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.

Isomers of conjugated linoleic acid induce insulin resistance through a mechanism involving activation of protein kinase Cε in liver cells.

Conjugated linoleic acid (CLA) constitutes a group of isomers derived from linoleic acid. Diverse studies have suggested that these unsaturated fatty acids have beneficial effects on human health. However, it has also been reported that their consumption can generate alterations in hepatic tissue. Thus, in the present study, we evaluated the effect of two of the major isomers of CLA, cis-9, trans-11-CLA and trans-10, cis-12-CLA, in the regulation of insulin signaling in a hepatic cell model, clone 9 (C9). We found that the two isomers decrease insulin-stimulated phosphorylation of the main proteins involved in insulin signaling, such as Akt at Ser473 and Thr308, the insulin receptor at Tyr1158, IRS-1 at Tyr632, and GSK-3 at Ser9/21. Protein expression, however, was unaffected. Interestingly, both isomers of CLA promoted phosphorylation and activation of PKCε. Inhibition of PKCε activity by a dominant-negative form or knockdown of endogenous PKCε prevented the adverse effects of CLA isomers on insulin-induced Akt phosphorylation. Additionally, we also found that both isomers of CLA increase phosphorylation of IRS-1 at Ser612, a mechanism that probably underlies the inhibition of IRS-1 signaling by PKCε. Using confocal microscopy, we found that both isomers of CLA induced lipid accumulation in C9 cells with the presence of spherical cytosolic vesicles, suggesting their identity as neutral lipid droplets. These findings indicate that cis-9, trans-11-CLA and trans-10, cis-12-CLA isomers could have a significant role in the development of insulin resistance in hepatic C9 cells through IRS-1 serine phosphorylation, PKCε activation, and hepatic lipid accumulation.

Bisphenol A alters oocyte maturation by prematurely closing gap junctions in the cumulus cell-oocyte complex.

In ovarian follicles, cumulus cells communicate with the oocyte through gap junction intercellular communication (GJIC), to nurture the oocyte and control its meiosis arrest and division. Bisphenol A (BPA) is a monomer found in polycarbonate-made containers that can induce functional alterations, including impaired oocyte meiotic division and reduced molecule transfer in GJIC. However, how BPA alters oocyte meiotic division is unclear. We investigated whether BPA effects on oocyte meiotic division were correlated with reduced transfer in GJIC. Cumulus cell-oocyte complexes (COCs) isolated from mouse preovulatory follicles were cultured with 0, 0.22, 2.2, 22, 220, and 2200 nM BPA for 2 h. An additional 16-h incubation with epidermal growth factor (EGF) was performed to promote the occurrence of meiotic resumption and progression to metaphase II. Without EGF stimulus, BPA treatment increased the percentage of oocytes undergoing meiotic resumption, decreased GJIC in the COCs, and did not modify GJIC gene (Cx43 and Cx37) and protein (CX43) expression. Following EGF stimulus, BPA increased the percentage of oocytes that remained at the anaphase and telophase stages, and decreased the percentage of oocytes reaching the metaphase II stage. Concomitantly, BPA reduced the expansion of cumulus cells. Carbenoxolone (a GJIC inhibitor) and 6-diazo-5-oxo-l-norleucine (a cumulus cell-expansion inhibitor) exerted effects on meiotic division similar to those exerted by BPA. These data suggest that BPA accelerates meiotic progression, leading to impaired prophase I-to-metaphase II transition, and that this adverse effect is correlated with reduced bidirectional communication in the COC.

Functional histamine H3 and adenosine A2A receptor heteromers in recombinant cells and rat striatum.

In the striatum, histamine H3 receptors (H3Rs) are co-expressed with adenosine A2A receptors (A2ARs) in the cortico-striatal glutamatergic afferents and the GABAergic medium-sized spiny neurons that originate the indirect pathway of the basal ganglia. This location allows H3Rs and A2ARs to regulate the striatal GABAergic and glutamatergic transmission. However, whether these receptors can physically interact has not yet been assessed. To test this hypothesis, a heteromer-selective in vitro assay was used to detect functional complementation between a chimeric A2AR302-Gαqi4 and wild-type H3Rs in transfected HEK-293T cells. H3R activation with the agonist RAMH resulted in Ca2+ mobilization (pEC50 7.31 ±â€¯0.23; maximal stimulation, Emax 449 ±â€¯25% of basal) indicative of receptor heterodimerization. Functional H3R-A2AR heteromers were confirmed by co-immunoprecipitation and observations of differential cAMP signaling when both receptors were co-expressed in the same cells. In membranes from rat striatal synaptosomes, H3R activation decreased A2AR affinity for the agonist CGS-21680 (pKi values 8.10 ±â€¯0.04 and 7.70 ±â€¯0.04). Moreover, H3Rs and A2ARs co-immunoprecipitated in protein extracts from striatal synaptosomes. These results support the existence of a H3R-A2AR heteromer with possible physiological implications for the modulation of the intra-striatal transmission.

[Molecular Mechanisms of Insulin Resistance: An Update]. / Mecanismos Moleculares de la Resistencia a la Insulina: Una Actualización.

The biological actions of insulin are initiated by activating its membrane receptor, which triggers multiple signaling pathways to mediate their biological actions. Due to the importance of metabolic regulation and promoting functions of cell growth and proliferation, insulin actions are highly regulated to promote proper metabolic functioning and energy balance. If these mechanisms are altered, this can lead to a condition known as insulin resistance, which is the consequence of a deficient insulin signaling caused by mutations or post-translational modifications of the receptor or effector molecules located downstream. Insulin resistance is one of the main characteristics of pathological manifestations associated with type 2 diabetes mellitus, one of the leading causes of death in Mexico and worldwide. In recent years, it has been found that conditions such as inflammation, endoplasmic reticulum stress, and mitochondrial dysfunction promote insulin resistance. The aim of this review is to elucidate the molecular aspects of insulin resistance and the mechanisms involved in regulating its effects, with particular emphasis on the role of inflammation, endoplasmic reticulum stress, and mitochondrial dysfunction.

El papel de los ácidos grasos libres en la resistencia a la insulina.

Free fatty acids are essential nutritional components and recent studies identified them as signaling molecules in various physiological processes. It has now been shown that high levels of free fatty acids, particularly saturated fatty acids, may be associated with insulin resistance in obese patients with type 2 diabetes mellitus. Insulin resistance is important in clinical since it is related to various diseases including type 2 diabetes mellitus, dyslipidemia, and abnormalities at cardiovascular level. Recent studies have proposed different molecular mechanisms by which these lipids may alter the signaling pathway of insulin. The purpose of this review is to highlight recent advances in the study of the effect of free fatty acids as modulators of insulin response.

Oxidative stress induced by P2X7 receptor stimulation in murine macrophages is mediated by c-Src/Pyk2 and ERK1/2.

BACKGROUND: Activation of ATP-gated P2X7 receptors (P2X7R) in macrophages leads to production of reactive oxygen species (ROS) by a mechanism that is partially characterized. Here we used J774 cells to identify the signaling cascade that couples ROS production to receptor stimulation. METHODS: J774 cells and mP2X7-transfected HEK293 cells were stimulated with Bz-ATP in the presence and absence of extracellular calcium. Protein inhibitors were used to evaluate the physiological role of various kinases in ROS production. In addition, phospho-antibodies against ERK1/2 and Pyk2 were used to determine activation of these two kinases. RESULTS: ROS generation in either J774 or HEK293 cells (expressing P2X7, NOX2, Rac1, p47phox and p67phox) was strictly dependent on calcium entry via P2X7R. Stimulation of P2X7R activated Pyk2 but not calmodulin. Inhibitors of MEK1/2 and c-Src abolished ERK1/2 activation and ROS production but inhibitors of PI3K and p38 MAPK had no effect on ROS generation. PKC inhibitors abolished ERK1/2 activation but barely reduced the amount of ROS produced by Bz-ATP. In agreement, the amount of ROS produced by PMA was about half of that produced by Bz-ATP. CONCLUSIONS: Purinergic stimulation resulted in calcium entry via P2X7R and subsequent activation of the PKC/c-Src/Pyk2/ERK1/2 pathway to produce ROS. This signaling mechanism did not require PI3K, p38 MAPK or calmodulin. GENERAL SIGNIFICANCE: ROS is generated in order to kill invading pathogens, thus elucidating the mechanism of ROS production in macrophages and other immune cells allow us to understand how our body copes with microbial infections.

Evidence of an intracellular angiotensin-generating system and non-AT1, non-AT2 binding site in a human pancreatic cell line.

OBJECTIVES: To assess the presence of a local angiotensin-generating systems (LAGS) and its participation in tumor growth in the human pancreatic cancer derived cell line Capan-1. METHODS: Capan-1 cells were cultured in Dulbecco modified Eagle medium, and angiotensin I was assayed by radioimmunoassay and angiotensin II and vascular endothelial growth factor were assayed by enzyme-linked immunosorbent assay in the supernatant. Immunohistochemistry and reverse transcription-polymerase chain reaction were performed for the expression of AT1 and AT2 receptors. Angiotensin II binding assays and blockade were studied. RESULTS: High levels of both angiotensins I and II were found in Capan-1 cells, although neither angiotensin I nor angiotensin II was detected in the cell culture supernatant. Reverse transcription-polymerase chain reaction and immunocytochemistry revealed that Capan-1 cells do not express AT1 and AT2 receptors; however, specific binding to the cell membrane was identified for angiotensin II. Neither exogenous angiotensin II nor Dup753 (specific AT1 receptor blocker) affected Capan-1 cells' proliferation or vascular endothelial growth factor secretion. CONCLUSIONS: Detection of both angiotensin I and angiotensin II along with specific binding of angiotensin II in Capan-1 cells provides evidence of the existence of a LAGS that operates in an intracrine manner. Intracellular angiotensin II may play a role in the aggressiveness of pancreatic cancer and is a possible target for therapeutic agents.