Sirt1 regulates apoptosis- and cartilage-specific gene expression in human chondrocytes and mouse models [20]. Mice without Sirt1 activity are characterized by reduced levels of type II collagen, aggrecan, glycosaminoglycan, and elevated levels of matrix metalloproteinases 8, 9 and 13 in the cartilage, and elevated chondrocyte apoptosis. "
    [Show abstract] [Hide abstract]
    ABSTRACT: Sirtuin 1 (Sirt1) is a nuclear enzyme from the class III histone deacetylases that modulates gene expression and is involved in bone and cartilage remodeling. The goal of our study was to evaluate Sirt1 activity in peripheral blood mononuclear cells in patients with osteoarthritis in comparison with control patients, and to determine the relationship between Sirt1 activity and production of TNFalpha, IL-6 and IL-8 by peripheral blood mononuclear cells after ex vivo treatment with resveratrol, a Sirt1 activator. A prospective study was performed to compare the activity of Sirt1 in patients with primary osteoarthritis of the knee (American College of Rheumatology criteria) with its activity in controls. Peripheral blood mononuclear cells were isolated from peripheral blood, and Sirt1 activity evaluated from cytoplasmic and nuclear compartments using a fluorometric assay. Culture supernatant levels of TNFalpha, IL-6, and IL-8 were quantified before and after resveratrol ex vivo treatment. Nineteen patients with symptomatic knee osteoarthritis (age 64 +/-9 years) and 18 controls (age 54 +/-13 years) were included. No differences were found in cytoplasmic or nuclear Sirt1 activity between patients and controls. After resveratrol treatment, no changes in TNFalpha or IL-8 levels were found, but a significant dose-dependent increase in IL-6 levels was demonstrated in patients with osteoarthritis, but not controls. Sirt1 activity did not correlate with clinical activity (Lequesne's index) or inflammation (erythrocyte sedimentation rate, C-reactive protein). Sirt1 activity (cytoplasmic and nuclear) from peripheral blood mononuclear cells did not differ between patients with osteoarthritis and controls. Ex vivo treatment of peripheral blood mononuclear cells with resveratrol was associated with a dose-dependent increase in IL-6 levels only in patients with osteoarthritis.
    Clinical Epigenetics 07/2013; 5(1):10. DOI:10.1186/1868-7083-5-10 · 6.22 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: SIRT1 is a NAD(+)-dependent protein deacetylase that has a very large number of established protein substrates and an equally impressive list of biological functions thought to be regulated by its activity. Perhaps as notable is the remarkable number of points of conflict concerning the role of SIRT1 in biological processes. For example, evidence exists suggesting that SIRT1 is a tumor suppressor, is an oncogene, or has no effect on oncogenesis. Similarly, SIRT1 is variably reported to induce, inhibit, or have no effect on autophagy. We believe that the resolution of many conflicting results is possible by considering recent reports indicating that SIRT1 is an important hub interacting with a complex network of proteins that collectively regulate a wide variety of biological processes including cancer and autophagy. A number of the interacting proteins are themselves hubs that, like SIRT1, utilize intrinsically disordered regions for their promiscuous interactions. Many studies investigating SIRT1 function have been carried out on cell lines carrying undetermined numbers of alterations to the proteins comprising the SIRT1 network or on inbred mouse strains carrying fixed mutations affecting some of these proteins. Thus, the effects of modulating SIRT1 amount and/or activity are importantly determined by the genetic background of the cell (or the inbred strain of mice), and the effects attributed to SIRT1 are synthetic with the background of mutations and epigenetic differences between cells and organisms. Work on mice carrying alterations to the Sirt1 gene suggests that the network in which SIRT1 functions plays an important role in mediating physiological adaptation to various sources of chronic stress such as calorie restriction and calorie overload. Whether the catalytic activity of SIRT1 and the nuclear concentration of the co-factor, NAD(+), are responsible for modulating this activity remains to be determined. However, the effect of modulating SIRT1 activity must be interpreted in the context of the cell or tissue under investigation. Indeed, for SIRT1, we argue that context is everything.
    Genes & cancer 03/2013; 4(3-4):125-34. DOI:10.1177/1947601912474893
  • [Show abstract] [Hide abstract]
    ABSTRACT: OBJECTIVES: Important roles for SIRT1 are implicated in ageing and age-related diseases. The role of SIRT1 in osteoarthritis (OA), however, remains partially unknown. To investigate the role of SIRT1 in chondrocytes in vivo, cartilage-specific Sirt1-conditional knockout (CKO) mice were analysed using an experimental OA model. METHODS: OA was surgically induced in 8-week-old C57BL6/J (wild-type) mice and Sirt1-CKO (Sirt1(flox)/(flox); Col2a1-Cre) mice generated using the Cre-loxP system. We examined changes in Sirt1 protein during the development of surgically-induced OA and during ageing in wild-type mice. OA progression in Sirt1-CKO mice was evaluated histologically at 2, 4 and 8 weeks after surgery, and at 1 year of age without surgery compared with control (Sirt1(flox)/(flox)) mice. RESULTS: The number of Sirt1-positive chondrocytes decreased during ageing, and although it was increased at 2 weeks after surgery, then gradually decreased to the presurgical level during the progression of OA in wild-type mice. Sirt1-CKO mice showed no obvious skeletal abnormalities. The histological OA score was significantly higher in 1-year-old Sirt1-CKO mice than in control mice. Sirt1-CKO mice showed accelerated OA progression at 2 and 4 (but not 8) weeks compared with control mice. Immunohistochemical analysis revealed increases in type X collagen, matrix metalloproteinase 13, a disintegrin and metalloproteinase with thrombospondin motifs-5, apoptotic markers, and acetylated nuclear factor-κB p65 in Sirt1-CKO mice compared with control mice 2 weeks after surgery. CONCLUSIONS: Loss of Sirt1 in chondrocytes led to the accelerated development of OA in mice. Our observations suggest that SIRT1 has a preventive role against the development of OA.
    Annals of the rheumatic diseases 05/2013; 73(7). DOI:10.1136/annrheumdis-2012-202620 · 10.38 Impact Factor
Show more