AT1 receptor downregulation: A mechanism for improving glucose homeostasis.

There is a pathophysiological correlation between arterial hypertension and diabetes mellitus, established since the pre-diabetic state in the entity known as insulin resistance. It is known that high concentrations of angiotensin-II enable chronic activation of the AT1 receptor, promoting sustained vasoconstriction and the consequent development of high blood pressure. Furthermore, the chronic activation of the AT1 receptor has been associated with the development of insulin resistance. From a molecular outlook, the AT1 receptor signaling pathway can activate the JNK kinase. Once activated, this kinase can block the insulin signaling pathway, favoring the resistance to this hormone. In accordance with the previously mentioned mechanisms, the negative regulation of the AT1 receptor could have beneficial effects in treating metabolic syndrome and type 2 diabetes mellitus. This review explains the clinical correlation of the metabolic response that diabetic patients present when receiving negatively regulatory drugs of the AT1 receptor.

Palmitic acid decreases cell migration by increasing RGS2 expression and decreasing SERCA expression.

Palmitic acid, the main saturated fatty acid, is related with a wide range of metabolic disorders such as obesity, type 2 diabetes and heart disease. It is known that palmitic acid disturbs the expression of some important proteins for cell homeostasis such as SERCA and RGS2, however, the role of this lipid at the molecular level in these disorders is not completely elucidated. Thus, our aim was to determinate the effect of palmitic acid in a relevant cell process as it is cell migration and the participation of SERCA and RGS2 in this response. We found that palmitic acid reduces cell migration (determined by the Boyden chamber method) in an epithelial cell line (HEK293) and this effect is modulated by SERCA and RGS2 differential protein expression (measured by western blot). Also, overexpression of individual proteins, RGS2 and SERCA, produced a decrease and an increase on cell migration, respectively. Taken together, these data suggest that the expression of regulatory proteins is affected by high concentrations of saturated fatty acids and in consequence cell migration is diminished in epithelial cells.

TRPV4 activity regulates nuclear Ca2+ and transcriptional functions of ß-catenin in a renal epithelial cell model.

TRPV4 is a nonselective cationic channel responsive to several physical and chemical stimuli. Defects in TRPV4 channel function result in human diseases, such as skeletal dysplasias, arthropathies, and peripheral neuropathies. Nonetheless, little is known about the role of TRPV4 in other cellular functions, such as nuclear Ca2+ homeostasis or Ca2+ -regulated transcription. Here, we confirmed the presence of the full-length TRPV4 channel in the nuclei of nonpolarized Madin-Darby canine kidney cells. Confocal Ca2+ imaging showed that activation of the channel increases cytoplasmic and nuclear Ca2+ leading to translocation of TRPV4 out of the nucleus together with ß-catenin, a transcriptional regulator in the Wnt signaling pathway fundamental in embryogenesis, organogenesis, and cellular homeostasis. TRPV4 inhibits ß-catenin transcriptional activity through a direct interaction dependent upon channel activity. This interaction also occurs in undifferentiated osteoblastoma and neuroblastoma cell models. Our results suggest a mechanism in which TRPV4 may regulate differentiation in several cellular contexts.

Autonomous activation of CaMKII exacerbates diastolic calcium leak during beta-adrenergic stimulation in cardiomyocytes of metabolic syndrome rats.

Autonomous Ca2+/calmodulin-dependent protein kinase II (CaMKII) activation induces abnormal diastolic Ca2+ leak, which leads to triggered arrhythmias in a wide range of cardiovascular diseases, including diabetic cardiomyopathy. In hyperglycemia, Ca2+ handling alterations can be aggravated under stress conditions via the ß-adrenergic signaling pathway, which also involves CaMKII activation. However, little is known about intracellular Ca2+ handling disturbances under ß-adrenergic stimulation in cardiomyocytes of the prediabetic metabolic syndrome (MetS) model with obesity, and the participation of CaMKII in these alterations. MetS was induced in male Wistar rats by administering 30 % sucrose in drinking water for 16 weeks. Fluo 3-loaded MetS cardiomyocytes exhibited augmented diastolic Ca2+ leak (in the form of spontaneous Ca2+ waves) under basal conditions and that Ca2+ leakage was exacerbated by isoproterenol (ISO, 100 nM). At the molecular level, [3H]-ryanodine binding and basal phosphorylation of cardiac ryanodine receptor (RyR2) at Ser2814, a CaMKII site, were increased in heart homogenates of MetS rats with no changes in RyR2 expression. These alterations were not further augmented by Isoproterenol. SERCA pump activity was augmented 48 % in MetS hearts before ß-adrenergic stimuli, which is associated to augmented PLN phosphorylation at T17, a target of CaMKII. In MetS hearts. CaMKII auto-phosphorylation (T287) was increased by 80 %. The augmented diastolic Ca2+ leak was prevented by CaMKII inhibition with AIP. In conclusion, CaMKII autonomous activation in cardiomyocytes of MetS rats with central obesity significantly contributes to abnormal diastolic Ca2+ leak, increasing the propensity for ß-adrenergic receptor-driven lethal arrhythmias.

Inverse correlation between levels of glycated haemoglobin and expression levels of SERCA protein in Mexican patients with type 2 diabetes mellitus.

We examined the association between sarco/endoplasmic reticulum calcium ATPase (SERCA) expression and glycated hemoglobin (HbA1c) levels since alterations in this protein expression are associated with the genesis of insulin resistance. HbA1c levels and SERCA protein expression from platelets of Mexican patients diagnosed with type 2 diabetes mellitus (T2DM) were analyzed showing lower values of SERCA expression against the normal values we find in healthy people. Interestingly, as diabetes condition got worse; SERCA protein expression decreased gradually until it was undetectable. The results showed an inverse correlation between HbA1c and SERCA protein expression in T2DM patients. .

Enhanced Klotho availability protects against cardiac dysfunction induced by uraemic cardiomyopathy by regulating Ca2+ handling.

BACKGROUND AND PURPOSE: Klotho is a membrane-bound or soluble protein, originally identified as an age-suppressing factor and regulator of mineral metabolism. Klotho deficiency is associated with the development of renal disease, but its role in cardiac function in the context of uraemic cardiomyopathy is unknown. EXPERIMENTAL APPROACH: We explored the effects of Klotho on cardiac Ca2+ cycling. We analysed Ca2+ handling in adult cardiomyocytes from Klotho-deficient (kl/kl) mice and from a murine model of 5/6 nephrectomy (Nfx). We also studied the effect of exogenous Klotho supplementation, by chronic recombinant Klotho treatment, or endogenous Klotho overexpression, using transgenic mice overexpressing Klotho (Tg-Kl), on uraemic cardiomyopathy. Hearts from Nfx mice were used to study Ca2+ sensitivity of ryanodine receptors and their phosphorylation state. KEY RESULTS: Cardiomyocytes from kl/kl mice showed decreased amplitude of intracellular Ca2+ transients and cellular shortening together with an increase in pro-arrhythmic Ca2+ events compared with cells from wild-type mice. Cardiomyocytes from Nfx mice exhibited the same impairment in Ca2+ cycling as kl/kl mice. Changes in Nfx cardiomyocytes were explained by higher sensitivity of ryanodine receptors to Ca2+ and their increased phosphorylation at the calmodulin kinase type II and protein kinase A sites. Ca2+ mishandling in Nfx-treated mice was fully prevented by chronic recombinant Klotho administration or transgenic Klotho overexpression. CONCLUSIONS AND IMPLICATIONS: Klotho emerges as an attractive therapeutic tool to improve cardiac Ca2+ mishandling observed in uraemic cardiomyopathy. Strategies that improve Klotho availability are good candidates to protect the heart from functional cardiac alterations in renal disease.

Metabolic syndrome diminishes insulin-induced Akt activation and causes a redistribution of Akt-interacting proteins in cardiomyocytes.

Metabolic syndrome (MetS) is a cluster of cardiometabolic risk factors, with insulin resistance as a critical component for its development. Insulin signaling in the heart leads to Akt (also known as PKB) activation, a serine/threonine protein kinase, which regulates cardiac glucose metabolism and growth. Cardiac metabolic inflexibility, characterized by impaired insulin-induced glucose uptake and oxidation, has been reported as an early and consistent change in the heart of different models of MetS and diabetes; however, the evaluation of Akt activation has yielded variable results. Here we report in cardiomyocytes of MetS rats, diminished insulin-induced glucose uptake and Akt activation, evaluated by its impaired mobilization towards the plasma membrane and phosphorylation, and reflected in a re-distribution of its interacting proteins, assessed by label-free mass spectrometry (data are available via ProteomeXchange with identifier PXD013260). We report 45 proteins with diminished abundance in Akt complex of MetS cardiomyocytes, mainly represented by energy metabolism-related proteins, and also, 31 Akt-interacting proteins with increased abundance, which were mainly related to contraction, endoplasmic reticulum stress, and Akt negative regulation. These results emphasize the relevance of Akt in the regulation of energy metabolism in the heart and highlight Akt-interacting proteins that could be involved in the detrimental effects of MetS in the heart.

Impaired Activity of Ryanodine Receptors Contributes to Calcium Mishandling in Cardiomyocytes of Metabolic Syndrome Rats.

Metabolic syndrome (MetS) has become a global epidemic. MetS is a serious health problem because of its related cardiovascular complications, which include hypertension and delayed heart rate recovery after exercise. The molecular bases of cardiac dysfunction in MetS are still under scrutiny and may be related to anomalies in the activity and expression of key proteins involved in the cardiac excitation-contraction coupling (ECC). The cardiac Ca2+ channel/ryanodine receptor (RyR2) participates in releasing Ca2+ from internal stores and plays a key role in the modulation of ECC. We examined alterations in expression, phosphorylation status, Ca2+ sensitivity, and in situ function (by measuring Ca2+ sparks and Ca2+ transients) of RyR2; alterations in these characteristics could help to explain the Ca2+ handling disturbances in MetS cardiomyocytes. MetS was induced in rats by adding commercially refined sugar (30% sucrose) to their drinking water for 24 weeks. Cardiomyocytes of MetS rats displayed decreased Ca2+ transient amplitude and cell contractility at all stimulation frequencies. Quiescent MetS cardiomyocytes showed a decrease in Ca2+ spark frequency, amplitude, and spark-mediated Ca2+ leak. The [3H]-ryanodine binding data showed that functionally active RyRs are significantly diminished in MetS heart microsomes; and exhibited rapid Ca2+-induced inactivation. The phosphorylation of corresponding Ser2814 (a preferential target for CaMKII) of the hRyR2 was significantly diminished. RyR2 protein expression and Ser2808 phosphorylation level were both unchanged. Further, we demonstrated that cardiomyocyte Ca2+ mishandling was associated with reduced SERCA pump activity due to decreased Thr17-PLN phosphorylation, suggesting a downregulation of CaMKII in MetS hearts, though the SR Ca2+ load remained unchanged. The reduction in the phosphorylation level of RyR2 at Ser2814 decreases RyR2 availability for activation during ECC. In conclusion, the impaired in situ activity of RyR2 may also account for the poor overall cardiac outcome reported in MetS patients; hence, the SERCA pump and RyR2 are both attractive potential targets for future therapies.

Palmitic acid but not palmitoleic acid induces insulin resistance in a human endothelial cell line by decreasing SERCA pump expression.

Palmitic acid is a negative regulator of insulin activity. At the molecular level, palmitic acid reduces insulin stimulated Akt Ser473 phosphorylation. Interestingly, we have found that incubation with palmitic acid of human umbilical vein endothelial cells induced a biphasic effect, an initial transient elevation followed by a sustained reduction of SERCA pump protein levels. However, palmitic acid produced a sustained inhibition of SERCA pump ATPase activity. Insulin resistance state appeared before there was a significant reduction of SERCA2 expression. The mechanism by which palmitic acid impairs insulin signaling may involve endoplasmic reticulum stress, because this fatty acid induced activation of both PERK, an ER stress marker, and JNK, a kinase associated with insulin resistance. None of these effects were observed by incubating HUVEC-CS cells with palmitoleic acid. Importantly, SERCA2 overexpression decreased the palmitic acid-induced insulin resistance state. All these results suggest that SERCA pump might be the target of palmitic acid to induce the insulin resistance state in a human vascular endothelial cell line. Importantly, these data suggest that HUVEC-CS cells respond to palmitic acid-exposure with a compensatory overexpression of SERCA pump within the first hour, which eventually fades out and insulin resistance prevails.