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MCUb upregulation in the type 2 diabetic heart impacts cardiac function by altering mitochondrial metabolic fuel flux and the cardiac myocyte phosphoproteome

ABSTRACT: Mitochondrial Ca2+ (mCa2+) plays an important role in regulating cardiac metabolism and physiology. However, its contribution to metabolic and functional defects in the hearts of type 2 diabetic mice (T2D) is not well understood. Ca2+ is imported into mitochondria by the mitochondrial calcium uniporter complex (MCUC) which is a highly selective multimeric Ca2+ ion channel composed of pore-forming, scaffold, and regulatory subunits. Here, we describe new mechanisms involving the MCUC inhibitory subunit MCUb and its role in determining cardiac dysfunction by linking cardiac mitochondrial metabolism and contractile function. Hearts from T2D mice were analyzed 5 months following a single streptozotocin (STZ) injection (75 mg/kg) and high fat diet (HFD) feeding, and compared to control hearts from mice fed normal chow. Transcriptional and proteomic profiling were employed to characterize these hearts. Regulation of MCUb gene expression was investigated using a recombinant mutant inactive Cas9 (dCas9)-based gene promoter pull down approach coupled with mass spectrometry (MS). A dominant negative MCUb (MCUb W246R/V251E=dnMCUb) was engineered. dnMCUb was biochemically characterized in vitro, tested in neonatal cardiac myocytes exposed to culture media mimicking the diabetic milieu, and expressed in type 2 diabetic mice for 1 month. The impact of dnMCUb on the cardiac physiology was then investigated using omics as well as functional approaches aimed to highlight metabolic and contractile features. RNA-seq and proteomics analysis revealed that T2D hearts relied almost exclusively on fatty acid oxidative metabolism. In parallel we found a significant increase in MCUb mRNA and protein in T2D hearts, which was associated with decreased mCa2+ import rates. MS analysis of proteins co-precipitated with dCas9 revealed the presence of NCOR2 in control but not in T2D MCUb gene promoters. Downregulation of NCOR2 in isolated cardiac myocytes from control mice recapitulated the increase in MCUb gene expression. The dnMCUb mutant increased MCUC Ca2+ affinity by improving the architecture of the complex. Furthermore, when dnMCUb was introduced to cardiac myocytes and T2D mice we observed increased mitochondrial glucose oxidation, mitochondrial ATP production, and enhanced cardiac function. These were linked to the complete restoration of phospholamban (PLN) phosphorylation via Protein Kinase A (PKA) as revealed by both MS analysis of the phosphoproteome and studies dedicated on PLN only followed by PKA pharmacological inhibition. We detail a new pathological axis in which T2D induces global metabolic adaptations and inflexibility in part due to impaired mCa2+ transport into the mitochondrial matrix, resulting from MCUb overexpression. Moreover, we describe a mCa2+-dependent regulation of cytosolic Ca2+ (cCa2+) trafficking in which mCa2+ regulates the activity of SERCA2a via PKA-dependent phosphorylation of PLN.

ORGANISM(S): Mus musculus

PROVIDER: GSE145294 | GEO | 2022/12/15

REPOSITORIES: GEO

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Project description:Background: The phospholamban (PLN) p.Arg14del mutation belongs to the established causes of dilated cardiomyopathy, with the molecular disease mechanisms incompletely understood. We used human induced pluripotent stem cell (hiPSC)-derived cardiomyocytes, CRISPR/Cas9 gene editing and patient heart samples to investigate the molecular pathomechanisms of PLN p.Arg14del cardiomyopathy. Methods and results: Patient dermal fibroblasts carrying the PLN p.Arg14del mutation were reprogrammed into hiPSC, isogenic controls were established by CRISPR/Cas9. Cells were differentiated into cardiomyocytes and characterized in 2D and 3D-engineered heart tissue (EHT) format. Mutant cardiomyocytes revealed significantly prolonged Ca2+ transient decay time, Ca2+-load dependent irregular beating pattern and lower peak force compared to isogenic controls. While this data support the reported super-inhibitory effect of PLN p.Arg14del on the sarcoplasmic/endoplasmic reticulum Ca2+ ATPase, an unchanged SR Ca2+ content argued against disturbed SR Ca2+ cycling as the sole cause of contractile dysfunction. Label-free proteomic analysis of p.Arg14del EHTs revealed less endoplasmic reticulum (ER), ribosomal and mitochondrial proteins. Electron microscopy showed dilation of the rough ER, large lipid droplets in close association with mitochondria and reduced mitochondrial number. Follow-up experiments confirmed impairment of the rough ER/mitochondria compartment and enhanced oxidative stress in PLN p.Arg14del. Relevance for human disease was demonstrated by immunohistochemistry of human heart samples. PLN p.Arg14del end-stage heart failure samples revealed perinuclear aggregates positive for ER marker proteins and oxidative stress in comparison to ischemic heart failure - and non-failing donor heart samples. Surprisingly, transduction of PLN p.Arg14del EHTs with the Ca2+ binding protein GCaMP6f reversed the contractile, molecular and morphological disease phenotype. Conclusion: This study identified impairment of the rough ER/mitochondria compartment without SR dysfunction as a novel disease mechanism underlying PLN p.Arg14del cardiomyopathy. The pathology was improved by Ca2+-scavenging, suggesting impaired local Ca2+ cycling as an important disease culprit.

Project description:The incidence of type 2 diabetes (T2D) is increasing globally, with long-term implications for human health and longevity. Heart disease is the leading cause of death in T2D patients, who display an elevated risk of an acute cardiovascular event and worse outcomes following such an insult. The underlying mechanisms that predispose the diabetic heart to this poor prognosis remain to be defined. This study developed a pre-clinical model (Rattus norvegicus) that complemented caloric excess from a high-fat diet (HFD) and pancreatic β-cell dysfunction from streptozotocin (STZ) to produce hyperglycaemia, peripheral insulin resistance, hyperlipidaemia and elevated fat mass to mimic the clinical features of T2D. Ex vivo cardiac function was assessed using Langendorff perfusion with systolic and diastolic contractile depression observed in T2D hearts. Cohorts representing untreated, individual HFD- or STZ-treatments and the combined HFD+STZ approach were used to generate ventricular samples (n=9 per cohort) for sequential and integrated analysis of the proteome, lipidome and metabolome by liquid chromatography-tandem mass spectrometry. This study found that in T2D hearts, HFD treatment primed the metabolome, while STZ treatment was the major driver for changes in the proteome. Both treatments equally impacted the lipidome. Our data suggest that increases in β-oxidation and early TCA cycle intermediates promoted rerouting via 2-oxaloacetate to glutamate, γ aminobutyric acid and glutathione. Furthermore, we suggest that the T2D heart activates networks to redistribute excess acetyl-CoA towards ketogenesis and incomplete β-oxidation through the formation of short-chain acylcarnitine species. Multi-omics provided a global and comprehensive molecular view of the diabetic heart, which distributes substrates and products from excess β-oxidation, reduces metabolic flexibility and impairs capacity to restore high energy reservoirs needed to respond to and prevent subsequent acute cardiovascular events.

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MCUb upregulation in the type 2 diabetic heart impacts cardiac function by altering mitochondrial metabolic fuel flux and the cardiac myocyte phosphoproteome

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