Mitochondrial Reversible Changes Determine Diastolic Function Adaptations During Myocardial (Reverse) Remodeling.

BACKGROUND: Often, pressure overload-induced myocardial remodeling does not undergo complete reverse remodeling after decreasing afterload. Recently, mitochondrial abnormalities and oxidative stress have been successively implicated in the pathogenesis of several chronic pressure overload cardiac diseases. Therefore, we aim to clarify the myocardial energetic dysregulation in (reverse) remodeling, mainly focusing on the mitochondria. METHODS: Thirty-five Wistar Han male rats randomly underwent sham or ascending (supravalvular) aortic banding procedure. Echocardiography revealed that banding induced concentric hypertrophy and diastolic dysfunction (early diastolic transmitral flow velocity to peak early-diastolic annular velocity ratio, E/E': sham, 13.6±2.1, banding, 18.5±4.1, P=0.014) accompanied by increased oxidative stress (dihydroethidium fluorescence: sham, 1.6×108±6.1×107, banding, 2.6×108±4.5×107, P<0.001) and augmented mitochondrial function. After 8 to 9 weeks, half of the banding animals underwent overload relief by an aortic debanding surgery (n=10). RESULTS: Two weeks later, hypertrophy decreased with the decline of oxidative stress (dihydroethidium fluorescence: banding, 2.6×108±4.5×107, debanding, 1.96×108±6.8×107, P<0.001) and diastolic dysfunction improved simultaneously (E/E': banding, 18.5±4.1, debanding, 15.1±1.8, P=0.029). The reduction of energetic demands imposed by overload relief allowed the mitochondria to reduce its activity and myocardial levels of phosphocreatine, phosphocreatine/ATP, and ATP/ADP to normalize in debanding towards sham values (phosphocreatine: sham, 38.4±7.4, debanding, 35.6±8.7, P=0.71; phosphocreatine/ATP: sham, 1.22±0.23 debanding, 1.11±0.24, P=0.59; ATP/ADP: sham, 6.2±0.9, debanding, 5.6±1.6, P=0.66). Despite the decreased mitochondrial area, complex III and V expression increased in debanding compared with sham or banding. Autophagy and mitophagy-related markers increased in banding and remained higher in debanding rats. CONCLUSIONS: During compensatory and maladaptive hypertrophy, mitochondria become more active. However, as the disease progresses, the myocardial energetic demands increase and the myocardium becomes energy deficient. During reverse remodeling, the concomitant attenuation of cardiac hypertrophy and oxidative stress allowed myocardial energetics, left ventricle hypertrophy, and diastolic dysfunction to recover. Autophagy and mitophagy are probably involved in the myocardial adaptation to overload and to unload. We conclude that these mitochondrial reversible changes underlie diastolic function adaptations during myocardial (reverse) remodeling.

Bearing My Heart: The Role of Extracellular Matrix on Cardiac Development, Homeostasis, and Injury Response.

The extracellular matrix (ECM) is an essential component of the heart that imparts fundamental cellular processes during organ development and homeostasis. Most cardiovascular diseases involve severe remodeling of the ECM, culminating in the formation of fibrotic tissue that is deleterious to organ function. Treatment schemes effective at managing fibrosis and promoting physiological ECM repair are not yet in reach. Of note, the composition of the cardiac ECM changes significantly in a short period after birth, concurrent with the loss of the regenerative capacity of the heart. This highlights the importance of understanding ECM composition and function headed for the development of more efficient therapies. In this review, we explore the impact of ECM alterations, throughout heart ontogeny and disease, on cardiac cells and debate available approaches to deeper insights on cell-ECM interactions, toward the design of new regenerative therapies.

Calcineurin is an important factor involved in glucose uptake in human adipocytes.

Calcineurin inhibitors are used in immunosuppressive therapy applied after transplantation, but they are associated with major metabolic side effects including the development of new onset diabetes. Previously, we have shown that the calcineurin inhibiting drugs tacrolimus and cyclosporin A reduce adipocyte and myocyte glucose uptakes by reducing the amount of glucose transporter type 4 (GLUT4) at the cell surface, due to an increased internalization rate. However, this happens without alteration in total protein and phosphorylation levels of key proteins involved in insulin signalling or in the total amount of GLUT4. The present study evaluates possible pathways involved in the altered internalization of GLUT4 and consequent reduction of glucose uptake provoked by calcineurin inhibitors in human subcutaneous adipose tissue. Short- and long-term treatments with tacrolimus, cyclosporin A or another CNI deltamethrin (herbicide) decreased basal and insulin-dependent glucose uptake in adipocytes, without any additive effects observed when added together. However, no tacrolimus effects were observed on glucose uptake when gene transcription and protein translation were inhibited. Investigation of genes potentially involved in GLUT4 trafficking showed only a small effect on ARHGEF11 gene expression (p < 0.05). In conlusion, the specific inhibition of calcineurin, but not that of protein phosphatases, decreases glucose uptake in human subcutaneous adipocytes, suggesting that calcineurin is an important regulator of glucose transport. This inhibitory effect is mediated via gene transcription or protein translation; however, expression of genes potentially involved in GLUT4 trafficking and endocytosis appears not to be involved in these effects.

Amyloid-beta disrupts calcium and redox homeostasis in brain endothelial cells.

In Alzheimer's disease, the accumulation of amyloid-beta (Aß) in the brain occurs in the parenchyma and cerebrovasculature. Several evidences support that the neuronal demise is potentiated by vascular alterations in the early stages of the disease, but the mechanisms responsible for the dysfunction of brain endothelial cells that underlie these cerebrovascular changes are unknown. Using rat brain microvascular endothelial cells, we found that short-term treatment with a toxic dose of Aß1-40 inhibits the Ca(2+) refill and retention ability of the endoplasmic reticulum and enhances the mitochondrial and cytosolic response to adenosine triphosphate (ATP)-stimulated endoplasmic reticulum Ca(2+) release. Upon prolonged Aß1-40 exposure, Ca(2+) homeostasis was restored concomitantly with a decrease in the levels of proteins involved in its regulation operating at the plasma membrane, endoplasmic reticulum, and mitochondria. Along with perturbations in Ca(2+) regulation, an early increase in the levels of oxidants and a decrease in the ratio between reduced and oxidized glutathione were observed in Aß1-40-treated endothelial cells. Under these conditions, the nuclear levels of oxidative stress-related transcription factors, namely, hypoxia-inducible factor 1α and nuclear factor (erythroid-derived 2)-related factor 2, were enhanced as well as the protein levels of target genes. In conclusion, Aß1-40 affects several mechanisms involved in Ca(2+) homeostasis and impairs the redox homeostasis simultaneously with stimulation of protective stress responses in brain endothelial cells. However, the imbalance between cell death and survival pathways leads to endothelial dysfunction that in turn contributes to cerebrovascular impairment in Alzheimer's disease.

Activation of the endoplasmic reticulum stress response by the amyloid-beta 1-40 peptide in brain endothelial cells.

Neurovascular dysfunction arising from endothelial cell damage is an early pathogenic event that contributes to the neurodegenerative process occurring in Alzheimer's disease (AD). Since the mechanisms underlying endothelial dysfunction are not fully elucidated, this study was aimed to explore the hypothesis that brain endothelial cell death is induced upon the sustained activation of the endoplasmic reticulum (ER) stress response by amyloid-beta (Aß) peptide, which deposits in the cerebral vessels in many AD patients and transgenic mice. Incubation of rat brain endothelial cells (RBE4 cell line) with Aß1-40 increased the levels of several markers of ER stress-induced unfolded protein response (UPR), in a time-dependent manner, and affected the Ca(2+) homeostasis due to the release of Ca(2+) from this intracellular store. Finally, Aß1-40 was shown to activate both mitochondria-dependent and -independent apoptotic cell death pathways. Enhanced release of cytochrome c from mitochondria and activation of the downstream caspase-9 were observed in cells treated with Aß1-40 concomitantly with caspase-12 activation. Furthermore, Aß1-40 activated the apoptosis effectors' caspase-3 and promoted the translocation of apoptosis-inducing factor (AIF) to the nucleus demonstrating the involvement of caspase-dependent and -independent mechanisms during Aß-induced endothelial cell death. In conclusion, our data demonstrate that ER stress plays a significant role in Aß1-40-induced apoptotic cell death in brain endothelial cells suggesting that ER stress-targeted therapeutic strategies might be useful in AD to counteract vascular defects and ultimately neurodegeneration.

Cholesterol and statins in Alzheimer's disease: current controversies.

Alzheimer's disease (AD) is the principal cause of dementia in older people, and accumulation of amyloid-beta (Abeta) peptide is a crucial event in AD pathogenesis. Despite opposite results found in literature, increased evidence posits that high cholesterol levels enhance the risk to develop AD. In fact, cholesterol metabolism and catabolism are affected in this neurodegenerative disorder. Since amyloid precursor protein (APP) processing and subsequent Abeta production are dependent on membrane cholesterol content and on levels of isoprenoid intermediates in the cholesterol biosynthesis pathway, changes in cholesterol might have different consequences on Abeta formation. These pieces of evidence support that inhibitors of cholesterol synthesis, like statins, could have a therapeutic role in AD. Many studies about the effect of statins use in AD show conflicting results; however, some authors explain it by the differences in administrated doses. Recent studies demonstrate that statins can efficiently decrease Abeta formation from APP and be neuroprotective against the peptide toxicity. Because of the high number of pleiotropic effects of statins, novel molecular mechanisms that account for the beneficial effect of these drugs on AD might be discovered in a near future.

Neuroprotective effects of statins in an in vitro model of Alzheimer's disease.

Statins, used as cholesterol-lowering drugs, were reported to reduce the progression of Alzheimer's disease (AD). However, the molecular mechanisms underlying these findings remain to be clarified and it is not well understood whether this beneficial effect is due to simply lowering cholesterol levels. This study was aimed to investigate the neuroprotective effect of simvastatin and lovastatin, lipophilic statins that can transverse the blood brain barrier, against the toxicity triggered by the AD-associated amyloid-beta (Abeta) peptides and to analyze if such protection is cholesterol-independent. Using primary cultures of cortical neurons treated with Abeta1-40 peptide, we have demonstrated that pre-incubation with statins prevents the rise in cytosolic Ca2+ concentration and the accumulation of reactive oxygen species induced by Abeta through mechanisms independent of cholesterol reduction. The neuroprotective actions of statins were rather attributable to their ability to reduce isoprenyl intermediates levels in the cholesterol biosynthetic pathway since their effect was reversed by geranyl pyrophosphate while cholesterol addition was ineffective. Consequently, statins were shown to rescue cortical neurons from Abeta-40-induced caspase-3-dependent apoptosis. Moreover, our results revealed that simvastatin, at neuroprotective concentrations against Abeta-induced toxicity, is not able to activate Akt or ERK2, two signaling kinases with neuroprotective roles against apoptosis.