Possible Involvement of HSP90-HSF1 Multichaperone Complex in Impairment of HSP72 Induction in the Failing Heart Following Myocardial Infarction in Rats

RIPK1 inhibition contributes to lysosomal membrane stabilization in ischemic astrocytes via a lysosomal Hsp70.1B-dependent mechanism

Receptor-interacting protein kinase 1 (RIPK1) contributes to necroptosis. Our previous study showed that pharmacological or genetic inhibition of RIPK1 protects against ischemic stroke-induced astrocyte injury. In this study, we investigated the molecular mechanisms underlying RIPK1-mediated astrocyte injury in vitro and in vivo. Primary cultured astrocytes were transfected with lentiviruses and then subjected to oxygen and glucose deprivation (OGD). In a rat model of permanent middle cerebral artery occlusion (pMCAO), lentiviruses carrying shRNA targeting RIPK1 or shRNA targeting heat shock protein 70.1B (Hsp70.1B) were injected into the lateral ventricles 5 days before pMCAO was established. We showed that RIPK1 knockdown protected against OGD-induced astrocyte damage, blocked the OGD-mediated increase in lysosomal membrane permeability in astrocytes, and inhibited the pMCAO-induced increase in astrocyte lysosome numbers in the ischemic cerebral cortex; these results suggested that RIPK1 contributed to the lysosomal injury in ischemic astrocytes. We revealed that RIPK1 knockdown upregulated the protein levels of Hsp70.1B and increased the colocalization of Lamp1 and Hsp70.1B in ischemic astrocytes. Hsp70.1B knockdown exacerbated pMCAO-induced brain injury, decreased lysosomal membrane integrity and blocked the protective effects of the RIPK1-specific inhibitor necrostatin-1 on lysosomal membranes. On the other hand, RIPK1 knockdown further exacerbated the pMCAO- or OGD-induced decreases in the levels of Hsp90 and the binding of Hsp90 to heat shock transcription factor-1 (Hsf1) in the cytoplasm, and RIPK1 knockdown promoted the nuclear translocation of Hsf1 in ischemic astrocytes, resulting in increased Hsp70.1B mRNA expression. These results suggest that inhibition of RIPK1 protects ischemic astrocytes by stabilizing lysosomal membranes via the upregulation of lysosomal Hsp70.1B; the mechanism underlying these effects involves decreased Hsp90 protein levels, increased Hsf1 nuclear translocation and increased Hsp70.1B mRNA expression.

Traditional Chinese Medicine Targeting Heat Shock Proteins as Therapeutic Strategy for Heart Failure

Heart failure (HF) is the terminal stage of multifarious heart diseases and is responsible for high hospitalization rates and mortality. Pathophysiological mechanisms of HF include cardiac hypertrophy, remodeling and fibrosis resulting from cell death, inflammation and oxidative stress. Heat shock proteins (HSPs) can ameliorate folding of proteins, maintain protein structure and stability upon stress, protect the heart from cardiac dysfunction and ameliorate apoptosis. Traditional Chinese medicine (TCM) regulates expression of HSPs and has beneficial therapeutic effect in HF. In this review, we summarized the function of HSPs in HF and the role of TCM in regulating expression of HSPs. Studying the regulation of HSPs by TCM will provide novel ideas for the study of the mechanism and treatment of HF.

Pioglitazone restores phosphorylation of downregulated caveolin-1 in right ventricle of monocrotaline-induced pulmonary hypertension

BACKGROUND

Caveolin-1 (cav-1) plays a role in pulmonary arterial hypertension (PAH). Monocrotaline (MCT)-induced PAH is characterized by a loss of cav-1 in pulmonary arteries; however, less is known regarding its role in the hypertrophied right ventricle (RV). We aimed to characterize the role of cav-1 and Hsp90 in the RV of MCT-induced PAH and their impact on endothelial nitric oxide synthase (eNOS). Additionally, we focused on restoration of cav-1 expression with pioglitazone administration.

METHODS

Male 12-week-old Wistar rats were injected subcutaneously with monocrotaline (60 mg/kg). Selected proteins (cav-1, eNOS, pSer1177eNOS, Hsp90) and mRNAs (cav-1α, cav-1β, eNOS) were determined in the RV and left ventricle (LV) 4 weeks later. In a separate MCT-induced PAH study, pioglitazone (10 mg/kg/d, orally) administration started on day 14 after MCT.

RESULTS

MCT induced RV hypertrophy and lung enlargement. Cav-1 and pTyr14cav-1 were decreased in RV. Caveolin-1α (cav-1α) and caveolin-1β (cav-1β) mRNAs were decreased in both ventricles. Hsp90 protein was increased in RV. eNOS and pSer1177eNOS proteins were unchanged in the ventricles. eNOS mRNA was reduced in RV. Pioglitazone treatment increased oxygen saturation and pTyr14cav-1 vs. MCT group.

CONCLUSIONS

Restoration of pTyr14cav-1 did not lead to amelioration of the disease, nor did it prevent RV hypertrophy and fibrosis, which was indicated by an increase in Acta2, Nppb, Col3a1, and Tgfβ1 mRNA.

Effects of 17-AAG on the RIP1/RIP3/MLKL pathway during the development of heart failure following myocardial infarction in rats

In a previous study, we suggested that the Hsp90 inhibitor 17-AAG prevents cardiac dysfunction in the failing heart following myocardial infarction in rats. Although it is assumed that the RIP1/RIP3/MLKL necroptotic pathway, which comprises client proteins for Hsp90, is involved; however, the relationship between the cardioprotective effects of 17-AAG and the activity of the cardiac RIP1/RIP3/MLKL necrosome-associated proteins in the failing heart following myocardial infarction remained unclear. Therefore, the levels of phosphorylated MLKL after myocardial infarction with or without Hsp90 inhibitor treatment were measured. Myocardial infarction was induced by ligation of the coronary artery (CAL) in Wistar rats. 17-AAG was injected from the 2nd to the 8th week after myocardial infarction. The administration of 17-AAG attenuated the cardiac dysfunction, hypertrophy, and fibrosis at the 8th week after CAL, simultaneously lessening the increases in the expression and phosphorylation levels of RIP1, RIP3, and MLKL in the area of the left ventricular muscle without infarct. These results indicate that the activation of the RIP1/RIP3/MLKL pathway is a common event in the development of chronic heart failure. Furthermore, our findings suggest that the effects of 17-AAG treatment on the improvement of cardiac function in rats after myocardial infarction is related to the attenuation of this RIP1/RIP3/MLKL pathway.

Hsp90 Inhibitor Attenuates the Development of Pathophysiological Cardiac Fibrosis in Mouse Hypertrophy via Suppression of the Calcineurin-NFAT and c-Raf-Erk Pathways

ABSTRACT

In the previous study, we showed that an Hsp90 inhibitor, 17-(allylamino)-17-demethoxygeldanamycin (17-AAG), attenuates hypertrophic remodeling of cardiomyocytes during the development of heart failure. In this present study, we investigated the effects of 17-AAG on cardiac fibrosis during the development of heart failure. We used pressure-loaded cardiac hypertrophic mice prepared by constriction of the transverse aorta (TAC), which induces significant cardiac fibrosis without scar tissue. From the sixth week after the TAC operation, vehicle or 17-AAG was administered intraperitoneally twice a week. Eight weeks after the operation, the vehicle-treated animals showed chronic heart failure. On the other hand, cardiac deterioration of the 17-AAG-treated animals was attenuated. In 17-AAG-treated animals, when the degree of fibrosis was observed by histological staining, their volume of fibrosis was found to be reduced. The content of calcineurin, an Hsp90 client protein, and the level of dephosphorylated NFATc2, a transcription factor in the cardiac fibroblasts, in the TAC mice was reduced by treatment with 17-AAG. Furthermore, c-Raf and Erk signaling, indicators for cell proliferation and collagen synthesis, was also attenuated. In in vitro experiments, the proliferation and collagen synthesis of the cultured cardiac fibroblasts were attenuated by the presence of 17-AAG. When cardiac fibroblasts were incubated with angiotensin II, calcineurin-NFATc2 and c-Raf-Erk signaling in the cells were activated. These activations were attenuated by 17-AAG. Our findings suggest that suppression of the calcineurin-NFAT and c-Raf-Erk pathways may partially contribute to the attenuation of myocardial fibrosis caused by treatment with 17-AAG. Therefore, our data imply that the Hsp90 inhibitor may have potential for novel therapeutic strategy for the treatment of heart failure.

Effects of Hsp90 inhibitor on the RIP1-RIP3-MLKL pathway during the development of heart failure in mice

Necroptosis is a programmed form of necrotic cell death. Necroptosis is regulated by the necroptosis-regulating proteins including receptor-interacting protein (RIP) 1, RIP3, and mixed lineage kinase domain-like (MLKL), the activities of which are modulated by the molecular chaperone heat-shock protein (Hsp) 90. Presently, to clarify the relationship between Hsp90 and necroptotic pathway proteins, RIP1, RIP3, and MLKL in the development of heart failure, we examined the effects of Hsp90 inhibitor treatment on the RIP1-RIP3-MLKL pathway in mice following transverse aortic constriction (TAC). In this study, TAC mice showed typical signs of heart failure at the 8th week after the operation. In the failing heart, the levels of these regulatory proteins and those of their phosphorylated forms were increased, suggesting that necroptosis contributed to the development of heart failure in the TAC mice. The increases in RIP1, RIP3, and MLKL after TAC were reversed by the administration of an Hsp90 inhibitor. Furthermore, the rise in the phosphorylation levels of these 3 proteins were attenuated by the Hsp90 inhibitor. Concomitantly, cardiac functions were preserved. We also found that exposure of cultured adult mouse cardiomyocytes to the Hsp90 inhibitor attenuated necrotic cell death induced by tumor necrosis factor-α via suppression of RIP1, RIP3, and MLKL activation in in vitro experiments. Taken together, our findings suggest that inhibition of Hsp90 should have therapeutic effects by reducing the activation of RIP1-RIP3-MLKL pathway in the hypertrophied heart and thus could be a new therapeutic strategy for chronic heart failure.

Transplantation of cardiac Sca-1-positive cells rather than c-Kit-positive cells preserves mitochondrial oxygen consumption of the viable myocardium following myocardial infarction in rats

The cardiosphere-derived cell (CDC) is one of the candidate cells used for cardiac regenerative therapy. Cardiospheres are mixture of cells including c-Kit⁺ cells, stem cell antigen (Sca)-1⁺ cells, and other types of cardiac progenitor cells. In this study, we compared the effect of transplantation of isolated Sca-1⁺ cells and c-Kit⁺ cells with that of the crude CDCs (CrCDCs). Focusing on the differences in the ability for secretion of paracrine factors among 3 types of cells, we determined the effects of transplantation of these cells on cardiac intracellular signaling and mitochondrial function in rats with permanently ligated coronary arteries. We showed that the transplantation of these cells resulted in a preservation of the cardiac pump function and mitochondrial respiration at the 8th week after myocardial infarction. However, mitochondrial function in the c-Kit⁺ cell-transplanted group was lower than that in the other 2 groups. Furthermore, we found that activation levels of intracellular signaling proteins after cell transplantation may have been due to the ability of secretion of growth factors by these transplanted cell types. Our findings indicate the possibility that CrCDC and Sca-1⁺ cells rather than c-Kit⁺ cells may be used therapeutically to preserve cardiac function and energy metabolism after myocardial infarction.

Heat-shock protein 90 modulates cardiac ventricular hypertrophy via activation of MAPK pathway

The Raf/MAPK/ERK kinase (Mek)/extracellular signal-regulated kinases (Erk) pathway is activated in cardiac hypertrophy after a myocardial infarction. Although heat-shock protein 90 (Hsp90) may regulate the Raf/Mek/Erk signal pathway, the role of Hsp90 in pathophysiological cardiac hypertrophy remains unclear. In this study, we examined the role of Hsp90 in this pathway in cardiac hypertrophy under in vivo and in vitro experimental conditions. Cultured rat cardiomyocytes were treated with the Hsp90 inhibitor 17-(allylamino)-17-dimethoxy-geldanamycin (17-AAG) and proteasome inhibitor MG-132, and then incubated with endothelin-1 (ET) to induce hypertrophy of the cells. The ET-induced increase in the cell size was attenuated by 17-AAG pretreatment. Immunoblot analysis revealed that the c-Raf content of ET-treated cardiomyocytes was decreased in the presence of 17-AAG. An increase in phosphorylation levels of Erk1/2 and GATA4 in ET-treated cardiomyocytes was also attenuated by the 17-AAG pretreatment. Myocardial infarction was produced by ligation of the left ventricular coronary artery in rats, and then 17-AAG was intraperitoneally administered to the animals starting from the 2ndweek after coronary artery ligation (CAL). CAL-induced increases in the heart weight and cross-sectional area were attenuated by 17-AAG treatment. CAL rats showed signs of chronic heart failure with cardiac hypertrophy, whereas cardiac function in CAL rats treated with 17-AAG was not reduced. Treatment of CAL rats with 17-AAG caused a decrease in the c-Raf content and Erk1/2 and GATA4 phosphorylation levels. These findings suggest that Hsp90 is involved in the activation of the Raf/Mek/Erk pathway via stabilization of c-Raf in cardiomyocytes, resulting in the development of cardiac hypertrophy following myocardial infarction.

Metabolic control of the proteotoxic stress response: implications in diabetes mellitus and neurodegenerative disorders

Proteome homeostasis, or proteostasis, is essential to maintain cellular fitness and its disturbance is associated with a broad range of human health conditions and diseases. Cells are constantly challenged by various extrinsic and intrinsic insults, which perturb cellular proteostasis and provoke proteotoxic stress. To counter proteomic perturbations and preserve proteostasis, cells mobilize the proteotoxic stress response (PSR), an evolutionarily conserved transcriptional program mediated by heat shock factor 1 (HSF1). The HSF1-mediated PSR guards the proteome against misfolding and aggregation. In addition to proteotoxic stress, emerging studies reveal that this proteostatic mechanism also responds to cellular energy state. This regulation is mediated by the key cellular metabolic sensor AMP-activated protein kinase (AMPK). In this review, we present an overview of the maintenance of proteostasis by HSF1, the metabolic regulation of the PSR, particularly focusing on AMPK, and their implications in the two major age-related diseases-diabetes mellitus and neurodegenerative disorders.