PEP-1-SIRT2-induced matrix metalloproteinase-1 and -13 modulates type II collagen expression via ERK signaling in rabbit articular chondrocytes

Sirtuins in intervertebral disc degeneration: current understanding

BACKGROUND

Intervertebral disc degeneration (IVDD) is one of the etiologic factors of degenerative spinal diseases, which can lead to a variety of pathological spinal conditions such as disc herniation, spinal stenosis, and scoliosis. IVDD is a leading cause of lower back pain, the prevalence of which increases with age. Recently, Sirtuins/SIRTs and their related activators have received attention for their activity in the treatment of IVDD. In this paper, a comprehensive systematic review of the literature on the role of SIRTs and their activators on IVDD in recent years is presented. The molecular pathways involved in the regulation of IVDD by SIRTs are summarized, and the effects of SIRTs on senescence, inflammatory responses, oxidative stress, and mitochondrial dysfunction in myeloid cells are discussed with a view to suggesting possible solutions for the current treatment of IVDD.

PURPOSE

This paper focuses on the molecular mechanisms by which SIRTs and their activators act on IVDD.

METHODS

A literature search was conducted in Pubmed and Web of Science databases over a 13-year period from 2011 to 2024 for the terms "SIRT", "Sirtuin", "IVDD", "IDD", "IVD", "NP", "Intervertebral disc degeneration", "Intervertebral disc" and "Nucleus pulposus".

RESULTS

According to the results, SIRTs and a large number of activators showed positive effects against IVDD.SIRTs modulate autophagy, myeloid apoptosis, oxidative stress and extracellular matrix degradation. In addition, they attenuate inflammatory factor-induced disc damage and maintain homeostasis during disc degeneration. Several clinical studies have reported the protective effects of some SIRTs activators (e.g., resveratrol, melatonin, honokiol, and 1,4-dihydropyridine) against IVDD.

CONCLUSION

The fact that SIRTs and their activators play a hundred different roles in IVDD helps to better understand their potential to develop further treatments for IVDD.

NOVELTY

This review summarizes current information on the mechanisms of action of SIRTs in IVDD and the challenges and limitations of translating their basic research into therapy.

Cysteine thiol oxidation on SIRT2 regulates inflammation in obese mice with sepsis

Obesity increases morbidity and mortality in acute illnesses such as sepsis and septic shock. We showed previously that the early/hyper-inflammatory phase of sepsis is exaggerated in obese mice with sepsis; sirtuin 2 (SIRT2) modulates sepsis inflammation in obesity. Evidence suggests that obesity with sepsis is associated with increased oxidative stress. It is unknown whether exaggerated hyper-inflammation of obesity with sepsis modulates the SIRT2 function in return. We showed recently that SIRT6 oxidation during hyper-inflammation of sepsis modulates its glycolytic function. This study tested the hypothesis that increased oxidative stress and direct SIRT2 oxidation exaggerate hyper-inflammation in obesity with sepsis. Using spleen and liver tissue from mice with diet-induced obesity (DIO) we studied oxidized vs. total SIRT2 expression during hyper- and hypo-inflammation of sepsis. To elucidate the mechanism of SIRT2 oxidation (specific modifications of redox-sensitive cysteines) and its effect on inflammation, we performed site-directed mutations of redox-sensitive cysteines Cys221 and Cys224 on SIRT2 to serine (C221S and C224S), transfected HEK293 cells with mutants or WT SIRT2, and studied SIRT2 enzymatic activity and NFĸBp65 deacetylation. Finally, we studied the effect of SIRT2 mutation on LPS-induced inflammation using RAW 264.7 macrophages. In an inverse relationship, total SIRT2 decreased while oxidized SIRT2 expression increased during hyper-inflammation and SIRT2 was unable to deacetylate NFĸBp65 with increased oxidative stress of obesity with sepsis. Mechanistically, both the mutants (C221S and C224S) show decreased (1) SIRT2 enzymatic activity, (2) deacetylation of NFĸBp65, and (3) anti-inflammatory activity in response to LPS vs. WT SIRT2. Direct oxidation modulates SIRT2 function during hyper-inflammatory phase of obesity with sepsis via redox sensitive cysteines.

SIRT2, ERK and Nrf2 Mediate NAD+ Treatment-Induced Increase in the Antioxidant Capacity of PC12 Cells Under Basal Conditions

NAD⁺ (oxidized form of nicotinamide adenine dinucleotide) administration is highly beneficial in numerous models of diseases and aging. It is becoming increasingly important to determine if NAD⁺ treatment may directly increase the antioxidant capacity of cells under basal conditions. In the current study, we tested our hypothesis that NAD⁺ can directly enhance the antioxidant capacity of cells under basal conditions by using PC12 cells as a cellular model. We found that NAD⁺ treatment can increase the GSH/GSSG ratios in the cells under basal conditions. NAD⁺ can also increase both the mRNA and protein level of γ-glutamylcysteine ligase (γ-GCL)—a key enzyme for glutathione synthesis, which appears to be mediated by the NAD⁺-induced increase in Nrf2 activity. These NAD⁺-induced changes can be prevented by both SIRT2 siRNA and the SIRT2 inhibitor AGK2. The NAD⁺-induced changes can also be blocked by the ERK signaling inhibitor U0126. Moreover, the NAD⁺-induced ERK activation can be blocked by both SIRT2 siRNA and AGK2. Collectively, our study has provided the first evidence that NAD⁺ can enhance directly the antioxidant capacity of the cells under basal conditions, which is mediated by SIRT2, ERK, and Nrf2. These findings have suggested not only the great nutritional potential of NAD⁺, but also a novel mechanism underlying the protective effects of the NAD⁺ administration in the disease models: the NAD⁺ administration can enhance the resistance of the normal cells to oxidative insults by increasing the antioxidant capacity of the cells.

Current understanding and future perspectives of the roles of sirtuins in the reprogramming and differentiation of pluripotent stem cells

In mammalian cells, there are seven members of the sirtuin protein family (SIRT1-7). SIRT1, SIRT6, and SIRT7 catalyze posttranslational modification of proteins in the nucleus, SIRT3, SIRT4, and SIRT5 are in the mitochondria and SIRT2 is in the cytosol. SIRT1 can deacetylate the transcription factor SOX2 and regulate induced pluripotent stem cells (iPSCs) reprogramming through the miR-34a-SIRT1-p53 axis. SIRT2 can regulate the function of pluripotent stem cells through GSK3β. SIRT3 can positively regulate PPAR gamma coactivator 1-alpha (PGC-1α) expression during the differentiation of stem cells. SIRT4 has no direct role in regulating reprogramming but may have the potential to prevent senescence of somatic cells and to facilitate the reprogramming of iPSCs. SIRT5 can deacetylate STAT3, which is an important transcription factor in regulating pluripotency and differentiation of stem cells. SIRT6 can enhance the reprogramming efficiency of iPSCs from aged skin fibroblasts through miR-766 and increase the expression levels of the reprogramming genes including Sox2, Oct4, and Nanog through acetylation of histone H3 lysine 56. SIRT7 plays a regulatory role in the process of mesenchymal-to-epithelial transition (MET), which has been suggested to be a crucial process in the generation of iPSCs from fibroblasts. In this review, we summarize recent findings of the roles of sirtuins in the metabolic reprogramming and differentiation of stem cells and discuss the bidirectional changes in the gene expression and activities of sirtuins in the commitment of differentiation of mesenchymal stem cells (MSCs) and reprogramming of somatic cells to iPSCs, respectively. Thus, understanding the molecular basis of the interplay between different sirtuins and mitochondrial function will provide new insights into the regulation of differentiation of stem cells and iPSCs formation, respectively, and may help design effective stem cell therapies for regenerative medicine. Impact statement This is an extensive review of the recent advances in our understanding of the roles of some members of the sirtuins family, such as SIRT1, SIRT2, SIRT3, and SIRT6, in the regulation of intermediary metabolism during stem cell differentiation and in the reprogramming of somatic cells to form induced pluripotent stem cells (iPSCs). This article provides an updated integrated view on the mechanisms by which sirtuins-mediated posttranslational protein modifications regulate mitochondrial biogenesis, bioenergetics, and antioxidant defense in the maintenance and differentiation of stem cells and in iPSCs formation, respectively.

Rosmarinic acid induces rabbit articular chondrocyte differentiation by decreases matrix metalloproteinase-13 and inflammation by upregulating cyclooxygenase-2 expression

BACKGROUND

Matrix metalloproteinases (MMPs) are known to play an important role in the degradation of the extracellular matrix and the pathological progression of osteoarthritis (OA). The natural polyphenolic compound rosmarinic acid (Ros. A) has been shown to suppress the inhibitory activity of matrix metalloproteinases (MMPs). However, the effects of Ros. A on OA have not been investigated.

METHODS

In the current study, primary articular chondrocytes were cultured from rabbit articular cartilage and treated with Ros. A. Phenotypic characterization was performed by western blotting to assess specific markers, prostaglandin E2 (PGE2) assays, and alcian blue staining to measure sulfated-proteoglycan production.

RESULTS

We report that in rabbit articular chondrocytes, Ros. A increased type II collagen, sulfated-proteoglycan, cyclooxygenase-2 (COX-2), and PGE2 production in a dose- and time-dependent manner. Furthermore, Ros. A suppressed the expression of MMP-13. In addition, treatment with Ros A activated extracellular signal-regulated kinase (ERK)-1/2 and p38 kinase signaling pathways. Inhibition of MMP-13 enhanced Ros. A-induced type II collagen expression and sulfated-proteoglycan synthesis but COX-2 and PGE2 production were unchanged. Ros. A-mediated up-regulation of ERK phosphorylation was abolished by the MEK inhibitor, PD98059, which prevented induction of the associated inflammatory response. Inhibition of p38 kinase with SB203580 enhanced the increase in type II collagen expression via Ros. A-mediated down-regulation of MMP-13.

CONCLUSIONS

Results suggest that ERK-1/2 regulates Ros. A-induced inflammation and that p38 regulates differentiation by inhibiting MMP-13 in rabbit articular chondrocytes.

Sirtuin 6 prevents matrix degradation through inhibition of the NF-κB pathway in intervertebral disc degeneration

Intervertebral disc degeneration (IDD) is marked by imbalanced metabolism of the extracellular matrix (ECM) in the nucleus pulposus (NP) of intervertebral discs. This study aimed to determine whether sirtuin 6 (SIRT6), a member of the sirtuin family of nicotinamide adenine dinucleotide-dependent deacetylases, protects the NP from ECM degradation in IDD. Our study showed that expression of SIRT6 markedly decreased during IDD progression. Overexpression of wild-type SIRT6, but not a catalytically inactive mutant, prevented IL-1β-induced NP ECM degradation. SIRT6 depletion by RNA interference in NP cells caused ECM degradation. Moreover, SIRT6 physically interacted with nuclear factor-κB (NF-κB) catalytic subunit p65, transcriptional activity of which was significantly suppressed by SIRT6 overexpression. These results suggest that SIRT6 prevented NP ECM degradation in vitro via inhibiting NF-κB-dependent transcriptional activity and that this effect depended on its deacetylase activity.