Sigmar1 ablation leads to lung pathological changes associated with pulmonary fibrosis, inflammation, and altered surfactant proteins levels

Sigma1 receptor protein (Sigmar1) is a small, multifunctional molecular chaperone protein ubiquitously expressed in almost all body tissues. This protein has previously shown its cardioprotective roles in rodent models of cardiac hypertrophy, heart failure, and ischemia-reperfusion injury. Extensive literature also suggested its protective functions in several central nervous system disorders. Sigmar1’s molecular functions in the pulmonary system remained unknown. Therefore, we aimed to determine the expression of Sigmar1 in the lungs. We also examined whether Sigmar1 ablation results in histological, ultrastructural, and biochemical changes associated with lung pathology over aging in mice. In the current study, we first confirmed the presence of Sigmar1 protein in human and mouse lungs using immunohistochemistry and immunostaining. We used the Sigmar1 global knockout mouse (Sigmar1−/−) to determine the pathophysiological role of Sigmar1 in lungs over aging. The histological staining of lung sections showed altered alveolar structures, higher immune cells infiltration, and upregulation of inflammatory markers (such as pNFκB) in Sigmar1−/− mice compared to wildtype (Wt) littermate control mice (Wt). This indicates higher pulmonary inflammation resulting from Sigmar1 deficiency in mice, which was associated with increased pulmonary fibrosis. The protein levels of some fibrotic markers, fibronectin, and pSMAD2 Ser 245/250/255 and Ser 465/467, were also elevated in mice lungs in the absence of Sigmar1 compared to Wt. The ultrastructural analysis of lungs in Wt mice showed numerous multilamellar bodies of different sizes with densely packed lipid lamellae and mitochondria with a dark matrix and dense cristae. In contrast, the Sigmar1−/− mice lung tissues showed altered multilamellar body structures in alveolar epithelial type-II pneumocytes with partial loss of lipid lamellae structures in the lamellar bodies. This was further associated with higher protein levels of all four surfactant proteins, SFTP-A, SFTP-B, SFTP-C, and SFTP-D, in the Sigmar1−/− mice lungs. This is the first study showing Sigmar1’s expression pattern in human and mouse lungs and its association with lung pathophysiology. Our findings suggest that Sigmar1 deficiency leads to increased pulmonary inflammation, higher pulmonary fibrosis, alterations of the multilamellar body stuructures, and elevated levels of lung surfactant proteins

SOD2 Deficiency in Cardiomyocytes Defines Defective Mitochondrial Bioenergetics as a Cause of Lethal Dilated Cardiomyopathy

Electrophilic aldehyde (4-hydroxynonenal; 4-HNE), formed after lipid peroxidation, is a mediator of mitochondrial dysfunction and implicated in both the pathogenesis and the progression of cardiovascular disease. Manganese superoxide dismutase (MnSOD), a nuclear-encoded antioxidant enzyme, catalyzes the dismutation of superoxide radicals (O2•-) in mitochondria. To study the role of MnSOD in the myocardium, we generated a cardiomyocyte-specific SOD2 (SOD2Δ) deficient mouse strain. Unlike global SOD2 knockout mice, SOD2Δ mice reached adolescence; however, they die at ~4 months of age due to heart failure. Ultrastructural analysis of SOD2Δ hearts revealed altered mitochondrial architecture, with prominent disruption of the cristae and vacuole formation. Noninvasive echocardiographic measurements in SOD2Δ mice showed dilated cardiomyopathic features such as decreased ejection fraction and fractional shortening along with increased left ventricular internal diameter. An increased incidence of ventricular tachycardia was observed during electrophysiological studies of the heart in SOD2Δ mice. Oxidative phosphorylation (OXPHOS) measurement using a Seahorse XF analyzer in SOD2Δ neonatal cardiomyocytes and adult cardiac mitochondria displayed reduced O2 consumption, particularly during basal conditions and after the addition of FCCP (H+ ionophore/uncoupler), compared to that in SOD2fl hearts. Measurement of extracellular acidification (ECAR) to examine glycolysis in these cells showed a pattern precisely opposite that of the oxygen consumption rate (OCR) among SOD2Δ mice compared to their SOD2fl littermates. Analysis of the activity of the electron transport chain complex identified a reduction in Complex I and Complex V activity in SOD2Δ compared to SOD2fl mice. We demonstrated that a deficiency of SOD2 increases reactive oxygen species (ROS), leading to subsequent overproduction of 4-HNE inside mitochondria. Mechanistically, proteins in the mitochondrial respiratory chain complex and TCA cycle (NDUFS2, SDHA, ATP5B, and DLD) were the target of 4-HNE adduction in SOD2Δ hearts. Our findings suggest that the SOD2 mediated 4-HNE signaling nexus may play an important role in cardiomyopathy

Kv1.1 potassium channel subunit deficiency alters ventricular arrhythmia susceptibility, contractility, and repolarization

Epilepsy-associated Kv1.1 voltage-gated potassium channel subunits encoded by the Kcna1 gene have traditionally been considered absent in heart, but recent studies reveal they are expressed in cardiomyocytes where they could regulate intrinsic cardiac electrophysiology. Although Kv1.1 now has a demonstrated functional role in atria, its role in the ventricles has never been investigated. In this work, electrophysiological, histological, and gene expression approaches were used to explore the consequences of Kv1.1 deficiency in the ventricles of Kcna1 knockout (KO) mice at the organ, cellular, and molecular levels to determine whether the absence of Kv1.1 leads to ventricular dysfunction that increases the risk of premature or sudden death. When subjected to intracardiac pacing, KO mice showed normal baseline susceptibility to inducible ventricular arrhythmias (VA) but resistance to VA under conditions of sympathetic challenge with isoproterenol. Echocardiography revealed cardiac contractile dysfunction manifesting as decreased ejection fraction and fractional shortening. In whole-cell patch-clamp recordings, KO ventricular cardiomyocytes exhibited action potential prolongation indicative of impaired repolarization. Imaging, histological, and transcript analyses showed no evidence of structural or channel gene expression remodeling, suggesting that the observed deficits are likely electrogenic due to Kv1.1 deficiency. Immunoblots of patient heart samples detected the presence of Kv1.1 at relatively high levels, implying that Kv1.1 contributes to human cardiac electrophysiology. Taken together, this work describes an important functional role for Kv1.1 in ventricles where its absence causes repolarization and contractility deficits but reduced susceptibility to arrhythmia under conditions of sympathetic drive

Sigma-1 receptor is involved in modification of ER-mitochondria proximity and Ca2+ homeostasis in cardiomyocytes

The Sigma-1 receptor (Sigmar1) is downregulated in heart failure model mice with mitochondrial dysfunction. However, the mechanism in detail has not been investigated. In this study, we investigated the role of Sigmar1 in ER-mitochondria proximity using Sigmar1-knockdown or -overexpressed neonatal rat ventricular myocytes (NRVMs). The endothelin-1 (ET-1)-induced cardiomyocyte hypertrophy was aggravated with the dysregulation of mitochondrial function and ER-mitochondrial junctional formation in Sigmar1-knockdown NRVMs, whereas improved in Sigmar1 overexpressed NRVMs. Our data suggests that the reduction of the cardiac Sigmar1 results in decrease mitochondrial Ca2+ influx and promotes mitochondrial fission, followed by reduced ER-mitochondria proximity, exacerbating ET-1-induced cardiomyocyte injury

Gut microbiota and microbiota-derived metabolites in cardiovascular diseases.

AbstractCardiovascular diseases, including heart failure, coronary artery disease, atherosclerosis, aneurysm, thrombosis, and hypertension, are a great economic burden and threat to human health and are the major cause of death worldwide. Recently, researchers have begun to appreciate the role of microbial ecosystems within the human body in contributing to metabolic and cardiovascular disorders. Accumulating evidence has demonstrated that the gut microbiota is closely associated with the occurrence and development of cardiovascular diseases. The gut microbiota functions as an endocrine organ that secretes bioactive metabolites that participate in the maintenance of cardiovascular homeostasis, and their dysfunction can directly influence the progression of cardiovascular disease. This review summarizes the current literature demonstrating the role of the gut microbiota in the development of cardiovascular diseases. We also highlight the mechanism by which well-documented gut microbiota-derived metabolites, especially trimethylamine N-oxide, short-chain fatty acids, and phenylacetylglutamine, promote or inhibit the pathogenesis of cardiovascular diseases. We also discuss the therapeutic potential of altering the gut microbiota and microbiota-derived metabolites to improve or prevent cardiovascular diseases