GRK2 contributes to glucose mediated calcium responses and insulin secretion in pancreatic islet cells

Diabetes is a metabolic syndrome rooted in impaired insulin and/or glucagon secretory responses within the pancreatic islets of Langerhans (islets). Insulin secretion is primarily regulated by two key factors: glucose-mediated ATP production and G-protein coupled receptors (GPCRs) signaling. GPCR kinase 2 (GRK2), a key regulator of GPCRs, is reported to be downregulated in the pancreas of spontaneously obesogenic and diabetogenic mice (ob/ob). Moreover, recent studies have shown that GRK2 non-canonically localizes to the cardiac mitochondrion, where it can contribute to glucose metabolism. Thus, islet GRK2 may impact insulin secretion through either mechanism. Utilizing Min6 cells, a pancreatic ß-cell model, we knocked down GRK2 and measured glucose-mediated intracellular calcium responses and insulin secretion. Silencing of GRK2 attenuated calcium responses, which were rescued by pertussis toxin pre-treatment, suggesting a Gαi/o-dependent mechanism. Pancreatic deletion of GRK2 in mice resulted in glucose intolerance with diminished insulin secretion. These differences were due to diminished insulin release rather than decreased insulin content or gross differences in islet architecture. Furthermore, a high fat diet feeding regimen exacerbated the metabolic phenotype in this model. These results suggest a new role for pancreatic islet GRK2 in glucose-mediated insulin responses that is relevant to type 2 diabetes disease progression.

Environmental Regulation of the Heart: The Role of Non-Coding RNA and Epigenetics in Influencing Mitochondrial and Cellular Health

The mitochondrion, a small but ubiquitously distributed organelle in the cell, continues to be the focus of many disease pathogeneses, tissue and organ dysfunctions, and other morbidities that occur throughout the body. The purpose of this work was to understand how cardiac mitochondrion are altered in disease and pathological states, specifically in their adaptation to environmentally stimulated regulatory networks, such as epigenetic modifications and promotion/inhibition of non-coding RNAs. Acute stress to mitochondrial regulation (inhalation toxicology) as well as chronic (type 2 diabetes mellitus) was examined. Using a FVB transgenic microRNA-378a mouse knockout model, the cardiovascular impact derived from altering the innate microRNA-378a response following acute nano-TiO2 inhalation exposure was evaluated. In atrial tissue from 50 patients (30 non-diabetic and 20 type 2 diabetic) physiological, biochemical, genomic, and epigenomic factors were assessed using machine learning algorithms in an attempt to better predict the pathogenesis of the disease in the heart. Next-generation sequencing was performed on human patient and FVB mouse mitochondrial and cytoplasmic non-coding RNA populations, along with polynucleotide phosphorylase (PNPase) crosslinking immunoprecipitation (CLIP). Ultimately, the work summarized in the preceding experiments highlights how multiple pathological insults, whether chronic or acute, can influence the underlying molecular, regulatory networks in the heart. While overt cardiovascular and mitochondrial dysfunction follow insult, an emphasis on epigenetic control and non-coding RNA regulation may prove to be primary axes for therapeutic intervention. As we continue to pursue more informed and predictive assessments of cardiovascular dysfunction, the mitochondrion remains at the heart of the issue.

New Insights into Mechanisms of Cardioprotection Mediated by Thyroid Hormones

Heart failure represents the final common outcome in cardiovascular diseases. Despite significant therapeutic advances, morbidity and mortality of heart failure remain unacceptably high. Heart failure is preceded and sustained by a process of structural remodeling of the entire cardiac tissue architecture. Prevention or limitation of cardiac remodeling in the early stages of the process is a crucial step in order to ameliorate patient prognosis. Acquisition of novel pathophysiological mechanisms of cardiac remodeling is therefore required to develop more efficacious therapeutic strategies. Among all neuroendocrine systems, thyroid hormone seems to play a major homeostatic role in cardiovascular system. In these years, accumulating evidence shows that the “low triiodothyronine” syndrome is a strong prognostic, independent predictor of death in patients affected by both acute and chronic heart disease. In experimental models of cardiac hypertrophy or myocardial infarction, alterations in the thyroid hormone signaling, concerning cardiac mitochondrion, cardiac interstitium, and vasculature, have been suggested to be related to heart dysfunction. The aim of this brief paper is to highlight new developments in understanding the cardioprotective role of thyroid hormone in reverting regulatory networks involved in adverse cardiac remodeling. Furthermore, new recent advances on the role of specific miRNAs in thyroid hormone regulation at mitochondrion and interstitial level are also discussed.