Growth pattern switch of renal cells and expression of cell cycle related proteins at the early stage of diabetic nephropathy

Renal hypertrophy, partly due to cell proliferation and hypertrophy, has been found correlated to renal function deterioration in diabetes mellitus. We screened the up-regulated cell cycle related genes to investigate cell growth and the expression of cell cycle regulating proteins at the early stage of diabetic nephropathy using STZ-induced diabetic rats. Cyclin E, CDK(2) and P(27) were found significantly up-regulated in diabetic kidney. Increased cell proliferation in the kidney was seen at day 3, peaked at day 5, and returned to normal level at day 30. Cyclin E and CDK(2) expression also peeked at day 5 and P(27) activity peaked at day 14. These findings indicate that a hyperplastic growth period of renal cells is followed by a hypertrophic growth period at the early stage of diabetes. The growth pattern switch may be regulated by cell cycle regulating proteins, Cyclin E, CDK(2), and P(27).     

压力后负荷增高大鼠心肌肥厚向心力衰竭的转变

目的观察单纯腹主动脉缩窄造成的心肌肥厚能否转变成为心力衰竭。方法实验选用8周龄的Wistar大鼠,使用7-0号尼龙线对其肾上腹主动脉进行缩窄手术,造成后负荷性心肌肥厚模型(LVH,n=10),同时设置假手术组(Sham,n=10)和正常组(Con,n=10)作为对照。术后第20周和第38周使用超声多普勒和多导生理仪对大鼠血流动力学进行检测。解剖后取出心脏,计算心脏/体重比,并通过HE染色和天狼猩红染色观察心脏形态和纤维化程度。结果腹主动脉结扎后第20周,LVH组大鼠心室壁肥厚,舒张功能下降(E/Aratio:LVH组:1.0±0.25,Con组:1.6±0.12)。术后38周,左心室壁肥厚程度有所下降,但是心室腔扩大,心脏收缩和舒张功能明显下降(EF:LVH组:44.8±8.42,Con组:70.9±5.19;MaxdP/dt:LVH组:4916±1267.3,Con组:14225±932.1;MindP/dt:LVH组:-3246±1217.3,Con组:-12138±725.2)。腹主动脉缩窄术后的动物心脏重量明显增加(3.58±0.32vs.2.34±0.15),HE染色和天狼猩红染色显示LVH组大鼠在术后38周心脏纤维化明显。结论腹主动脉缩窄造成的后负荷增高动物模型首先出现向心性心肌肥厚,伴以舒张功能下降,进而收缩功能下降,发展为心力衰竭。     

Kidney growth,hypertrophy and the unifying mechanism of diabetic complications

Summary. Michael Brownlee has proposed a ‘Unifying Mechanism’ of hyperglycemia-induced damage in diabetes mellitus. At the crux of this hypothesis is the generation of reactive oxygen species (ROS), and their impact on glycolytic pathways. Diabetes is the leading cause of chronic kidney failure. In the early phase of diabetes, prior to establishment of proteinuria or fibrosis, comes kidney growth and hyperfiltration. This early growth phase consists of an early period of hyperplasia followed by hypertrophy. Hypertrophy also contributes to cellular oxidative stress, and may precede the ROS perturbation of glycolytic pathways described in the Brownlee proposal. This increase in growth promotes hyperfiltration, and along with the hypertrophic phenotype appears required for hyperglycemia-induced cell damage and the progression of downstream diabetic complications. Here we will evaluate this growth phenomenon in the context of diabetes mellitus.     

Null mutants of Drosophila B-type lamin Dm(0) show aberrant tissue differentiation rather than obvious nuclear shape distortion or specific defects during cell proliferation

To elucidate the function of metazoan B-type lamins during development, new null mutations of the Drosophila B-type lamin gene, lamDm(0), were analyzed in parallel with the misg(sz18) mutation, a lamDm(0) allele reported previously. Although in all these mutants, lamin Dm(0) protein was undetectable in neuroblasts and imaginal disc cells from the second instar larval stage onward, cells continued to proliferate. In contrast to the embryonic lethality of another Drosophila lamDm(0) allele, lam(PM15), reported previously, lethality did not occur until late pupal stages. Chromosomal structure and the overall nuclear shape remained normal even at these late pupal stages, although obviously abnormal nuclear pore complex distribution was observed concomitant with the loss of lamin Dm(0) protein. Compensating expression of lamin C was not induced in the absence of lamin Dm(0). Thus, no lamin-containing nuclear structures were found in proliferating larval neuroblasts. We did find that developmental abnormalities appeared in specific organs during the late pupal stage, preceding lethality. Surprisingly, coordinated size increase (hypertrophy) of the ventriculus was observed accompanied by cell division and muscle layer formation. Hypertrophy of the ventriculus correlated with a decrease in ecdysteroid hormone receptor B1 (EcRB1) protein, and furthermore could be suppressed by a heat-inducible EcRB1 transgene. In contrast, both gonadal and CNS tissues exhibited underdevelopment.     

MYBPC3 polymorphism is a modifier for expression of cardiac hypertrophy in patients with hypertrophic cardiomyopathy

Clinical phenotype of hypertrophic cardiomyopathy exhibits significant inter- and intra-familial heterogeneities. To test if MYBPC3 polymorphism could modify the expression of cardiac hypertrophy, 226 patients with hypertrophic cardiomyopathy and 226 age- and sex-matched controls were recruited according to the diagnostic criteria of WHO. Genotyping was completed by using PCR, restrictive enzyme digestion, and sequencing. Three polymorphisms of MYBPC3 were studied, only the GG genotype at 18443 in exon 30 associated with thicker left ventricular wall (25.2+/-5.9 mm) in patient group, not the AA and AG genotypes (19.0+/-5.0mm, P<0.001). After multiple regression analysis for adjustment of age and sex, the association remained. No difference was found in the genotype distribution between control and patients. Our results point out that GG genotype of MYBPC3 might be a genetic risk factor for the expression of cardiac hypertrophic phenotype in the patients with hypertrophic cardiomyopathy.     

Myodulin is a novel potential angiogenic factor in skeletal muscle

We examined the expression and function of a gene we previously cloned from its downregulation in a muscle atrophy model. The encoded protein was named myodulin because of sequence homologies with the cartilage-specific chondromodulin-I (ChM-I) protein, its restricted expression in skeletal muscle tissue, and its modulating properties on vascular endothelial cells described here. We investigated the expression of myodulin in muscle fibers and cultured muscle cells. Myodulin RNA messengers were found in muscle fibers and their tendon extensions. Overexpression of myodulin fused to a FLAG peptide showed evidence of a muscle cell surface protein. Myodulin functions were assessed from similarities with chondromodulin-I. Coculture experiments using C(2)C(12) mouse myoblasts or myotubes, which stably overexpress myodulin, with H5V mouse cardiac vascular endothelial cells revealed that myodulin had a very active role in the invasive action of endothelial cells, without any evidence of extracellular myodulin secretion. Our results suggest that myodulin may be a muscle angiogenic factor operating through direct cell-to-cell interactions. This role is consistent with the correlation between modulations in myodulin expression and modifications in muscle microvascularization associated with activity-dependent muscle mass variations.     

IGF-1 induces human myotube hypertrophy by increasing cell recruitment

Insulin-like growth factor-1 (IGF-1) has been shown in rodents (i) in vivo to induce muscle fiber hypertrophy and to prevent muscle mass decline with age and (ii) in vitro to enhance the proliferative life span of myoblasts and to induce myotube hypertrophy. In this study, performed on human primary cultures, we have shown that IGF-1 has very little effect on the proliferative life span of human myoblasts but does delay replicative senescence. IGF-1 also induces hypertrophy of human myotubes in vitro, as characterized by an increase in the mean number of nuclei per myotube, an increase in the fusion index, and an increase in myosin heavy chain (MyHC) content. In addition, muscle hypertrophy can be triggered in the absence of proliferation by recruiting more mononucleated cells. We propose that IGF-1-induced hypertrophy can involve the recruitment of reserve cells in human skeletal muscle.     

Regulation of Sodium-Calcium Exchanger Activity by Creatine Kinase under Energy-compromised Conditions

Na⁺/Ca²⁺ exchanger (NCX) is one of the major mechanisms for removing Ca²⁺ from the cytosol especially in cardiac myocytes and neurons, where their physiological activities are triggered by an influx of Ca²⁺. NCX contains a large intracellular loop (NCXIL) that is responsible for regulating NCX activity. Recent evidence has shown that proteins, including kinases and phosphatases, associate with NCX1IL to form a NCX1 macromolecular complex. To search for the molecules that interact with NCX1IL and regulate NCX1 activity, we used the yeast two-hybrid method to screen a human heart cDNA library and found that the C-terminal region of sarcomeric mitochondrial creatine kinase (sMiCK) interacted with NCX1IL. Moreover, both sMiCK and the muscle-type creatine kinase (CKM) coimmunoprecipitated with NCX1 using lysates of cardiacmyocytes and HEK293T cells that transiently expressed NCX1 and various creatine kinases. Both sMiCK and CKM were able to produce a recovery in the decreased NCX1 activity that was lost under energy-compromised conditions. This regulation is mediated through a putative PKC phosphorylation site of sMiCK and CKM. The autophosphorylation and the catalytic activity of sMiCK and CKM are not required for their regulation of NCX1 activity. Our results suggest a novel mechanism for the regulation of NCX1 activity.