PEP-1-SIRT2 causes dedifferentiation and COX-2 expression via the MAPK pathways in rabbit articular chondrocytes

Context-dependent role of sirtuin 2 in inflammation

Sirtuin 2 is a member of the sirtuin family nicotinamide adenine dinucleotide (NAD+)-dependent deacetylases, known for its regulatory role in different processes, including inflammation. In this context, sirtuin 2 has been involved in the modulation of key inflammatory signaling pathways and transcription factors by deacetylating specific targets, such as nuclear factor κB and nucleotide-binding oligomerization domain-leucine-rich-repeat and pyrin domain-containing protein 3 (NLRP3). However, whether sirtuin 2-mediated pathways induce a pro- or an anti-inflammatory response remains controversial. Sirtuin 2 has been implicated in promoting inflammation in conditions such as asthma and neurodegenerative diseases, suggesting that its inhibition in these conditions could be a potential therapeutic strategy. Conversely, arthritis and type 2 diabetes mellitus studies suggest that sirtuin 2 is essential at the peripheral level and, thus, its inhibition in these pathologies would not be recommended. Overall, the precise role of sirtuin 2 in inflammation appears to be context-dependent, and further investigation is needed to determine the specific molecular mechanisms and downstream targets through which sirtuin 2 influences inflammatory processes in various tissues and pathological conditions. The present review explores the involvement of sirtuin 2 in the inflammation associated with different pathologies to elucidate whether its pharmacological modulation could serve as an effective strategy for treating this prevalent symptom across various diseases.

Sirtuin family in autoimmune diseases

In recent years, epigenetic modifications have been widely researched. As humans age, environmental and genetic factors may drive inflammation and immune responses by influencing the epigenome, which can lead to abnormal autoimmune responses in the body. Currently, an increasing number of studies have emphasized the important role of epigenetic modification in the progression of autoimmune diseases. Sirtuins (SIRTs) are class III nicotinamide adenine dinucleotide (NAD)-dependent histone deacetylases and SIRT-mediated deacetylation is an important epigenetic alteration. The SIRT family comprises seven protein members (namely, SIRT1-7). While the catalytic core domain contains amino acid residues that have remained stable throughout the entire evolutionary process, the N- and C-terminal regions are structurally divergent and contribute to differences in subcellular localization, enzymatic activity and substrate specificity. SIRT1 and SIRT2 are localized in the nucleus and cytoplasm. SIRT3, SIRT4, and SIRT5 are mitochondrial, and SIRT6 and SIRT7 are predominantly found in the nucleus. SIRTs are key regulators of various physiological processes such as cellular differentiation, apoptosis, metabolism, ageing, immune response, oxidative stress, and mitochondrial function. We discuss the association between SIRTs and common autoimmune diseases to facilitate the development of more effective therapeutic strategies.

Multiple Roles of SIRT2 in Regulating Physiological and Pathological Signal Transduction

Sirtuin 2 (SIRT2), as a member of the sirtuin family, has representative features of evolutionarily highly conserved nicotinamide adenine dinucleotide (NAD+)-dependent deacetylase activity. In addition, SIRT2, as the only sirtuin protein colocalized with tubulin in the cytoplasm, has its own functions and characteristics. In recent years, studies have increasingly shown that SIRT2 can participate in the regulation of gene expression and regulate signal transduction in the metabolic pathway mainly through its post-translational modification of target genes; thus, SIRT2 has become a key centre in the metabolic pathway and participates in the pathological process of metabolic disorder-related diseases. In this paper, it is discussed that SIRT2 can regulate all aspects of gene expression, including epigenetic modification, replication, transcription and translation, and post-translational modification, which enables SIRT2 to participate in energy metabolism in life activities, and it is clarified that SIRT2 is involved in metabolic process-specific signal transduction mechanisms. Therefore, SIRT2 can be involved in metabolic disorder-related inflammation and oxidative stress, thereby triggering the occurrence of metabolic disorder-related diseases, such as neurodegenerative diseases, tumours, diabetes, and cardiovascular diseases. Currently, although the role of SIRT2 in some diseases is still controversial, given the multiple roles of SIRT2 in regulating physiological and pathological signal transduction, SIRT2 has become a key target for disease treatment. It is believed that with increasing research, the clinical application of SIRT2 will be promoted.

Identification of proteins associated with development of psoriatic arthritis in peripheral blood mononuclear cells: a quantitative iTRAQ-based proteomics study

Background

Biomarkers for distinguishing psoriatic arthritis (PsA) from psoriasis without arthritis (PsO) are still lacking.

Methods

We applied isobaric tags for relative and absolute quantification (iTRAQ) and LC–MS/MS to analyze the proteome profile of peripheral blood mononuclear cells (PBMCs) collected from patients with PsO, patients with PsA, and healthy controls. Bioinformatics analysis and western blotting were performed to identify and validate differentially expressed proteins.

Results

We identified 389, 199, 291, and 60 significantly differentially expressed proteins (adj.p < 0.05) in the comparison of all psoriatic patients versus healthy controls, PsO group versus healthy controls, PsA group versus healthy controls, and PsA group versus PsO group, respectively. Among these proteins, 14 proteins may represent promising biomarkers for PsA: SIRT2, NAA50, ARF6, ADPRHL2, SF3B6, SH3KBP1, UBA3, SCP2, RPS5, NUDT5, NCBP1, SYNE1, NDUFB7, HTATSF1. Furthermore, western blotting confirmed that SIRT2 expression was significantly higher in PBMCs from PsA patients than PsO and healthy controls, and was negatively correlated with the phosphorylation of p38 mitogen-activated protein kinase (p-p38MAPK; p = 0.006, r = − 0.582).

Conclusions

This pilot study provided a broad characterization of the proteome of PBMCs in PsA as compared to PsO and healthy controls, which may help to provide prospective strategies for PsA diagnosis.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12967-021-03006-x.

Three-dimensional (3D) hydrogel serves as a platform to identify potential markers of chondrocyte dedifferentiation by combining RNA sequencing

Dedifferentiation of chondrocyte greatly restricts its function and application, however, it is poorly understood except a small number of canonical markers. The non-cell-adhesive property endows polysaccharide hydrogel with the ability to maintain chondrocyte phenotype, which can serve as a platform to identify new molecular markers and therapeutic targets of chondrocyte dedifferentiation. In this study, the high-throughput RNA sequencing (RNA-seq) was first performed on articular chondrocytes at primary (P0) and passage 1 (P1) stages to explore the global alteration of gene expression along with chondrocyte dedifferentiation. Significantly, several potential marker genes, such as PFKFB3, KDM6B, had been identified via comparatively analyzing their expression in P0 and P1 chondrocytes as well as in 3D constructs (i.e. chondrocyte-laden alginate hydrogel and HA-MA hydrogel) at both mRNA and protein level. Besides, the changes in cellular morphology and enriched pathway of differentially expressed genes during chondrocyte dedifferentiation was studied in detail. This study developed the use of hydrogel as a platform to investigate chondrocyte dedifferentiation; the results provided new molecular markers and potential therapeutic targets of chondrocyte dedifferentiation.

Overexpression of sirtuin 2 and its association with prognosis in acute ischemic stroke patients

Background

This study aimed to investigate the correlation of sirtuin 2 (SIRT2) with acute ischemic stroke (AIS) risk, severity, inflammation, and prognosis.

Methods

A hundred and sixty‐four first episode AIS patients and 164 age and gender matched non‐AIS patients with high‐stroke‐risk factors (controls) were enrolled. Peripheral blood was collected and serum was separated for SIRT2 and pro‐inflammatory cytokines detection by enzyme‐linked immunosorbent assay. AIS patients were continually followed up to 36 months or death, then recurrence‐free survival (RFS) and overall survival (OS) were calculated.

Results

Serum SIRT2 expression was increased in AIS patients compared to controls (p < 0.001), then receiver operative characteristic curve disclosed that the serum SIRT2 expression could differentiate AIS patients from controls with a good area under curve of 0.890 (95%CI: 0.854–0.926), a sensitivity of 78.7% and a specificity of 91.5% at the best cut‐off point. Serum SIRT2 expression was positively correlated with National Institute of Health stroke scale score (p < 0.001), serum tumor necrosis factor‐α (p < 0.001), interleukin (IL)‐6 (p = 0.012) and IL‐17 (p < 0.001) expressions in AIS patients. In addition, serum SIRT2 expression was elevated in recurrent/dead AIS patients compared to non‐recurrent/dead AIS patients (p = 0.025), and was also increased in dead AIS patients compared to survivors (p = 0.006). Moreover, RFS (p = 0.029) and OS (p = 0.049) were both worse in AIS patients with SIRT2 high expression compared to AIS patients with SIRT2 low expression.

Conclusion

SIRT2 may serve as a marker for AIS risk and prognosis in clinical practice.

Dedifferentiation: inspiration for devising engineering strategies for regenerative medicine

Cell dedifferentiation is the process by which cells grow reversely from a partially or terminally differentiated stage to a less differentiated stage within their own lineage. This extraordinary phenomenon, observed in many physiological processes, inspires the possibility of developing new therapeutic approaches to regenerate damaged tissue and organs. Meanwhile, studies also indicate that dedifferentiation can cause pathological changes. In this review, we compile the literature describing recent advances in research on dedifferentiation, with an emphasis on tissue-specific findings, cellular mechanisms, and potential therapeutic applications from an engineering perspective. A critical understanding of such knowledge may provide fresh insights for designing new therapeutic strategies for regenerative medicine based on the principle of cell dedifferentiation.

Gallotannin attenuates 2‑deoxy‑D‑glucose‑induced dedifferentiation and endoplasmic reticulum stress through inhibition of inositol‑requiring enzyme 1 downstream p38 kinase pathway in chondrocytes

Gallotannin (GT) is a class of polyphenols with antioxidant, anticancer, and antiviral activities. 2‑Deoxy‑D‑glucose (2DG), a glucose‑derived molecule, can inhibit glucose metabolism and induce endoplasmic reticulum (ER) stress. GT in primary‑cultured chondrocytes enhances expression of type II collagen, an indicator of differentiation, and cyclooxygenase‑2 (COX‑2), which mediates inflammatory reactions. In contrast, 2DG reduces type II collagen and COX‑2 expression while driving ER‑stress‑induced unglycosylation. In the present study, it was investigated whether GT could attenuate 2DG‑induced dedifferentiation and ER‑stress. Following treatment with GT and 2DG, chondrocytes were assessed using western blotting, RT‑PCR, immunofluorescence, and alcian blue staining. GT restored type II collagen expression that was reduced by 2DG, inhibited ER‑stress‑induced COX‑2 unglycosylation, and induced COX‑2 expression. The expression of a glucose‑regulated protein, GRP78, which is an indicator of reduced ER‑stress, was decreased. To link the GT signaling pathway with pathways that inhibit 2DG‑induced dedifferentiation and ER‑stress, inhibitors were treated in chondrocytes. The results revealed that, among the different signaling pathways triggered by ER‑stress, the p38 kinase pathway was involved in the inositol‑requiring enzyme 1 (IRE1) downstream signaling pathway. Following inhibition of the IRE1 pathway, type II collagen expression was increased and COX‑2 expression was decreased. In addition, after examining the splicing of X‑box binding protein 1 (XBP‑1) which is dependent on IRE1 activation induced by ER‑stress, it was revealed that GT inhibited the increase of XBP‑1s after splicing due to 2DG‑induced ER stress. GT in chondrocytes inhibited 2DG‑induced dedifferentiation and ER‑stress‑induced COX‑2 unglycosylation while regulating differentiation and inflammation via the ER‑stress‑induced p38 kinase pathway downstream from the IRE1 pathway.

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.

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.

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

Matrix metalloproteinases (MMPs) are critical for the degradation of the extracellular matrix (ECM), which includes cartilage-specific collagen types I, II and XI. We previously found that PEP-1-sirtuin (SIRT)2 could induce dedifferentiation of articular chondrocytes; however, the underlying mechanisms remains unclear. We addressed this in the present study by examining the association between PEP-1-SIRT2 and the expression of MMP-1 and MMP-13 and type II collagen in rabbit articular chondrocytes. We found that PEP-1-SIRT2 increased MMP-1 and -13 expression in a dose- and time-dependent manner, as determined by western blotting. A similar trend in MMP-1 and -13 levels was observed in cultures during expansion to four passages. Pharmacological inhibition of MMP-1 and -13 blocked the PEP-1-SIRT2-induced decrease in type II collagen level. Phosphorylation of extracellular regulated kinase (ERK) was increased by PEP-1-SIRT2; however, treatment with the mitogen-activated protein kinase inhibitor PD98059 suppressed PEP-1-SIRT2-induced MMP-1 and -13 expression and dedifferentiation while restoring type II collagen expression in passage 2 cells. These results suggest that PEP-1-SIRT2 promotes MMP-induced dedifferentiation via ERK signaling in articular chondrocytes.