75-kd sirtuin 1 blocks tumor necrosis factor α-mediated apoptosis in human osteoarthritic chondrocytes

SIRT1 expression is associated with the chemotherapy response and prognosis of patients with advanced NSCLC

Aim

The role of Sirtuin 1 (SIRT 1) in carcinogenesis is controversial. This study was to explore the association between the SIRT1 expression and the clinical characteristics, the responsiveness to chemotherapy and prognosis in Non-small cell lung cancer (NSCLC).

Methods

We enrolled 295 patients with inoperable advanced stage of NSCLC, namely, stage III (A+B) and IV NSCLC. All patients had received platinum-based chemotherapy after diagnosis and the chemotherapy response were evaluated. All patients were followed up for overall survival (OS) and progression free survival (PFS). Invitro, H292 cells were tranfected with SIRT1 small interfering RNA (siRNA). The cell biological behaviors and chemosensitivity to cisplatin treatment were studied. The invivo tumorgenesis and metastasis assays were performed in nude mice.

Results

We found that the SIRT1 expressions were significantly associated with the tumor stage, tumor size and differentiation status. Patients with high SIRT 1 expressions had a significantly higher chance to be resistant to chemotherapy than those with low SIRT 1 expression. Patients with high expression of SIRT1 had significantly shorter OS and DFS than those with low expression. Cox analyses confirmed that the SIRT 1 expression was a strong predictor for a poor OS and PFS in NSCLC patients underwent Platinum-based chemotherapy. Invitro studies revealed that the reduced expression SIRT 1 by siRNA technique significantly inhibited cell proliferation, migration and invasion. More importantly, SIRT1 si-RNA significantly enhanced the chemosensitivity of H292 cells to cisplatin treatment. The invivo tumorgenesis and metastasis assays showed that SIRT1 knockdown dramatically reduced the tumor volume and the metastatic ability in nude mice.

Conclusion

Collectively, our data suggest that the SIRT1 expression may be a molecular marker associated with the NSLCLC clinical features, treatment responsiveness and prognosis of advanced NSCLC.

Constitutive nuclear localization of an alternatively spliced sirtuin-2 isoform

Sirtuin-2 (SIRT2), the cytoplasmic member of the sirtuin family, has been implicated in the deacetylation of nuclear proteins. Although the enzyme has been reported to be located to the nucleus during G2/M phase, its spectrum of targets suggests functions in the nucleus throughout the cell cycle. While a nucleocytoplasmic shuttling mechanism has been proposed for SIRT2, recent studies have indicated the presence of a constitutively nuclear isoform. Here we report the identification of a novel splice variant (isoform 5) of SIRT2 that lacks a nuclear export signal and encodes a predominantly nuclear isoform. This novel isoform 5 fails to show deacetylase activity using several assays, both in vitro and in vivo, and we are led to conclude that this isoform is catalytically inactive. Nevertheless, it retains the ability to interact with p300, a known interaction partner. Moreover, changes in intrinsic tryptophan fluorescence upon denaturation indicate that the protein is properly folded. These data, together with computational analyses, confirm the structural integrity of the catalytic domain. Our results suggest an activity-independent nuclear function of the novel isoform.

WISP1 neuroprotection requires FoxO3a post-translational modulation with autoregulatory control of SIRT1

As a member of the secreted extracellular matrix associated proteins of the CCN family, Wnt1 inducible signaling pathway protein 1 (WISP1/CCN4) is garnering increased attention not only as a potent proliferative entity, but also as a robust cytoprotective agent during toxic insults. Here we demonstrate that WISP1 prevents forkhead transcription factor FoxO3a mediated caspase 1 and caspase 3 apoptotic cell death in primary neurons during oxidant stress. Phosphoinositide 3-kinase (PI 3-K) and protein kinase B (Akt1) are necessary for WISP1 to foster posttranslational phosphorylation of FoxO3a and sequester FoxO3a in the cytoplasm of neurons with protein 14-3-3. Through an autoregulatory loop, WISP1 also minimizes deacytelation of FoxO3a, prevents caspase 1 and 3 activation, and promotes an effective neuroprotective level of SIRT1 activity through SIRT1 nuclear trafficking and prevention of SIRT1 caspase degradation. Elucidation of the critical pathways of WISP1 that determine neuronal cell survival during oxidative stress may offer novel therapeutic avenues for neurodegenerative disorders.

The class III histone deacetylase sirtuin 1 in immune suppression and its therapeutic potential in rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronic debilitating disease of the joints. Both the innate and adaptive immune responses participate in the development and progression of RA. While several therapeutic reagents, such as TNF-α agonists, have been successfully developed for the clinical use in the treatment of RA, more than half of the patients do not respond to anti-TNF therapy. Therefore, new therapeutic reagents are needed. Recent studies have shown that sirtuin 1 (Sirt1), a nicotinamide adenine dinucleotide (NAD)-dependent histone deacetylase, is a critical negative regulator of both the innate and adaptive immune response in mice, and its altered functions are likely to be involved in autoimmune diseases. Small molecules that modulate Sirt1 functions are potential therapeutic reagents for autoimmune inflammatory diseases. This review highlights the role of Sirt1 in immune regulation and RA.

Disruption of Sirt1 in chondrocytes causes accelerated progression of osteoarthritis under mechanical stress and during ageing in mice

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.

Sirt1-deficient mice exhibit an altered cartilage phenotype

OBJECTIVE

We previously demonstrated that Sirt1 regulates apoptosis in cartilage in vitro. Here we attempt to examine in vivo cartilage homeostasis, using Sirt1 total body knockout (KO) mice.

METHOD

Articular cartilage was harvested from hind paws of 1-week and 3-week-old mice carrying wild type (WT) or null Sirt1 gene. Knees of Sirt1 haploinsufficient mice also were examined, at 6 months. Joint cartilage was processed for histologic examination or biochemical analyses of chondrocyte cultures.

RESULTS

We found that articular cartilage tissue sections from Sirt1 KO mice up to 3 weeks of age exhibited low levels of type 2 collagen, aggrecan, and glycosaminoglycan content. In contrast, protein levels of MMP-13 were elevated in the Sirt1 KO mice, leading to a potential increase of cartilage breakdown, already shown in the heterozygous mice. Additional results showed elevated chondrocyte apoptosis in Sirt1 KO mice, as compared to WT controls. In addition to these observations, PTP1b (protein tyrosine phosphatase b) was elevated in the Sirt1 KO mice, in line with previous reports.

CONCLUSION

The findings from this animal model demonstrated that Sirt1 KO mice presented an altered cartilage phenotype, with an elevated apoptotic process and a potential degradative cartilage process.

Sirtuin 1 enzymatic activity is required for cartilage homeostasis in vivo in a mouse model

OBJECTIVE

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.

METHODS

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.

RESULTS

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.

CONCLUSION

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.

Chondroprotective and anti-inflammatory role of melanocortin peptides in TNF-α activated human C-20/A4 chondrocytes

BACKGROUND AND PURPOSE

Melanocortin MC(1) and MC(3 ) receptors, mediate the anti-inflammatory effects of melanocortin peptides. Targeting these receptors could therefore lead to development of novel anti-inflammatory therapeutic agents. We investigated the expression of MC(1) and MC(3) receptors on chondrocytes and the role of α-melanocyte-stimulating hormone (α-MSH) and the selective MC(3) receptor agonist, [DTRP(8) ]-γ-MSH, in modulating production of inflammatory cytokines, tissue-destructive proteins and induction of apoptotic pathway(s) in the human chondrocytic C-20/A4 cells.

EXPERIMENTAL APPROACH

Effects of α-MSH, [DTRP(8) ]-γ-MSH alone or in the presence of the MC(3/4) receptor antagonist, SHU9119, on TNF-α induced release of pro-inflammatory cytokines, MMPs, apoptotic pathway(s) and cell death in C-20/A4 chondrocytes were investigated, along with their effect on the release of the anti-inflammatory cytokine IL-10.

KEY RESULTS

C-20/A4 chondrocytes expressed functionally active MC(1,3) receptors. α-MSH and [DTRP(8) ]-γ-MSH treatment, for 30 min before TNF-α stimulation, provided a time-and-bell-shaped concentration-dependent decrease in pro-inflammatory cytokines (IL-1β, IL-6 and IL-8) release and increased release of the chondroprotective and anti-inflammatory cytokine, IL-10, whilst decreasing expression of MMP1, MMP3, MMP13 genes.α-MSH and [DTRP(8) ]-γ-MSH treatment also inhibited TNF-α-induced caspase-3/7 activation and chondrocyte death. The effects of [DTRP(8) ]-γ-MSH, but not α-MSH, were abolished by the MC(3/4) receptor antagonist, SHU9119.

CONCLUSION AND IMPLICATIONS

Activation of MC(1) /MC(3) receptors in C-20/A4 chondrocytes down-regulated production of pro-inflammatory cytokines and cartilage-destroying proteinases, inhibited initiation of apoptotic pathways and promoted release of chondroprotective and anti-inflammatory cytokines. Developing small molecule agonists to MC(1) /MC(3) receptors could be a viable approach for developing chondroprotective and anti-inflammatory therapies in rheumatoid and osteoarthritis.

Epigenetics, sirtuins and osteoarthritis

Epigenetics, modifications of the DNA other than changes on the DNA sequences, is frequently studied in cancer research and aging. DNA methylation, mi-RNA, and histones deacetylation are investigated in different pathologies, including inflammatory diseases and age-related diseases such as osteoarthritis (OA). In this review, we focus on the chromatin-modifying enzymes in arthritic pathologies, and more particularly on Sirtuins. We also review the role of Sirt1 in OA, which has been highlighted in recent publications, and examine the possible protective role Sirt1 could play in this disease. Moreover, we discuss the possible therapeutic target of such a protein, reviewing the potential inhibitors/activators of this enzyme and their properties.

Increased apoptotic chondrocytes in articular cartilage from adult heterozygous SirT1 mice

OBJECTIVE

A growing body of evidence indicates that the protein deacetylase, SirT1, affects chondrocyte biology and survival. This report aims to evaluate in vivo attributes of SirT1 in cartilage biology of 129/J murine strains.

METHODS

Heterozygous haploinsufficient (SirT1(+/-)) and wild-type (WT; SirT1(+/+)) 129/J mice aged 1 or 9 months were systematically compared for musculoskeletal features, scored for osteoarthritis (OA) severity, and monitored for chondrocyte apoptosis in articular cartilage. Sections of femorotibial joints were stained for type II collagen and aggrecan. Protein extracts from articular chondrocytes were isolated and immunoblotted for SirT1 and active caspase 3.

RESULTS

Phenotypic observations show that, at 1 month of age, SirT1(+/-) mice were smaller than WT and showed a significant decrease in full-length SirT1 (FLSirT1; 110 kDa) protein levels. Levels of FLSirT1 were further decreased in both strains at 9 months. Immunoblot assays for 9-month-old strains revealed the presence of the inactive cleaved SirT1 variant (75 SirT1; 75 kDa) in WT mice, which was undetected in age-matched SirT1(+/-) mice. Nine-month-old SirT1(+/-) mice also showed increased OA and increased levels of apoptosis compared with age-matched WT mice.

CONCLUSION

The data suggest that the presence of 75 SirT1 may prolong viability of articular chondrocytes in adult (9-month-old) mice.