A Common Missense Variant in OMA1 Associated with the Prognosis of Heart Failure

Mitochondrial proteases modulate mitochondrial stress signalling and cellular homeostasis in health and disease

Maintenance of mitochondrial homeostasis requires a plethora of coordinated quality control and adaptations' mechanisms in which mitochondrial proteases play a key role. Their activation or loss of function reverberate beyond local mitochondrial biochemical and metabolic remodelling into coordinated cellular pathways and stress responses that feedback onto the mitochondrial functionality and adaptability. Mitochondrial proteolysis modulates molecular and organellar quality control, metabolic adaptations, lipid homeostasis and regulates transcriptional stress responses. Defective mitochondrial proteolysis results in disease conditions most notably, mitochondrial diseases, neurodegeneration and cancer. Here, it will be discussed how mitochondrial proteases and mitochondria stress signalling impact cellular homeostasis and determine the cellular decision to survive or die, how these processes may impact disease etiopathology, and how modulation of proteolysis may offer novel therapeutic strategies.

A common variant in PIK3CG gene associated with the prognosis of heart failure

Phosphoinositide 3-kinase γ (PI3Kγ) is G-protein-coupled receptor-activated lipid kinase with both kinase-dependent and kinase-independent activity. Plenty of evidence have demonstrated that PI3Kγ participated in TAC and I/R-induced myocardial remodelling and heart failure (HF). In this study, we tested the hypothesis that common variants in the PI3Kγ gene (PIK3CG) were associated with the prognosis of HF in the Chinese Han population. Through re-sequencing and genotyping, we finally identified a common variant in the 3'UTR of PIK3CG strongly associated with the prognosis of HF in two-stage population: adjusted p = 0.007, hazard ratio = 0.56 (0.36-0.85) in the first cohort and adjusted p = 0.024, hazard ratio = 0.39 (0.17-0.88) in the replicated cohort. A series of functional assays revealed that rs10215499-A allele suppressed PIK3CG translation by facilitating has-miR-133a-3p binding, but not the G allele. Subjects carrying the GG genotype showed higher mRNA and protein level than those with AA and AG genotype. Furthermore, overexpression of PIK3CG could protect AC16 from hypoxia/reoxygenation (H/R)-induced apoptosis, while the case was opposite for PIK3CG silencing. In conclusion, common variant rs10215499 in the 3'-UTR of PIK3CG might affect the prognosis of HF by interfering with miR-133a-3p binding and PIK3CG is a promising target for HF treatment in the future.

The Prognostic Value of Blood Urea Nitrogen to Albumin Ratio on Patients with Heart Failure

This study aimed to investigate the relationship between blood urea nitrogen to albumin ratio (BAR) and the prognosis of heart failure (HF).A total of 2125 patients with HF were included in this single-center prospective cohort study between February 2012 and December 2017. Using a receiver operating characteristic curve, we determined the cutoff value of BAR as 0.24. All patients were divided into two groups according to the cutoff value of BAR.Among 2125 HF patients, the mean age was 56.7 ± 14.3. During a median follow-up time of 22 months, 516 end-point events occurred. Compared with patients in the low BAR group, those in the high BAR group were older; more likely to be male; had a higher percentage of hypertension, diabetes, smoking, and β-blocker use; and higher levels of alanine aminotransferase, glycosylated hemoglobin, creatinine, log-transformed NTproBNP, and Blood urea nitrogen but lower levels of albumin, triglycerides, high-density lipoprotein, ApoA1, and hemoglobin. Prognosis analysis indicated that high BAR was associated with increased mortality risk of HF (Hazard Ratio = 1.497, 95% CI = 1.234-1.816; P < 0.001) in the multivariate Cox proportional hazard regression model. Subgroup analysis revealed that stratification by age, gender, history of hypertension, diabetes, smoking, β-blocker use, and levels of hemoglobin, glycosylated hemoglobin, and creatinine have no obvious effect on the association between BAR ratio and the prognosis of HF. Furthermore, patients with high BAR represented a decreased left ventricular ejection fraction and increased left ventricular end-diastolic diameter.High BAR was an independent predictor for the mortality risk of HF.

Association between MMP2 gene polymorphisms and dilated cardiomyopathy in a Chinese Han population

AIMS

Dilated cardiomyopathy (DCM) belongs to the common types of cardiomyopathies. The pathogenesis remains unclear despite the fact that various genes have been found associated with DCM. MMP2 is a zinc-dependent and calcium-containing secreted endoproteinases, which could cleave a broad spectrum of substrates including extracellular matrix components and cytokines. It has proved to play an important role in the cardiovascular diseases. This study aimed to investigate the potential role of MMP2 gene polymorphisms in DCM susceptibility and prognosis in a Chinese Han population.

METHODS AND RESULTS

A total of 600 idiopathic DCM patients and 700 healthy controls were enrolled. Patients with contact information were followed up for a median period of 28 months. Three tagged single nucleotide polymorphisms (rs243865, rs2285052, and rs2285053) in the promoter of MMP2 gene were genotyped. A series of function analysis were conducted to illuminate the underlying mechanism. The frequency of rs243865-C allele was increased in DCM patients when compared with healthy controls (P = 0.001). Genotypic frequencies of rs243865 were associated with the susceptibility of DCM in the codominant, dominant, and overdominant models (P < 0.05). Besides, rs243865-C allele presented a correlation with the poor prognosis of DCM patients in both dominant (HR = 2.0, 95% confidence interval [CI] = 1.14-3.57, P = 0.017) and additive (HR = 1.85, 95% CI = 1.09-3.13, P = 0.02) model. The statistical significance remained after adjustment for sex, age, hypertension, diabetes, hyperlipidaemia, and smoking status. There were significant differences in left ventricular end-diastolic diameter and left ventricular ejection fraction between rs243865-CC and CT genotypes. Functional analysis indicated that rs243865-C allele increased luciferase activity and the mRNA expression level of MMP2 by facilitating ZNF354C binding.

CONCLUSIONS

Our study suggested that MMP2 gene polymorphisms were associated with DCM susceptibility and prognosis in the Chinese Han population.

Multivariable prognostic model for heart failure in Chinese Han population-based setting

Aims

The prognosis of heart failure (HF) depends on genetic predisposition, and recent studies have shown that impaired autophagy is involved in HF. This study was aimed to construct a prognostic model combining polygenetic background based on the autophagy pathway and other traditional risk factors (TRF) of HF prognosis.

Methods and results

Via re‐analysing the transcriptomic data of 50 failing and 14 non‐failing donors, differentially expressed autophagy‐related genes (ARGs) were chosen for further comparison and analysis with whole exome sequencing and follow‐up data of 1000 HF patients. By searching from reported articles, prognosis‐related polymorphisms were identified. ARGs and prognosis‐related polymorphisms were used to develop genetic risk score (GRS) and genetic risk factor (GRF), respectively. We compared the predictive power of five models [Model 1, GRS; Model 2, composite of TRF and N‐terminal B‐type natriuretic peptide (NT‐proBNP); Model 3, composite of TRF, NT‐proBNP, and GRS; Model 4, composite of TRF, NT‐proBNP, and GRF; and Model 5, composite of TRF, NT‐proBNP, GRF, and GRS] by applying receiver operating characteristic curves. Twenty‐four prognosis‐related polymorphisms were used to construct GRF and 11 variants among 48 differentially expressed ARGs associated with clinical outcomes of HF patients were applied for GRS. GRS was strongly associated with cardiac mortality of HF patients, independent of TRF and GRF (95% confidence interval 1.273–1.739, P = 5.78 × 10⁻⁷). Comparing with patients with lowest GRS tertile, those with highest tertile had higher risks of developing worse clinical outcomes (hazard ratio = 1.866; 95% confidence interval 1.352–2.575, P = 1.47 × 10⁻⁴). The discrimination power of the model including GRS, TRF, GRF, and NT‐proBNP is most considerable (area under curve = 0.777), especially in men, patients over 60, patients with hypertension, patients without diabetes or hyperlipidaemia.

Conclusions

The model combining autophagy‐related GRS, TRF, GRF, and NT‐proBNP performs well in distinguishing between worse‐prognosis and better‐prognosis HF patients, leading a promising strategy for HF treatment and HF prevention.

Recent advances in, and challenges of, designing OMA1 drug screens

The proteases of the mitochondrial inner membrane are challenging yet highly desirable drug targets for complex, multifactorial diseases prevalent mainly in the elderly. Among them, OMA1 with its substrates OPA1 and DELE1 safeguards mitochondrial homeostasis at the intersection of energy metabolism and apoptosis, which may have relevance for neurodegeneration, malignancy and heart failure, among other diseases. Little is known about OMA1. Its structure has not been solved and we are just beginning to understand the enzyme's context-dependent regulation. OMA1 appears dormant under physiological conditions as judged by OPA1's processing pattern. The protease is rapidly activated, however, when cells experience stress or undergo apoptosis. Intriguingly, genetic OMA1 ablation can delay or even prevent apoptosis in animal models for diseases that can be broadly categorized as ischemia-reperfusion related disorders. Three groups have reported their efforts implementing OMA1 drug screens. This article reviews some of the technical challenges encountered in these assays and highlights what can be learned for future screening campaigns, and about the OMA1 protease more broadly. OMA1 does not exists in a vacuum and potent OMA1 inhibitors are needed to tease apart OMA1's intricate interactions with the other mitochondrial proteases and enzymes. Furthermore, OMA1 inhibitors hold the promise of becoming a new class of cytoprotective medicines for disorders influenced by dysfunctional mitochondria, such as heart failure or Alzheimer's Disease.

OMA1 High-Throughput Screen Reveals Protease Activation by Kinase Inhibitors

Mitochondrial proteases are interesting but challenging drug targets for multifactorial diseases, such as neurodegeneration and cancer. The mitochondrial inner membrane protease OMA1 is a bona fide drug target for heart failure supported by data from human linkage analysis and animal disease models, but presumably relevant for more indications. OMA1 acts at the intersection of energy metabolism and stress signaling. The protease cleaves the structural protein OPA1, which organizes the cristae, as well as the signaling peptide DELE1, which can stimulate the integrated stress response. OMA1 shows little activity under physiological conditions but hydrolyzes OPA1 in mitochondria destined for mitophagy and during apoptosis. Little is known about OMA1, its structure has not been solved, let alone its context-dependent regulation. Autocatalytic processing and the lack of OMA1 inhibitors are thereby creating the biggest roadblocks. This study introduces a scalable, cellular OMA1 protease assay suitable for high-throughput drug screening. The assay utilizes an engineered luciferase targeted to the inner membrane as artificial OMA1 substrate, whereby the reporter signal inversely correlates to OMA1 activity. Testing different screening protocols and sampling different compound collections validated the reporter and demonstrated that both OMA1 activators as well as OMA1 inhibitors can be identified with the assay. Ten kinase-targeted cancer drugs triggered OMA1 in the assays, which suggests─considering cardiotoxicity as a rather common side-effect of this class of drugs─cross-reactivity with the OMA1 pathway.