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: 7.76). 01/2013; 65(1). DOI: 10.1002/art.37750
Source: PubMed


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.


Available from: Mona Dvir-Ginzberg, Mar 23, 2015
  • Source
    • "Furthermore, the expression level of SIRT1 is reduced over the course of OA, giving rise to hypertrophic phenotypes and OA-like gene expression patterns in chondrocytes (Fujita et al., 2011). Similarly, surgically-induced OA pathogenesis in mice was significantly accelerated by chondrocyte-specific deletion of the Sirt1 gene, with concomitant downregulation of anabolic proteins and upregulation of cartilage degrading enzymes (Gabay et al., 2013; Matsuzaki et al., 2014). Moreover, in Sirt1 CKO mice, p65 was found to be acetylated, which in turn causes activation of NF-κB pathway and consequently catabolic pathways, augmenting OA pathogenesis (Fig. 1) (Dvir-Ginzberg et al., 2011). "
    [Show abstract] [Hide abstract]
    ABSTRACT: Osteoarthritis (OA) is one of the most prevalent forms of joint disorder, associated with a tremendous socioeconomic burden worldwide. Various non-genetic and lifestyle-related factors such as aging and obesity have been recognized as major risk factors for OA, underscoring the potential role for epigenetic regulation in the pathogenesis of the disease. OA-associated epigenetic aberrations have been noted at the level of DNA methylation and histone modification in chondrocytes. These epigenetic regulations are implicated in driving an imbalance between the expression of catabolic and anabolic factors, leading eventually to osteoarthritic cartilage destruction. Cellular senescence and metabolic abnormalities driven by OAassociated risk factors appear to accompany epigenetic drifts in chondrocytes. Notably, molecular events associated with metabolic disorders influence epigenetic regulation in chondrocytes, supporting the notion that OA is a metabolic disease. Here, we review accumulating evidence supporting a role for epigenetics in the regulation of cartilage homeostasis and OA pathogenesis.
    Moleculer Cells 08/2015; 38(8). DOI:10.14348/molcells.2015.0200 · 2.09 Impact Factor
  • 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 · 4.54 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 more