小泛素样修饰蛋白特异性蛋白酶1介导糖尿病性血管内皮细胞损伤修复的研究

目的利用小泛素相关修饰体(SUMO)特异性蛋白酶1(SENP1)解离过氧化物酶体增殖物激活受体γ辅激活因子1α(PGC-1α)的小泛素样修饰蛋白1(SUMO1)修饰。方法人脐静脉内皮细胞培养传代后分对照组、高糖组及SENP1组;Western blot法检测SENP1、SUMO1、PGC-1α和半胱氨酸天冬氨酸蛋白酶3(Caspase-3)水平;实时荧光定量PCR检测线粒体转录因子A(TFAM)、核呼吸因子2α(NRF-2α)和雌激素受体相关受体α(ERRα)的mRNA表达;ELISA测定乳酸脱氢酶(LDH);细胞划痕愈合方法、Transwell方法和体外血管模拟形成实验分别检测细胞自愈、迁移和形成血管拟态的能力。结果与对照组比较,高糖组共价SUMO1、PGC-1α和活化Caspase-3蛋白表达明显升高,SENP1蛋白表达明显降低,TFAM、NRF-2α和ERRα的mRNA表达明显降低,细胞划痕修复能力及模拟血管形成能力下降(P<0.05,P<0.01)。与高糖组比较,SENP1组SENP1蛋白表达明显升高,共价SUMO1、PGC-1α和活化Caspase-3蛋白表达明显降低,TFAM、NRF-2α和ERRα的mRNA表达明显升高,细胞划痕修复和迁移能力及模拟血管形成能力明显改善(P<0.05,P<0.01)。对照组、高糖组和SENP1组细胞上清液中LDH水平比较,差异有统计学意义[(24.66±6.39)ng/ml vs(302.45±30.54)ng/ml vs(174.08±21.03)ng/ml,P<0.01]。结论SENP1能够诱导PGC-1α发生去SUMO修饰,解除其对PGC-1α下游转录因子的抑制作用,改善线粒体功能,抑制高糖诱导的血管内皮细胞功能损伤作用。     

One SUMO is sufficient to silence the dimeric potassium channel K2P1

Small ubiquitin modifier 1 (SUMO1) is shown to regulate K2P1 background channels in the plasma membrane (PM) of live mammalian cells. Confocal microscopy reveals native SUMO1, SAE1, and Ubc9 (the enzymes that activate and conjugate SUMO1) at PM where SUMO1 and expressed human K2P1 are demonstrated to colocalize. Silent K2P1 channels in excised PM patches are activated by SUMO isopeptidase (SENP1) and resilenced by SUMO1. K2P1-Lys274 is crucial: when mutated to Gln, Arg, Glu, Asp, Cys, or Ala, the channels are constitutively active and insensitive to SUMO1 and SENP1. Tandem mass spectrometry confirms conjugation of SUMO1 to the ε-amino group of Lys274 in vitro. FRET microscopy shows that assembly of K2P1 and SUMO1 requires Lys274. Single-particle TIRF microscopy shows that wild-type channels in PM have two K2P1 subunits and assemble with two SUMO1 monomers. Although channels engineered with one Lys274 site carry just one SUMO1 they are activated and silenced by SENP1 and SUMO1 like wild-type channels.     

C2株蓝氏贾第鞭毛虫SUMO特异性蛋白酶基因的克隆、生物信息学分析及其催化活性区的原核表达

目的 克隆C2株蓝氏贾第鞭毛虫(Giardia lamblia,简称贾第虫)的SUMO-Specific Protease(SENP)基因,并对其序列进行生物信息学分析,原核表达贾第虫SENP的催化活性区。方法 提取C2株贾第虫基因组DNA,以基因组DNA为模板获得SENP编码区全长片段,连入克隆载体pGM-T,测序后进行生物信息学分析;根据分析结果克隆SENP的催化活性区,构建其原核表达载体pET-28a(+)-SENPc,在E.coli Rosetta(DE3)中诱导表达,SDS-PAGE及Western blot观察表达结果。结果 成功克隆了C2株贾第虫SENP编码区全长序列,生物信息学分析显示C2株贾第虫SENP蛋白序列与WB株相同,二级结构以无规则卷曲为主,其催化活性区位于126-497aa,被一段插入序列分割成两个部分;构建了SENP催化活性区原核表达载体并在大肠杆菌中高效表达,在相对分子量约43 kD的位置出现目的 蛋白条带,与理论值相符。结论 成功克隆了贾第虫SENP基因并原核表达了其催化活性区,为贾第虫SENP蛋白功能的研究提供了基础。     

Human proinsulin C-peptide prevents proliferation of rat aortic smooth muscle cells cultured in high-glucose conditions

Aims/hypothesis Proinsulin C-peptide is involved in several biological activities. However, the role of C-peptide in vascular smooth muscle cells is unclear. We therefore investigated its effects, in vascular smooth muscle cells in high-glucose conditions.Methods Rat aortic smooth muscle cells were cultured with 5.5 or 20 mmol/l glucose with or without C-peptide (1 to 100 nmol/l) for 3 weeks. Proliferation activities, the protein expression of platelet-derived growth factor (PDGF)-beta receptor, the phosphorylation of p42/p44 mitogen-activated protein (MAP) kinases, and glucose uptake were measured.Results The proliferation activities increased approximately three-fold under high-glucose conditions (p<0.05). C-peptide suppressed hyperproliferation activities that were induced by high glucose. This happened in a dose-dependent manner from 1 to 100 nmol/l of C-peptide. C-peptide (10 and 100 nmol/l) inhibited the increased protein expression of PDGF-beta receptor and the phosphorylation of p42/p44 MAP kinases that had been induced by high glucose (p<0.05). Furthermore, 100 nmol/l of C-peptide augmented the impaired glucose uptake in the high-glucose conditions.Conclusions/interpretation These observations suggest that C-peptide could prevent diabetic macroangiopathy by inhibiting smooth muscle cell growth and ameliorating glucose utilisation in smooth muscle cells. C-peptide may thus be a novel agent for treating diabetic macroangiopathy in patients with type 1 and type 2 diabetes.     

The small ubiquitin‐like modifier mediates the resistance of prosthesis‐loosening fibroblast‐like synoviocytes against fas‐induced apoptosis

Objective

To study the expression of small ubiquitin‐like modifier 1 (SUMO‐1) in aseptic loosening of prosthesis implants and to investigate its role in regulating the susceptibility of prosthesis‐loosening fibroblast‐like synoviocytes (FLS) to Fas‐induced apoptosis.

Methods

Specimens of aseptically loosened tissue were obtained at revision surgery, and the expression of SUMO‐1 was analyzed by in situ hybridization. SUMO‐1 levels in FLS were determined by quantitative polymerase chain reaction and Western blot analysis. Immunohistochemistry and confocal microscopy were used to study the subcellular localization of SUMO‐1. The functional role of SUMO‐1 in Fas‐induced apoptosis of prosthesis‐loosening FLS was investigated by small interfering RNA–mediated knockdown of SUMO‐1 and by gene transfer of the nuclear SUMO‐specific protease SENP1.

Results

SUMO‐1 was expressed strongly in aseptically loosened tissue and was found prominently at sites adjacent to bone. Prosthesis‐loosening FLS expressed levels of SUMO‐1 similar to the levels expressed by rheumatoid arthritis (RA) FLS, with SUMO‐1 being found mainly in promyelocytic leukemia protein nuclear bodies. Knockdown of SUMO‐1 had no effect on spontaneous apoptosis but significantly increased the susceptibility of prosthesis‐loosening FLS to Fas‐induced apoptosis. Gene transfer of the nuclear SUMO‐specific protease SENP1 reverted the apoptosis‐inhibiting effects of SUMO‐1.

Conclusion

These data suggest that SUMO‐1 is involved in the activation of both RA FLS and prosthesis‐loosening FLS by preventing these cells from undergoing apoptosis. Modification of nuclear proteins by SUMO‐1 contributes to the antiapoptotic effects of SUMO‐1 in prosthesis‐loosening FLS, providing evidence for the specific activation of sumoylation during their differentiation. Therefore, SUMO‐1 may be an interesting target for novel strategies to prevent aseptic prosthesis loosening.

     

Autophagy deficiency in β cells blunts incretin-induced suppression of glucagon release from α cells

Incretin-based therapy such as GLP-1 receptor agonists and DPP-4 inhibitors for type 2 diabetes mellitus is characterized by glucose-dependent insulin secretion and glucose-inhibited glucagon secretion. Recently, autophagy deficiency in islet β cells has been shown to contribute to the pathogenesis of type 2 diabetes mellitus however, with the role of incretin has not been established. To evaluate the role of autophagy in incretin effects, 8-week-old male β cell-specific Atg7 knockout (Atg7^{Δβ cell}) mice and wild-type mice were administered vildagliptin for 12 weeks. Vildagliptin treatment improved glucose intolerance and hypoinsulinemia; however, it failed to suppress serum glucagon levels after glucose loading in the Atg7^{Δβ cell} mice. Ex vivo glucose-induced glucagon suppression was also blunted in the islets from vildagliptin-treated Atg7^{Δβ cell} mice. The α cell mass was not affected by β cell autophagy deficiency or vildagliptin. However, glucagon mRNA expression was significantly increased by vildagliptin in the autophagy-deficient islets, and was significantly reduced by vildagliptin in wild-type islets. Pancreatic glucagon contents were not in agreement with the changes in mRNA expression, suggesting a dysregulation in glucagon translation and secretion. In vitro studies revealed that glucose-stimulated cAMP production was impaired in the autophagy-deficient islets exposed to exendin-4. Taken together, the results suggest that the constitutive autophagy in β cells could regulate incretin-induced glucagon expression and release in α cells, and that cAMP may play a role in this process.     

Enhanced desumoylation in murine hearts by overexpressed SENP2 leads to congenital heart defects and cardiac dysfunction

Sumoylation is a posttranslational modification implicated in a variety of cellular activities, and its role in a number of human pathogeneses such as cleft lip/palate has been well documented. However, the importance of the SUMO conjugation pathway in cardiac development and functional disorders is newly emerging. We previously reported that knockout of SUMO-1 in mice led to congenital heart diseases (CHDs). To further investigate the effects of imbalanced SUMO conjugation on heart development and function and its underlying mechanisms, we generated transgenic (Tg) mice with cardiac-specific expression of SENP2, a SUMO-specific protease that deconjugates sumoylated proteins, to evaluate the impact of desumoylation on heart development and function. Overexpression of SENP2 resulted in premature death of mice with CHDs-atrial septal defects (ASDs) and/or ventricular septal defects (VSDs). Immunobiochemistry revealed diminished cardiomyocyte proliferation in SENP2-Tg mouse hearts compared with that in wild type (WT) hearts. Surviving SENP2-Tg mice showed growth retardation, and developed cardiomyopathy with impaired cardiac function with aging. Cardiac-specific overexpression of the SUMO-1 transgene reduced the incidence of cardiac structural phenotypes in the sumoylation defective mice. Moreover, cardiac overexpression of SENP2 in the mice with Nkx2.5 haploinsufficiency promoted embryonic lethality and severity of CHDs, indicating the functional interaction between SENP2 and Nkx2.5 in vivo. Our findings indicate the indispensability of a balanced SUMO pathway for proper cardiac development and function. This article is part of a Special Issue entitled 'Post-translational Modification SI'.     

RORB and RORC associate with human islet dysfunction and inhibit insulin secretion in INS-1 cells

Little is known about the expression and function of Retinoic acid-related orphan receptors (RORA, B, and C) in pancreatic β cells. Here in, we utilized cDNA microarray and RNA sequencing approaches to investigate the expression pattern of ROR receptors in normal and diabetic human pancreatic islets. Possible correlations between RORs expression and HbA_1c levels as well as insulin secretory capacity in isolated human islets were evaluated. The impact of RORB and RORC expression on insulin secretion in INS-1 (832/13) cells was validated as well. While RORA was the highest expressed gene among the three RORs in human islet cells, RORC was the highest expressed in INS-1 cells (832/13) and while RORB was the lowest expressed gene in human islet cells, RORA was the highest expressed in INS-1 cells (832/13). The expression of RORB and RORC was significantly lower in diabetic/hyperglycemic donors as compared with non-diabetic counterparts. Furthermore, while the expression of RORB correlated positively with insulin secretion and negatively with HbA_1c, that of RORC correlated negatively with HbA_1c. The expression pattern of RORA did not correlate with either of the two parameters. siRNA silencing of RORB or RORC in INS-1 (832/13) cells resulted in a significant downregulation of insulin mRNA expression and insulin secretion. These findings suggest that RORB and RORC are part of the molecular cascade that regulates insulin secretion in pancreatic β cells; and insight that provides for further work on the potential therapeutic utility of RORB and RORC genes in β cell dysfunction in type 2 diabetes.     

SENP5, a SUMO isopeptidase,induces apoptosis and cardiomyopathy

Cardiomyopathy presents a major health issue and is a leading cause of heart failure. Although a subset of familial cardiomyopathy is associated with genetic mutations, over 50% of cardiomyopathy is defined as idiopathic, the mechanisms underlying which are under intensive investigation. SUMO conjugation is a dynamic posttranslational modification that can be readily reversed by the activity of sentrin-specific proteases (SENPs). However, whether SENPs are implicated in heart disease pathophysiology remains unexplored. We observed a significant increase in the level of SENP5, a SUMO isopeptidase, in human idiopathic failing hearts. To reveal whether it plays a role in the pathogenesis of cardiac muscle disorders, we used a gain-of-function approach to overexpress SENP5 in murine cardiomyocytes (SENP5 transgenic, SENP5-Tg). Overexpression of SENP5 led to cardiac dysfunction, accompanied by decreased cardiomyocyte proliferation and elevated apoptosis. The increase in apoptosis preceded other detectable pathological changes, suggesting its causal link to cardiomyopathy. Further examination of SENP5-Tg hearts unveiled a decrease in SUMO attachment to dynamin related protein (Drp1), a factor critical for mitochondrial fission. Correspondingly, the mitochondria of SENP5-Tg hearts at an early developmental stage were significantly larger compared with those in the control hearts, suggesting that desumoylation of Drp1 at least partially accounts for the cardiac phenotypes observed in the SENP5-Tg mice. Finally, overexpression of Bcl2 in SENP5-Tg hearts improved cardiac function of SENP5-Tg mice, further supporting the notion that SENP5 mainly targets mitochondrial function in vivo. Our findings demonstrate an important role of the desumoylation enzyme SENP5 in the development of cardiac muscle disorders, and point to the SUMO conjugation pathway as a potential target in the prevention/treatment of cardiomyopathy. This article is part of a Special Issue entitled "Mitochondria: From Basic Mitochondrial Biology to Cardiovascular Disease".     

罗格列酮对内皮细胞单核细胞趋化蛋白-1和血管细胞黏附分子-1表达的影响

目的观察罗格列酮(RGZ)对高糖及C反应蛋白(CRP)诱导的人脐静脉内皮细胞(HUVECs)的单核细胞趋化蛋白-1(MCP-1)及血管细胞黏附分子-1(VCAM-1)mRNA和蛋白表达的影响。方法体外培养HUVECs,细胞传至5代,随机分为7组,正常对照组(C组),高糖组(HG组),高糖+CRP组(HGC组),CRP组,高糖+RGZ组(HGR组),高糖+CRP+RGZ组(HGCR组),CRP+RGZ组(CRPR组)。采用RGZ 5.0μmol/L干预HUVECs24 h,RT-PCR、Western blot法分别检测干预前后MCP-1、VCAM-1 mRNA和蛋白的表达水平。结果HG组、HGC组、CRP组HUVECs中MCP-1、VCAM-1的mRNA和蛋白水平较C组显著升高(P<0.01);RGZ干预后,HGR组、HGCR组、CRPR组分别较HG组、HGC组、CRP组MCP-1、VCAM-1的mRNA和蛋白水平显著降低(P<0.01)。结论RGZ通过降低HUVECs中MCP-1、VCAM-1的表达,延缓糖尿病动脉粥样硬化的进程。     

Dexamethasone and Cyclic AMP Regulate Sodium Phosphate Cotransporter (NaPi-IIb and Pit-1) mRNA and Phosphate Uptake in Rat Alveolar Type II Epithelial Cells

Alveolar epithelial type II (AT II) cells need phosphate (Pi) for surfactant synthesis. The Na-dependent (Na_d) Pi transporters NaPi-IIb and Pit-1 are expressed in lung, but their expression, regulation, and function in AT II cells remain unclear. We studied NaPi-IIb and Pit-1 mRNA expression in cultured AT II cells isolated from adult rat lung, their regulation by agents known to enhance surfactant production, dexamethasone (dex) and dibutyryl cyclic AMP (cAMP), and the effects of dex and cAMP on Na_d Pi uptake by this cell type. By Northern analysis, cultured AT II cells expressed both NaPi-IIb (4.8 and 4.0 kb) and Pit-1 (4.3 kb) mRNA. Treatment with 100 nmol/l dex for 24 h decreased the expression of both mRNAs (to 0.48 ± 0.06 and 0.77 ± 0.05, respectively, as compared to control), while 0.1 mmol/l cAMP stimulated NaPi-IIb (1.94 ± 0.22) but not Pit-1 mRNA (0.90 ± 0.05, compared to vehicle-treated cells). NaPi-IIb and Pit-1 proteins could not be identified by western analysis of plasma membrane preparations of cultured AT II cells. AT II cells take up Pi in a Na_d manner. Uptake was slightly (to 0.78-fold of the control) decreased by 100 nmol/l dex but not affected by 0.1 mmol/l cAMP treatment. Although NaPi-IIb mRNA expression was maintained to some extent by AT II cells kept in primary culture, Pi uptake was more closely related to Pit-1 mRNA expression.     

The nuclear receptor coactivator AIB3 is a modulator of HOMA beta-cell function in nondiabetic children

Objective The amplified in breast cancer‐3 protein (AIB3) is a nuclear coactivator involved in proliferation, apoptosis and development. AIB3 loss of function causes deficient insulin secretion in mice, indicating that AIB3 participates in β‐cell regulation. Our objective was to evaluate genetic variants located on AIB3 associated with β‐cell function in children and to analyse the effect of AIB3 overexpression on gene expression in insulin 1 (INS‐1) β‐pancreatic cells. Design Polymorphisms from AIB3 were genotyped in 148 children with normal or low birthweights for gestational age. The effect of AIB3 overexpression on gene expression was analysed by real‐time polymerase chain reaction (PCR) in INS‐1 cells. Results AIB3 variants were associated with homeostasis model assessment of β‐cell function (HOMA‐β‐cell) in children with normal or low birthweights for gestational age, but not with HOMA of insulin resistance (HOMA‐IR), or with birthweight. AIB3 overexpression increased the expression of genes involved in signalling, such as IRS‐1, IRS‐2, IGF‐II receptor or Foxo1, or of genes that control insulin secretion, such as Cplx2, Glut2 or Kv3·1 in INS‐1 cells. Conclusions Our results suggest that AIB3 contributes to the maintenance of β‐cell function in nondiabetic children and regulates gene expression in INS‐1 cells.