Expression of the skeletal muscle dystrophin-dystroglycan complex and syntrophin-nitric oxide synthase complex is severely affected in the type 2 diabetic Goto-Kakizaki rat

The inability of insulin to stimulate glucose metabolism in skeletal muscle fibres is a classic characteristic of type 2 diabetes. Using the non-obese Goto-Kakizaki rat as an established animal model of this type of diabetes, sucrose gradient centrifugation studies were performed and confirmed the abnormal subcellular location of the glucose transporter GLUT4. In addition, this analysis revealed an unexpected drastic reduction in the surface membrane marker beta-dystroglycan, a dystrophin-associated glycoprotein. Based on this finding, a comprehensive immunoblotting survey was conducted which showed a dramatic decrease in the Dp427 isoform of dystrophin and the alpha/beta-dystroglycan subcomplex, but not in laminin, sarcoglycans, dystrobrevin, and excitation-contraction-relaxation cycle elements. Thus, the backbone of the trans-sarcolemmal linkage between the extracellular matrix and the actin membrane cytoskeleton might be structurally impaired in diabetic fibres. Immunohistochemical studies revealed that the reduction in the dystrophin-dystroglycan complex does not induce obvious signs of muscle pathology, and is neither universal in all fibres, nor fibre-type specific. Most importantly, the expression of alpha-syntrophin and the syntrophin-associated neuronal isoform of nitric oxide synthase, nNOS, was demonstrated to be severely reduced in diabetic fibres. The loss of the dystrophin-dystroglycan complex and the syntrophin-nNOS complex in selected fibres suggests a weakening of the sarcolemma, abnormal signalling and probably a decreased cytoprotective mechanism in diabetes. Impaired anchoring of the cortical actin cytoskeleton via dystrophin might interfere with the proper recruitment of the glucose transporter to the surface membrane, following stimulation by insulin or muscle contraction. This may, at least partially, be responsible for the insulin resistance in diabetic skeletal muscles.     

Cell type-specific activation of metabolism reveals that beta-cell secretion suppresses glucagon release from alpha-cells in rat pancreatic islets

Abnormal glucagon secretion is often associated with diabetes mellitus. However, the mechanisms by which nutrients modulate glucagon secretion remain poorly understood. Paracrine modulation by beta- or delta-cells is among the postulated mechanisms. Herein we present further evidence of the paracrine mechanism. First, to activate cellular metabolism and thus hormone secretion in response to specific secretagogues, we engineered insulinoma INS-1E cells using an adenovirus-mediated expression system. Expression of the Na+-dependent dicarboxylate transporter (NaDC)-1 resulted in 2.5- to 4.6-fold (P < 0.01) increases in insulin secretion in response to various tricarboxylic acid cycle intermediates. Similarly, expression of glycerol kinase (GlyK) increased insulin secretion 3.8- or 4.2-fold (P < 0.01) in response to glycerol or dihydroxyacetone, respectively. This cell engineering method was then modified, using the Cre-loxP switching system, to activate beta-cells and non-beta-cells separately in rat islets. NaDC-1 expression only in non-beta-cells, among which alpha-cells are predominant, caused an increase (by 1.8-fold, P < 0.05) in glucagon secretion in response to malate or succinate. However, the increase in glucagon release was prevented when NaDC-1 was expressed in whole islets, i.e., both beta-cells and non-beta-cells. Similarly, an increase in glucagon release with glycerol was observed when GlyK was expressed only in non-beta-cells but not when it was expressed in whole islets. Furthermore, dicarboxylates suppressed basal glucagon secretion by 30% (P < 0.05) when NaDC-1 was expressed only in beta-cells. These data demonstrate that glucagon secretion from rat alpha-cells depends on beta-cell activation and provide insights into the coordinated mechanisms underlying hormone secretion from pancreatic islets.     

Examining the potential for resource-dependent female reproductive fluid-sperm interactive effects in a livebearing fish

Sexually selected traits can be costly to produce and maintain. The amount of resources available to an individual is therefore expected to influence investment in costly sexual traits. While resource-dependent expression of sexually selected traits has traditionally been examined in males, resource limitation can also influence how sexual selection operates in females. Female reproductive fluids are thought to be costly to produce and may play an important role in shaping the outcome of postcopulatory sexual selection by influencing sperm performance. However, we know surprisingly little about whether and how female reproductive fluids are influenced by resource limitation. Here, we examine if resource restriction influences female reproductive fluid-sperm interactive effects in the pygmy halfbeak (Dermogenys collettei), a small internally fertilizing freshwater fish where females store sperm. After experimentally altering female diets (high vs. restricted diets), we compared how female reproductive fluids influence two key metrics of sperm quality: sperm viability and velocity. While female reproductive fluids enhanced sperm viability and velocity, we found no evidence that female diet influenced the interactive effect between female reproductive fluids and sperm viability or velocity. Our findings build on the growing evidence that female reproductive fluids influence sperm performance and call for further attention to be devoted to understanding how resource quantity and quality influence how female reproductive fluids affect sperm performance.     

Farming for bees: annual variation in pollinator populations across agricultural landscapes

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Androgen metabolism and JAK/STAT pathway genes and prostate cancer risk

Background: Prostate cancer (PC) is the most frequently diagnosed solid tumor in U.S. men. Genome-wide association studies (GWAS) have identified over 40 risk-associated single nucleotide polymorphisms (SNPs), including variants in androgen pathway genes (e.g., KLK3 and AR). Androgens are important in PC and genes involved in this pathway are therefore candidates for conferring susceptibility to PC. Methods: In this hypothesis-testing study, we evaluated PC risk in association with SNPs in 22 candidate genes involved in androgen metabolism or interactions with the androgen receptor (AR). A total of 187 SNPs were genotyped in 1458 cases and 1351 age-matched controls from a population-based study. PC risk was estimated using adjusted unconditional logistic regression and multinomial regression models. Results: Single SNP analyses showed evidence (p < 0.05) for associations with 14 SNPs in 9 genes: NKX3.1, HSD17B3, AKR1C3, SULT2A1, CYP17A1, KLK3, JAK2, NCOA4 and STAT3. The most significant result was observed for rs2253502 in HSD17B3 (odds ratio, OR = 0.57, 95% CI: 0.39–0.84). In addition, five SNPs in four genes (CYP17A1, HSD17B4, NCOA4, and SULT2A1) were associated with more aggressive disease (p < 0.01). Conclusions: Our results replicate previously reported associations for SNPs in CYP17A1, HSD17B3, ARK1C3, NKX3.1, NCOA4 and KLK3. In addition, novel associations were observed for SNPs in JAK2, HSD17B4, and SULT2A1. These results will require replication in larger studies.     

LEA Gene Introns: is the Intron of Dehydrin Genes a Characteristic of the Serine-Segment?

Dehydrins, which belong to group 2 LEA proteins, are a family of intrinsically unstructured plant proteins that accumulate during the late stages of embryogenesis and in response to abiotic stresses. We have previously reported that the OpsDHN1 gene, encoding an SK₃-type acidic dehydrin protein from Opuntia streptacantha, contains an intron inserted within the sequence encoding the S-motif. Herein, we present an in silico analysis of intron sequences in dehydrin genes from mono- and dicotyledonous plants that reveals a preference for insertion within the nucleotide sequence encoding the S-motif. Sequence comparison of ten Dhn genes from Arabidopsis thaliana and the orthologous genes in Arabidopsis lyrata revealed that introns maintain considerable sequence identity and conserve the insertion pattern. Furthermore, syntenic regions were identified among eight orthologous genes of A. thaliana and A. lyrata, showing that correlated gene arrangements are conserved between these Arabidopsis species. Our study shows that most SKn-type dehydrins contain one intron that is conserved in phase and location; this intron is linked to the nucleotide sequence that encodes the S-motif.     

Substitution in Amino Acid 70 of Hepatitis C Virus Core Protein Changes the Adipokine Profile via Toll-Like Receptor 2/4 Signaling

Background & Aims

It has been suggested that amino acid (aa) substitution at position 70 from arginine (70R) to glutamine (70Q) in the genotype 1b hepatitis C virus (HCV) core protein is associated with insulin resistance and worse prognosis. However, the precise mechanism is still unclear. The aim of this study was to investigate the impact of the substitution at position 70 in HCV core protein on adipokine production by murine and human adipocytes.

Methods

The influence of treatment with HCV core protein (70R or 70Q) on adipokine production by both 3T3-L1 and human adipocytes were examined with real-time PCR and enzyme-linked immunosorbent assay (ELISA), and triglyceride content was also analyzed. The effects of toll-like receptor (TLR)2/4 inhibition on IL-6 production by 3T3-L1 induced by HCV core protein were examined.

Results

IL-6 production was significantly increased and adiponectin production was reduced without a change in triglyceride content by treatment with 70Q compared to 70R core protein in both murine and human adipocytes. IL-6 induction of 3T3-L1 cells treated by 70Q HCV core protein was significantly inhibited with anti-TLR2 antibody by 42%, and by TLR4 inhibitor by 40%.

Conclusions

Our study suggests that extracellular HCV core protein with substitution at position 70 enhanced IL-6 production and reduced adiponectin production from visceral adipose tissue, which can cause insulin resistance, hepatic steatosis, and ultimately development of HCC.