Senp2 expression was induced by chronic glucose stimulation in INS1 cells, and it was required for the associated induction of Ccnd1 and Mafa

SENP2 regulates mitochondrial function and insulin secretion in pancreatic β cells

Increasing evidence has shown that small ubiquitin-like modifier (SUMO) modification plays an important role in metabolic regulation. We previously demonstrated that SUMO-specific protease 2 (SENP2) is involved in lipid metabolism in skeletal muscle and adipogenesis. In this study, we investigated the function of SENP2 in pancreatic β cells by generating a β cell-specific knockout (Senp2-βKO) mouse model. Glucose tolerance and insulin secretion were significantly impaired in the Senp2-βKO mice. In addition, glucose-stimulated insulin secretion (GSIS) was decreased in the islets of the Senp2-βKO mice without a significant change in insulin synthesis. Furthermore, islets of the Senp2-βKO mice exhibited enlarged mitochondria and lower oxygen consumption rates, accompanied by lower levels of S616 phosphorylated DRP1 (an active form of DRP1), a mitochondrial fission protein. Using a cell culture system of NIT-1, an islet β cell line, we found that increased SUMO2/3 conjugation to DRP1 due to SENP2 deficiency suppresses the phosphorylation of DRP1, which possibly induces mitochondrial dysfunction. In addition, SENP2 overexpression restored GSIS impairment induced by DRP1 knockdown and increased DRP1 phosphorylation. Furthermore, palmitate treatment decreased phosphorylated DRP1 and GSIS in β cells, which was rescued by SENP2 overexpression. These results suggest that SENP2 regulates mitochondrial function and insulin secretion at least in part by modulating the phosphorylation of DRP1 in pancreatic β cells.

SENP2 is vital for optimal insulin signaling and insulin-stimulated glycogen synthesis in human skeletal muscle cells

Sentrin-specific protease (SENP) 2 has been suggested as a possible novel drug target for the treatment of obesity and type 2 diabetes mellitus after observations of a palmitate-induced increase in SENP2 that lead to increased fatty acid oxidation and improved insulin sensitivity in skeletal muscle cells from mice. However, no precedent research has examined the role of SENP2 in human skeletal muscle cells. In the present work, we have investigated the impact of SENP2 on fatty acid and glucose metabolism as well as insulin sensitivity in human skeletal muscle using cultured primary human myotubes. Acute (4 ​h) oleic acid oxidation was reduced in SENP2-knockdown (SENP2-KD) cells compared to control cells, with no difference in uptake. After prelabeling (24 ​h) with oleic acid, total lipid content and incorporation into triacylglycerol was decreased, while incorporation into other lipids, as well as complete oxidation and β-oxidation was increased in SENP2-KD cells. Basal glucose uptake (i.e., not under insulin-stimulated conditions) was higher in SENP2-KD cells, whereas oxidation was similar to control myotubes. Further, basal glycogen synthesis was not different in SENP2-KD myotubes, but both insulin-stimulated glycogen synthesis and Akt^Ser473 phosphorylation was completely blunted in SENP2-KD cells. In conclusion, SENP2 plays an important role in fatty acid and glucose metabolism in human myotubes. Interestingly, it also appears to have a pivotal role in regulating myotube insulin sensitivity. Future studies should examine the role of SENP2 in regulation of insulin sensitivity in other tissues and in vivo, defining the potential for SENP2 as a drug target.

Effects of dietary carbohydrate sources on lipid metabolism and SUMOylation modification in the liver tissues of yellow catfish

Dysregulation in hepatic lipid synthesis by excess dietary carbohydrate intake is often relevant with the occurrence of fatty liver; therefore, the thorough understanding of the regulation of lipid deposition and metabolism seems crucial to search for potential regulatory targets. In the present study, we examined TAG accumulation, lipid metabolism-related gene expression, the enzyme activities of lipogenesis-related enzymes, the protein levels of transcription factors or genes involving lipogenesis in the livers of yellow catfish fed five dietary carbohydrate sources, such as glucose, maize starch, sucrose, potato starch and dextrin, respectively. Generally speaking, compared with other carbohydrate sources, dietary glucose promoted TAG accumulation, up-regulated lipogenic enzyme activities and gene expressions, and down-regulated mRNA expression of genes involved in lipolysis and small ubiquitin-related modifier (SUMO) modification pathways. Further studies found that sterol regulatory element binding protein 1 (SREBP1), a key transcriptional factor relevant to lipogenic regulation, was modified by SUMO1. Mutational analyses found two important sites for SUMOylation modification (K254R and K264R) in SREBP1. Mutant SREBP lacking lysine 264 up-regulated the transactivation capacity on an SREBP-responsive promoter. Glucose reduced the SUMOylation level of SREBP1 and promoted the protein expression of SREBP1 and its target gene stearoyl-CoA desaturase 1 (SCD1), indicating that SUMOylation of SREBP1 mediated glucose-induced hepatic lipid metabolism. Our study elucidated the molecular mechanism of dietary glucose increasing hepatic lipid deposition and found that the SREBP-dependent transactivation was regulated by SUMO1 modification, which served as a new target for the transcriptional programmes governing lipid metabolism.

Desumoylation of aggrecan and collagen II facilitates degradation via aggrecanases in IL-1β-mediated osteoarthritis

Background: Aggrecan plays a crucial role in the ability of tissues to withstand compressive loads during the pathological progression of osteoarthritis (OA). Progressive loss of aggrecan from cartilage may result in exposure of the collagen matrix and can lead to its disintegration by metalloproteases. Although aggrecanases are expressed constitutively in human chondrocytes, the degradation of aggrecan is induced by proinflammatory cytokines; however, little is known about the underlying mechanisms. Methods: Human primary chondrocytes from OA patients or healthy donors and human chondrogenic SW1353 cells were cultured and stimulated with IL-1β in vitro, the mRNA expressions and protein levels of MMP-13, ADAMTS-4, ADAMTS-5, SENP1, and SENP2 were determined using real time PCR and Western blot, respectively. The localizations of aggrecan and Col-II, as well as the SUMOylation modification of these proteins were analyzed using immunofluorescence and immunoprecipitation assays, respectively. Results: Our results showed that a proinflammatory cytokine interleukin-1β induced the OA model and desumoylation of aggrecan and collagen type II because the small ubiquitin-like modifier 2/3 (SUMO2/3) was co-localized with aggrecan and collagen type II proteins and interacted physically with them. Mechanistic studies have shown that knockdown of SUMO2/3 expression can significantly enhance the rate of degradation of aggrecan and collagen type II at both the mRNA and protein levels in the OA model. In addition, SUMO-specific protease 2 (SENP2) plays important roles in the desumoylation of aggrecan, while knockdown of SENP2 can protect aggrecan and collagen type II. Clinical assays have shown that OA patients have higher SENP2 levels than healthy controls, and the SENP2 level correlates negatively with both aggrecan and collagen type II levels. Conclusion: SENP2 desumoylates aggrecan and collagen type II proteins in the inflammation induced OA, and SENP2 expression correlates with OA progression.

Identification of 10 SUMOylation-Related Genes From Yellow Catfish Pelteobagrus fulvidraco, and Their Transcriptional Responses to Carbohydrate Addition in vivo and in vitro

SUMOylation is a kind of important post-translational modification. In the present study, we identified 10 key genes involved in SUMOylation and deSUMOylation (sumo1, sumo2, sumo3, sae1, uba2, ubc9, pias1, senp1, senp2, and senp3) in yellow catfish Pelteobagrus fulvidraco, investigated their tissue expression patterns and transcriptional responses to carbohydrate addition both in vivo and in vitro. All of these members shared similar domains to their orthologous genes of other vertebrates. Their mRNAs were widely expressed in all the tested tissues, but at variable levels. Dietary carbohydrate levels differentially influenced the mRNA levels of these genes in liver, muscle, testis, and ovary of yellow catfish. Their mRNA levels in primary hepatocytes were differentially responsive to glucose addition. Our study would contribute to our understanding into the molecular basis of SUMOylation modification and into the potential SUMOylation function in the carbohydrate utilization in fish.

SUMO1/sentrin/SMT3 specific peptidase 2 modulates target molecules and its corresponding functions

Small ubiquitin-like modifier (SUMOylation) is a reversible post-translational modification, which plays important roles in numerous biological processes. SUMO could be covalently attached to target proteins in an isopeptide bond manner that occurs via a lysine ε-amino group on the target proteins and the glycine on SUMO C-terminus. This covalent binding could affect the subcellular localization and stability of target proteins. SUMO modification can be reversed by members of the Sentrin/SUMO-specific proteases (SENPs) family, which are highly evolutionarily conserved from yeast to human. SENP2, a member of the SENPs family, mainly plays a physiological function in the nucleus. SENP2 can promote maturity of the SUMO and deSUMOylate for single-SUMO modified or poly-SUMO modified proteins. SENP2 can affect the related biological processes through its peptidase activity or the amino terminal transcriptional repression domain. It plays important roles by inhibiting or activating some molecular functions. Therefore, the research achievements of SENP2 are reviewed in order to understand its related functions and the underlying molecular mechanisms and provide a clue for future research on SENP2.