Background: Broad cellular functions and diseases including muscular dystrophy, arrhythmogenic right ventricular cardiomyopathy (ARVC5) and cancer are associated with transmembrane protein43 (TMEM43/LUMA). Objective: The study aimed to investigate biological roles of TMEM43 through genetic regulation, gene pathways and gene networks, candidate interacting genes and up- or down-stream regulators. Methods: Cardiac transcriptomes from 40 strains of recombinant inbred BXD mice and two parental strains representing murine genetic reference population (GRP) was applied for genetic correlation, functional enrichment and co-expression network analysis using systems genetics approach. The results were validated in a newly created knock-in Tmem43-S358L mutation mouse model (Tmem43S358L) that displayed signs of cardiac dysfunction, resembling ARVC5 phenotype seen in humans. Results: We found high Tmem43 levels among BXDs with broad variability in expression. Expression of Tmem43 highly negatively correlated with heart mass and heart rate among BXDs, while levels of Tmem43 highly positively correlated with plasma high density lipoproteins (HDL). Through finding differentially expressed genes (DEGs) between Tmem43S358L mutant and wild type (Tmem43WT) lines, 18 pathways (out of 42 found in BXDs GRP) that are involved in ARVC, Hypertrophic cardiomyopathy, Dilated cardiomyopathy, Non-alcoholic fatty liver disease, Alzheimer disease, Parkinson disease and Huntington disease were verified. We further constructed Tmem43-mediated gene network, in which Ctnna1, Adcy6, Gnas, Ndufs6 and Uqcrc2 were significantly altered in Tmem43S358L mice vs Tmem43WT controls. Conclusions: Our study defined the importance of Tmem43 for cardiac and metabolism related pathways, suggesting that cardiovascular disease-relevant risk factors may also increase risk of metabolic and neurodegenerative diseases via TMEM43-mediated pathways.

Restrictive cardiomyopathy (RCM), a potentially devastating heart muscle disorder, is characterized by diastolic dysfunction due to abnormal muscle relaxation and myocardial stiffness resulting in restrictive filling of the ventricles. Diastolic dysfunction is often accompanied by left atrial or bi-atrial enlargement and normal ventricular size and systolic function. RCM is the rarest form of cardiomyopathy, accounting for 2-5% of pediatric cardiomyopathy cases, however, survival rates have been reported to be 82%, 80%, and 68% at 1-, 2-, and 5-years after diagnosis, respectively. RCM can be idiopathic, familial, or secondary to a systemic disorder, such as amyloidosis, sarcoidosis, and hereditary hemochromatosis. Approximately 30% of cases are familial RCM, and the genes that have been linked to RCM are cTnT, cTnI, MyBP-C, MYH7, MYL2, MYL3, DES, MYPN, TTN, BAG3, DCBLD2, LNMA, and FLNC. Increased Ca 2+ sensitivity, sarcomere disruption, and protein aggregates are some of the few mechanisms of pathogenesis that have been revealed by studies utilizing cell lines and animal models. Additional exploration into the pathogenesis of RCM is necessary to create novel therapeutic strategies to reverse restrictive cardiomyopathic phenotypes.

Studies showed that the gastrointestinal (GI) tract is one of the most important pathways for SARS-CoV-2 infection and coronavirus disease 2019 (COVID-19). As SARS-CoV-2 cellular entry depends on the ACE2 receptor and TMPRSS2 priming of the spike protein, it is important to understand the molecular mechanisms through which these two proteins and their cognate transcripts interact and influence the pathogenesis of COVID-19. In this study, we quantified the expression, associations, genetic modulators, and molecular pathways for Tmprss2 and Ace2 mRNA expressions in GI tissues using a systems genetics approach and the expanded family of highly diverse BXD mouse strains. The results showed that both Tmprss2 and Ace2 are highly expressed in GI tissues with significant covariation. We identified a significant expression quantitative trait locus on chromosome 7 that controls the expression of both Tmprss2 and Ace2. Dhx32 was found to be the strongest candidate in this interval. Co-expression network analysis demonstrated that both Tmprss2 and Ace2 were located at the same module that is significantly associated with other GI-related traits. Protein–protein interaction analysis indicated that hub genes in this module are linked to circadian rhythms. Collectively, our data suggested that genes with circadian rhythms of expression may have an impact on COVID-19 disease, with implications related to the timing and treatment of COVID-19.

Background: The genetic reference population of recombinant inbred BXD mice has been derived from crosses between C57BL/6J and DBA/2J strains. The DBA/2J parent exhibits cardiomyopathy phenotypes, while C57BL/6J has normal heart. BXD mice are sequenced for studying genetic interactions in cardiomyopathies. Objectives: The study aimed to assess cardiomyopathy traits in BXDs and investigate the quantitative genetic architecture of those traits. Methods: Echocardiography, blood pressure, and cardiomyocyte size parameters obtained from 44 strains of BXD family (N >5/sex) at 4-5 months of age were associated with heart transcriptomes and expression quantitative trait loci (eQTL) mapping was performed. Results: More than 2-fold variance in ejection fraction (EF%), fractional shortening (FS%), left ventricular volumes (LVVol), internal dimensions (LVID), mass (LVM), and posterior wall (LVPW) thickness was found among BXDs. In male BXDs, eQTL mapping identified Ndrg4 on chromosome 8 QTL to be positively correlated with LVVol and LVID and negatively associated with cardiomyocyte diameter. In female BXDs, significant eQTLs were found on chromosomes 7 and 3 to be associated with LVPW and EF% and FS%, respectively, and Josd2, Dap3 and Tmp3 were predicted as strong candidate genes. Conclusions: Our study found variable cardiovascular traits among BXD strains and identified multiple associated QTLs, suggesting an influence of genetic background on expression of echocardiographic and cardiomyocyte diameter traits. Increased LVVol and reduced EF% and FS% represented dilated cardiomyopathy, whereas increased LV mass and wall thickness indicated hypertrophic cardiomyopathy traits. The BXD family is ideal for identifying candidate genes, causal and modifier, that influence cardiovascular phenotypes.

Background: The actin-binding sarcomeric nebulette (NEBL) protein provides efficient contractile flexibility via interaction with desmin intermediate filaments. NEBL gene mutations affecting the nebulin repeat (NR) domain is known to induce cardiomyopathy. Objective: The study aimed to explore the roles of NEBL in exercise and biomechanical stress response. Methods: We ablated exon3 encoding the first NR of Nebl and created global Nebl3ex-/3ex- knockout mice. Cardiac function, structure and transcriptome was assessed before and after a 4-week treadmill regimen. A Nebl-based exercise signaling network was constructed using systems genetics methods. H9C2 and neonatal rat cardiomyocytes (NRCs) expressing wild-type or mutant NEBL underwent cyclic mechanical strain. Results: Nebl3ex-/3ex- mice demonstrated diastolic dysfunction with preserved systolic function at 6-months of age. After treadmill running, 4-month-old Nebl3ex-/3ex- mice developed concentric cardiac hypertrophy and left ventricular dilation compared to running Nebl+/+ and sedentary Nebl3ex-/3ex- mice. Disturbance of sarcomeric Z-disks and thin filaments architecture, disruption of intercalated disks and mitochondria were found in exercised Nebl3ex-/3ex- mice. A Nebl-based exercise signaling network included Csrp3, Des, Fbox32, Jup, Myh6, and Myh7. Disturbed expression of TM1, DES, JUP, b-catenin, MLP, α-actinin2 and vinculin proteins was demonstrated. In H9C2 cells, NEBL was recruited into focal adhesions at 24-hours post-strain and redistributed along with F-actin at 72-hours post-strain, suggesting time-dependent redistribution of NEBL in response to strain. NEBL mutations cause desmin disorganization in NRCs upon stretch. Conclusions: Upon stretch, NEBL deficiency causes disturbed sarcomere, Z-disks and desmin organization, and prevents NEBL redistribution to focal adhesions in cardiomyocytes, weakening cardiac tolerance to stress.

Background: The TMEM43/LUMA p.S358L mutation causes arrhythmogenic cardiomyopathy named as ARVC5, a fully penetrant disease with high risk of ventricular arrhythmias, sudden death and heart failure. Male gender and vigorous exercise independently predicted deleterious outcome. Our systems genetics analysis revealed importance of Tmem43 for cardiac and metabolic pathways associated with elevated lipid absorption from small intestine. This study sought to delineate gender specific cardiac, intestinal, and metabolic phenotypes in vivo and investigate underlying pathophysiological mechanisms of S358L mutation. Methods: Serial echocardiography, surface electrocardiography (ECG), treadmill running and body EchoMRI have been utilized in knock-in heterozygous (Tmem43WT/S358L), homozygous (Tmem43S358L) and wildtype (Tmem43WT) littermate mice. Electron microscopy, histology, immunohistochemistry, transcriptome, and protein analysis have been performed in cardiac and intestinal tissues. Results: Systolic dysfunction was apparent in 3-month-old Tmem43S358L and 6-month-old Tmem43WT/S358L mutants. Both mutant lines displayed intolerance to acute stress at 6-months of age, arrhythmias, fibro-fatty infiltration, and subcellular abnormalities in the myocardium. Microarray analysis found significantly differentially expressed genesbetween LV and RV myocardium. Mutants displayed diminished PPARG activities and significantly reduced Tmem43 and b-catenin expression in the heart, while JUP translocated into nuclei of mutant cardiomyocytes. Conversely, elongated villi, fatty infiltration, and overexpression of gut epithelial proliferation markers, b-catenin and Ki-67, were evident in small intestine of mutants. Conclusions: We defined Tmem43 S358L-induced pathological effects on cardiac and intestinal homeostasis viadistinctly disturbed WNT-b-catenin and PPARG signaling thereby contributing to ARVC5 pathophysiology. Results suggest that cardio-metabolic assessment in mutation carriers may be important for predictive and personalized care.

Cardiomyopathy or disease of the heart muscle involves abnormal enlargement and a thickened, stiff, or spongy-like appearance of the myocardium. As a result, the function of the myocardium is weakened and does not sufficiently pump blood throughout the body nor maintain a normal pumping rhythm, leading to heart failure. The main types of cardiomyopathies include dilated hypertrophic, restrictive, arrhythmogenic, and noncompaction cardiomyopathy. Abnormal trabeculations of the myocardium in the left ventricle are classified as left ventricular noncompaction cardiomyopathy (LVNC). Myocardial noncompaction most frequently is observed at the apex of the left ventricle and can be associated with chamber dilation or muscle hypertrophy, systolic or diastolic dysfunction, or both, or various forms of congenital heart disease. Animal models are incredibly important for uncovering the etiology and pathogenesis involved in this disease. This chapter will describe the clinical and pathological features of LVNC in humans and present the animal models that have been used for the study of the genetic basis and pathogenesis of this disease.

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