PERK-Mediated Suppression of microRNAs by Sildenafil Improves Mitochondrial Dysfunction in Heart Failure

Cone photoreceptor phosphodiesterase PDE6H inhibition regulates cancer cell growth and metabolism, replicating the dark retina response

BACKGROUND

PDE6H encodes PDE6γ', the inhibitory subunit of the cGMP-specific phosphodiesterase 6 in cone photoreceptors. Inhibition of PDE6, which has been widely studied for its role in light transduction, increases cGMP levels. The purpose of this study is to characterise the role of PDE6H in cancer cell growth.

METHODS

From an siRNA screen for 487 genes involved in metabolism, PDE6H was identified as a controller of cell cycle progression in HCT116 cells. Role of PDE6H in cancer cell growth and metabolism was studied through the effects of its depletion on levels of cell cycle controllers, mTOR effectors, metabolite levels, and metabolic energy assays. Effect of PDE6H deletion on tumour growth was also studied in a xenograft model.

RESULTS

PDE6H knockout resulted in an increase of intracellular cGMP levels, as well as changes to the levels of nucleotides and key energy metabolism intermediates. PDE6H knockdown induced G1 cell cycle arrest and cell death and reduced mTORC1 signalling in cancer cell lines. Both knockdown and knockout of PDE6H resulted in the suppression of mitochondrial function. HCT116 xenografts revealed that PDE6H deletion, as well as treatment with the PDE5/6 inhibitor sildenafil, slowed down tumour growth and improved survival, while sildenafil treatment did not have an additive effect on slowing the growth of PDE6γ'-deficient tumours.

CONCLUSIONS

Our results indicate that the changes in cGMP and purine pools, as well as mitochondrial function which is observed upon PDE6γ' depletion, are independent of the PKG pathway. We show that in HCT116, PDE6H deletion replicates many effects of the dark retina response and identify PDE6H as a new target in preventing cancer cell proliferation and tumour growth.

Crosstalk between endoplasmic reticulum stress and non-coding RNAs in cardiovascular diseases

Cells are exposed to various pathological stimulus within the cardiovascular system that challenge cells to adapt and survive. Several of these pathological stimulus alter the normal function of the endoplasmic reticulum (ER), leading to the accumulation of unfolded and misfolded proteins, thus triggering the unfolded protein response (UPR) to cope with the stress or trigger apoptosis of damaged cells. Downstream components of the UPR regulate transcription and translation reprogramming to ensure selective gene expression in response to pathological stimulus, including the expression of non-coding RNAs (ncRNAs). The ncRNAs play crucial roles in regulating transcription and translation, and their aberrant expression is associated with the development of cardiovascular disease (CVD). Notably, ncRNAs and ER stress can modulate each other and synergistically affect the development of CVD. Therefore, studying the interaction between ER stress and ncRNAs is necessary for effective prevention and treatment of CVD. In this review, we discuss the UPR signaling pathway and ncRNAs followed by the interplay regulation of ER stress and ncRNAs in CVD, which provides further insights into the understanding of the pathogenesis of CVD and therapeutic strategies. This article is categorized under: RNA in Disease and Development > RNA in Disease.

LncRNAs and CircRNAs in Endoplasmic Reticulum Stress: A Promising Target for Cardiovascular Disease?

The endoplasmic reticulum (ER) is a principal subcellular organelle responsible for protein quality control in the secretory pathway, preventing protein misfolding and aggregation. Failure of protein quality control in the ER triggers several molecular mechanisms such as ER-associated degradation (ERAD), the unfolded protein response (UPR) or reticulophagy, which are activated upon ER stress (ERS) to re-establish protein homeostasis by transcriptionally and translationally regulated complex signalling pathways. However, maintenance over time of ERS leads to apoptosis if such stress cannot be alleviated. The presence of abnormal protein aggregates results in loss of cardiomyocyte protein homeostasis, which in turn results in several cardiovascular diseases such as dilated cardiomyopathy (DCM) or myocardial infarction (MI). The influence of a non-coding genome in the maintenance of proper cardiomyocyte homeostasis has been widely proven. To date, the impact of microRNAs in molecular mechanisms orchestrating ER stress response has been widely described. However, the role of long noncoding RNAs (lncRNAs) and circular RNAs (circRNAs) is just beginning to be addressed given the potential role of these RNA classes as therapeutic molecules. Here, we provide a current state-of-the-art review of the roles of distinct lncRNAs and circRNAs in the modulation of ERS and UPR and their impact in cardiovascular diseases.

miR-181c targets Parkin and SMAD7 in human cardiac fibroblasts: Validation of differential microRNA expression in patients with diabetes and heart failure with preserved ejection fraction

BACKGROUND

Cardiac fibrosis represents a key feature in the pathophysiology of heart failure with preserved ejection fraction (HFpEF), a condition highly prevalent amongst geriatric patients, especially if diabetic. The microRNA miR-181c has been shown to be associated with the response to exercise training in HFpEF patients and has been also linked to diabetic cardiovascular complications. However, the underlying mechanisms have not been fully elucidated.

OBJECTIVE

To measure circulating miR-181c in elderly patients with HFpEF and DM and identify gene targets pathophysiologically relevant in HFpEF.

METHODS

We quantified circulating miR-181c in frail older adults with a confirmed diagnosis of HFpEF and diabetes, and, as control, we enrolled age-matched subjects without HFpEF and without diabetes. We validated in human cardiac fibroblasts the molecular mechanisms linking miR-181c to a pro-fibrotic response.

RESULTS

51 frail patients were included (34 patients with diabetes and HFpEF and 17 age-matched controls. We observed that miR-181c was significantly upregulated (p<0.0001) in HFpEF patients vs controls. We confirmed in vitro that miR-181c is targeting PRKN and SMAD7.

CONCLUSIONS

We demonstrate that miR-181c levels are significantly increased in frail elderly adults with diabetes and HFpEF and that miR-181c targets PRKN and SMAD7 in human cardiac fibroblasts.

Crosstalk between microRNA and Oxidative Stress in Heart Failure: A Systematic Review

Heart failure is defined as a clinical syndrome consisting of key symptoms and is due to a structural and/or functional alteration of the heart that results in increased intracardiac pressures and/or inadequate cardiac output at rest and/or during exercise. One of the key mechanisms determining myocardial dysfunction in heart failure is oxidative stress. MicroRNAs (miRNAs, miRs) are short, endogenous, conserved, single-stranded non-coding RNAs of around 21-25 nucleotides in length that act as regulators of multiple processes. A systematic review following the PRISMA guidelines was performed on the evidence on the interplay between microRNA and oxidative stress in heart failure. A search of Pubmed, Embase, Scopus, and Scopus direct databases using the following search terms: 'heart failure' AND 'oxidative stress' AND 'microRNA' or 'heart failure' AND 'oxidative stress' AND 'miRNA' was conducted and resulted in 464 articles. Out of them, 15 full text articles were eligible for inclusion in the qualitative analysis. Multiple microRNAs are involved in the processes associated with oxidative stress leading to heart failure development including mitochondrial integrity and function, antioxidant defense, iron overload, ferroptosis, and survival pathways.

Neuron-specific translational control shift ensures proteostatic resilience during ER stress

Proteostasis is essential for cellular survival and particularly important for highly specialised post‐mitotic cells such as neurons. Transient reduction in protein synthesis by protein kinase R‐like endoplasmic reticulum (ER) kinase (PERK)‐mediated phosphorylation of eukaryotic translation initiation factor 2α (p‐eIF2α) is a major proteostatic survival response during ER stress. Paradoxically, neurons are remarkably tolerant to PERK dysfunction, which suggests the existence of cell type‐specific mechanisms that secure proteostatic stress resilience. Here, we demonstrate that PERK‐deficient neurons, unlike other cell types, fully retain the capacity to control translation during ER stress. We observe rescaling of the ATF4 response, while the reduction in protein synthesis is fully retained. We identify two molecular pathways that jointly drive translational control in PERK‐deficient neurons. Haem‐regulated inhibitor (HRI) mediates p‐eIF2α and the ATF4 response and is complemented by the tRNA cleaving RNase angiogenin (ANG) to reduce protein synthesis. Overall, our study elucidates an intricate back‐up mechanism to ascertain translational control during ER stress in neurons that provides a mechanistic explanation for the thus far unresolved observation of neuronal resilience to proteostatic stress.

Endoplasmic Reticulum Stress and miRNA Impairment in Aging and Age-Related Diseases

Aging is a physiological process defined by decreased cellular and tissue functions. Reduced capacity of protein degradation is one of the important hallmarks of aging that may lead to misfolded protein accumulation and progressive loss of function in organ systems. Recognition of unfolded/misfolded protein aggregates via endoplasmic reticulum (ER) stress sensors activates an adaptive mechanism, the unfolded protein response (UPR). The initial step of UPR is defined by chaperone enhancement, ribosomal translation suppression, and misfolded protein degradation, while prolonged ER stress triggers apoptosis. MicroRNAs (miRNAs) are non-coding RNAs affecting various signaling pathways through degradation or translational inhibition of targeted mRNAs. Therefore, UPR and miRNA impairment in aging and age-related diseases is implicated in various studies. This review will highlight the recent insights in ER stress–miRNAs alterations during aging and age-related diseases, including metabolic, cardiovascular, and neurodegenerative diseases and several cancers.

Inhibition of cardiac PERK signaling promotes peripartum cardiac dysfunction

Peripartum cardiomyopathy (PPCM) is a life-threatening heart failure occurring in the peripartum period. Although mal-angiogenesis, induced by the 16-kDa N-terminal prolactin fragment (16 K PRL), is involved in the pathogenesis, the effect of full-length prolactin (23 K PRL) is poorly understood. We transfected neonate rat cardiomyocytes with plasmids containing 23 K PRL or 16 K PRL in vitro and found that 23 K PRL, but not 16 K PRL, upregulated protein kinase RNA-like endoplasmic reticulum kinase (PERK) signaling, and hypoxia promoted this effect. During the perinatal period, cardiomyocyte-specific PERK homogenous knockout (CM-KO) mice showed PPCM phenotypes after consecutive deliveries. Downregulation of PERK or JAK/STAT signaling and upregulation of apoptosis were observed in CM-KO mouse hearts. Moreover, in bromocriptine-treated CM-KO mice, cardiac function did not improve and cardiomyocyte apoptosis was not suppressed during the peripartum period. These results demonstrate that interaction between 23 K PRL and PERK signaling is cardioprotective during the peripartum term.

Endoplasmic reticulum stress and unfolded protein response in cardiovascular diseases

Cardiovascular diseases (CVDs), such as ischaemic heart disease, cardiomyopathy, atherosclerosis, hypertension, stroke and heart failure, are among the leading causes of morbidity and mortality worldwide. Although specific CVDs and the associated cardiometabolic abnormalities have distinct pathophysiological and clinical manifestations, they often share common traits, including disruption of proteostasis resulting in accumulation of unfolded or misfolded proteins in the endoplasmic reticulum (ER). ER proteostasis is governed by the unfolded protein response (UPR), a signalling pathway that adjusts the protein-folding capacity of the cell to sustain the cell's secretory function. When the adaptive UPR fails to preserve ER homeostasis, a maladaptive or terminal UPR is engaged, leading to the disruption of ER integrity and to apoptosis. ER stress functions as a double-edged sword, with long-term ER stress resulting in cellular defects causing disturbed cardiovascular function. In this Review, we discuss the distinct roles of the UPR and ER stress response as both causes and consequences of CVD. We also summarize the latest advances in our understanding of the importance of the UPR and ER stress in the pathogenesis of CVD and discuss potential therapeutic strategies aimed at restoring ER proteostasis in CVDs.

PERK inhibition attenuates vascular remodeling in pulmonary arterial hypertension caused by BMPR2 mutation

Pulmonary arterial hypertension (PAH) is a fatal disease characterized by excessive pulmonary vascular remodeling. However, despite advances in therapeutic strategies, patients with PAH bearing mutations in the bone morphogenetic protein receptor type 2 (BMPR2)-encoding gene present severe phenotypes and outcomes. We sought to investigate the effect of PER-like kinase (PERK), which participates in one of three major pathways associated with the unfolded protein response (UPR), on PAH pathophysiology in BMPR2 heterozygous mice. BMPR2 heterozygosity in pulmonary artery smooth muscle cells (PASMCs) decreased the abundance of the antiapoptotic microRNA miR124-3p through the arm of the UPR mediated by PERK. Hypoxia promoted the accumulation of unfolded proteins in BMPR2 heterozygous PASMCs, resulting in increased PERK signaling, cell viability, cellular proliferation, and glycolysis. Proteomic analyses revealed that PERK ablation suppressed PDGFRβ-STAT1 signaling and glycolysis in hypoxic BMPR2 heterozygous PASMCs. Furthermore, PERK ablation or PERK inhibition ameliorated pulmonary vascular remodeling in the Sugen/chronic hypoxia model of PAH, irrespective of BMPR2 status. Hence, these findings suggest that PERK inhibition is a promising therapeutic strategy for patients with PAH with or without BMPR2 mutation.