P6309Impaired secretion of clusterin in pericardial fluid of diabetics, a deleterious outcome for the cardiac micro-vasculature

Background

Extracellular vesicles are vital mediators of cell-to-cell communications. We previously demonstrated that in the adult heart, exosomes released in the pericardial fluid (PF) have the functional capability to induce cell survival and angiogenesis in recipient endothelial cells. It has previously been shown that PF exosomes from patients with an existing myocardial infarction (MI) contain clusterin (CLU). Remarkably, secreted CLU is cardio-protective as evidenced by enhanced arteriogenesis and reduced apoptosis in animal models of MI. We hypothesize that type 2 Diabetes Mellitus (T2DM) along with ischemic heart disease (IHD) alters PF EV content impairing its reparative angiogenic potential.

Aim

To investigate the role of T2DM in modulating human PF exosomal content and its vascular action.

Methods and results

PF samples were collected from 3 different groups of patients (N=3): 1) Ischemic heart disease (IHD) with or 2) without T2DM, and 3) non-ischaemic, non-diabetic controls operated for mitral valve repair.

The impact of PF exosomes on human coronary microvascular ECs (HCMECs) was evaluated by cell based functional assays for measuring apoptosis, proliferation and angiogenesis. Interestingly, unlike PF exosomes from control patients, PF exosomes from DM patients with IHD promoted EC apoptosis and impaired angiogenesis.

To investigate the effect of T2DM on PF content, we performed high throughput proteomic and metabolomic analysis of whole PF and PF EVs. We identified proteins and metabolites that were differentially expressed under T2DM condition by using the R package Limma. Employing a network approach, protein and metabolic data were integrated by using our newly developed inhouse R package Metabosignal. This networks approach revealed an interesting interaction circuit involving protein CLU. The T2DM-associated reduction of CLU level in the PF, identified from the “omics” analyses was confirmed by ELISA (n=8 patients per group).

To examine the effects of DM and ischemia on CLU intracellular expression and secretion, HCMECs were exposed to high D-glucose (HG, 25 mM) and hypoxia (1%O2). In line with our PF data, HCMECs exposed to HG and hypoxia showed lower levels of both CLU mRNA and secreted CLU (ELISA). Importantly, recombinant CLU (rCLU) treatment on HCMECs rescued their angiogenic potential, induced cell proliferation and protected them from apoptosis under both HG and hypoxia conditions. In addition, silencing of endogenous levels of CLU in HCMECs impaired angiogenesis, suggesting that CLU might be an inherent component of the angiogenesis machinery in ECs.

Conclusions

This study suggests that DM reduces the level of secreted CLU in the PF, depriving myocardial micro-vessels of this protective and regenerative mediator. Restoring diminished CLU levels in the diabetic heart could be a possible therapeutic approach for contrasting diabetic micro-angiopathy.

Acknowledgement/Funding

British Heart Foundation Program Grant

Leptin signal transduction underlies the differential metabolic response of LEW and WKY rats to cafeteria diet

Although the effect of genetic background on obesity-related phenotypes is well established, the main objective of this study is to determine the phenotypic responses to cafeteria diet (CAF) of two genetically distinct inbred rat strains and give insight into the molecular mechanisms that might be underlying. Lewis (LEW) and Wistar-Kyoto (WKY) rats were fed with either a standard or a CAF diet. The effects of the diet and the strain in the body weight gain, food intake, respiratory quotient, biochemical parameters in plasma as well as in the expression of genes that regulate leptin signalling were determined. Whereas CAF diet promoted weight gain in LEW and WKY rats, as consequence of increased energy intake, metabolic management of this energy surplus was significantly affected by genetic background. LEW and WKY showed a different metabolic profile, LEW rats showed hyperglycaemia, hypertriglyceridemia and high FFA levels, ketogenesis, high adiposity index and inflammation, but WKY did not. Leptin signalling, and specifically the LepRb-mediated regulation of STAT3 activation and Socs3 gene expression in the hypothalamus were inversely modulated by the CAF diet in LEW (upregulated) and WKY rats (downregulated). In the present study, we show evidence of gene-environment interactions in obesity exerted by differential phenotypic responses to CAF diet between LEW and WKY rats. Specifically, we found the leptin-signalling pathway as a divergent point between the strain-specific adaptations to diet.

Gene copy number variation and common human disease

Variation in gene copy number is increasingly recognized as a common, heritable source of inter-individual differences in genomic sequence. The role of copy number variation is well established in the pathogenesis of rare genomic disorders. More recently, germline and somatic copy number variation have been shown to be important pathogenic factors in a range of common diseases, including infectious, autoimmune and neuropsychiatric diseases and cancer. In this review, we describe the range of methods available for measuring copy number variants (CNVs) in individuals and populations, including the limitations of presently available assays, and highlight some key examples of common diseases in which CNVs have been shown clearly to have a pathogenic role. Although there has been major progress in this field in the last 5 years, understanding the full contribution of CNVs to the genetic basis of common diseases will require further studies, with more accurate CNV assays and larger cohorts than have presently been completed.

Archival, demographic and genetic studies define a Sardinian sub-isolate as a suitable model for mapping complex traits

Genetic isolates represent exceptional resources for the mapping of complex traits but not all isolates are similar. We have selected a genetic and cultural isolate, the village of Talana from an isolated area of Sardinia, and propose that this population is suitable for the mapping of complex traits. A wealth of historical and archive data allowed the reconstruction of the demographic and genealogical history of the village. Key features of the population, which has grown slowly with no significant immigration, were defined by using a combination of historical, demographic and genetic studies. The genealogy of each Talana inhabitant was reconstructed and the main maternal and paternal lineages of the village were defined. Haplotype and phylogenetic analyses of the Y chromosome and characterisation of mitochondrial DNA haplogroups were used to determine the number of ancestral village founders. The extent of linkage disequilibrium (LD) was evaluated by the analysis of several microsatellites in chromosomal region Xq13.3, which was previously used to asses the extension of LD. Genealogical reconstructions were confirmed and reinforced by the genetic analyses, since some lineages were found to have merged prior to the beginning of the archival records, suggesting an even smaller number of founders than initially predicted. About 80% of the present-day population appears to derive from eight paternal and eleven maternal ancestral lineages. LD was found to span, on average, a 5-Mb region in Xq13.3. This suggests the possibility of identifying identical-by-descent regions associated with complex traits in a genome-wide search by using a low-density marker map. The present study emphasises the importance of combining genetic studies with genealogical and historical information.

Identification of a new candidate locus for uric acid nephrolithiasis

Renal stone formation is a common multifactorial disorder, of unknown etiology, with an established genetic contribution. Lifetime risk for nephrolithiasis is approximately 10% in Western populations, and uric acid stones account for 5%-10% of all stones, depending on climatic, dietary, and ethnic differences. We studied a small, isolated founder population in Sardinia, characterized by an increased prevalence of uric acid stones, and performed a genomewide search in a deep-rooted pedigree comprising many members who formed uric acid renal stones. The pedigree was created by tracing common ancestors of affected individuals through a genealogical database based on archival records kept by the parish church since 1640. This genealogical information was used as the basis for the study strategy, involving screening for alleles shared among affected individuals, originating from common ancestors, and utilization of large pedigrees to obtain greater power for linkage detection. We performed multistep linkage and allele-sharing analyses. In the initial stage, 382 markers were typed in 14 closely related affected subjects; interesting regions were subsequently investigated in the whole sample. We identified two chromosomal regions that may harbor loci with susceptibility genes for uric acid stones. The strongest evidence was observed on 10q21-q22, where a LOD score of 3.07 was obtained for D10S1652 under an affected-only dominant model, and a LOD score of 3.90 was obtained using a dominant pseudomarker assignment. The localization was supported also by multipoint allele-sharing statistics and by haplotype analysis of familial cases and of unrelated affected subjects collected from the isolate. In the second region on 20q13.1-13.3, multipoint nonparametric scores yielded suggestive evidence in a approximately 20-cM region, and further analysis is needed to confirm and fine-map this putative locus. Replication studies are required to investigate the involvement of these regions in the genetic contribution to uric acid stone formation.