Diabetic cardiomyopathy is associated with increased risk of heart failure in type 1 diabetic patients. Mitochondrial dysfunction is suggested as an underlying contributor to diabetic cardiomyopathy. Cardiac mitochondria are characterized by subcellular spatial locale, including mitochondria located beneath the sarcolemma, subsarcolemmal mitochondria (SSM), and mitochondria situated between the myofibrils, interfibrillar mitochondria (IFM). The goal of this study was to determine whether type 1 diabetic insult in the heart influences proteomic make-up of spatially distinct mitochondrial subpopulations and to evaluate the role of nuclear encoded mitochondrial protein import. Utilizing multiple proteomic approaches (iTRAQ and two-dimensional-differential in-gel electrophoresis), IFM proteomic make-up was impacted by type 1 diabetes mellitus to a greater extent than SSM, as evidenced by decreased abundance of fatty acid oxidation and electron transport chain proteins. Mitochondrial phosphate carrier and adenine nucleotide translocator, as well as inner membrane translocases, were decreased in the diabetic IFM ( P < 0.05 for both). Mitofilin, a protein involved in cristae morphology, was diminished in the diabetic IFM ( P < 0.05). Posttranslational modifications, including oxidations and deamidations, were most prevalent in the diabetic IFM. Mitochondrial heat shock protein 70 (mtHsp70) was significantly decreased in diabetic IFM ( P < 0.05). Mitochondrial protein import was decreased in the diabetic IFM with no change in the diabetic SSM ( P < 0.05). Taken together, these results indicate that mitochondrial proteomic alterations in the type 1 diabetic heart are more pronounced in the IFM. Further, proteomic alterations are associated with nuclear encoded mitochondrial protein import dysfunction and loss of an essential mitochondrial protein import constituent, mtHsp70, implicating this process in the pathogenesis of the diabetic heart.

Background Cardiomyocytes are rich in mitochondria which are situated in spatially-distinct subcellular regions including those under the plasma membrane, subsarcolemmal mitochondria; and those between the myofibrils, interfibrillar mitochondria. We previously observed subpopulation-specific differences in mitochondrial proteomes following diabetic insult. The objective of this study was to determine whether mitochondrial genome-encoded proteins are regulated by microRNAs inside the mitochondrion and whether subcellular spatial location or diabetes mellitus influences the dynamics. Methods and Results Using microarray technology coupled with cross-linking immunoprecipitation and next generation sequencing, we identified a pool of mitochondrial microRNAs, termed mitomiRs that are redistributed in spatially-distinct mitochondrial subpopulations in an inverse manner following diabetic insult. Redistributed mitomiRs displayed distinct interactions with the mitochondrial genome requiring specific stoichiometric associations with RISC constituents argonaute-2 (Ago2) and fragile X mental retardation–related protein 1 (FXR1) for translational regulation. In the presence of Ago2 and FXR1, redistribution of mitomiR-378 to the IFM following diabetic insult led to down regulation of mitochondrially-encoded F0 component ATP6. Next generation sequencing analyses identified specific transcriptome and mitomiR sequences associated with ATP6 regulation. Overexpression of mitomiR-378 in HL-1 cells resulted in its accumulation in the mitochondrion and down-regulation of functional ATP6 protein, while antagomir blockade restored functional ATP6 protein and cardiac pump function. Conclusions We propose mitomiRs can translationally regulate mitochondrially-encoded proteins in spatially-distinct mitochondrial subpopulations during diabetes mellitus. The results reveal the requirement of RISC constituents in the mitochondrion for functional mitomiR translational regulation and provide a connecting link between diabetic insult and ATP synthase function.

JM. Enhanced apoptotic propensity in diabetic cardiac mitochondria: influence of subcellular spatial location. Am J Physiol Heart Circ Physiol 298: H633-H642, 2010. First published December 4, 2009 doi:10.1152/ajpheart.00668.2009.-Cardiovascular complications, such as diabetic cardiomyopathy, account for the majority of deaths associated with diabetes mellitus. Mitochondria are particularly susceptible to the damaging effects of diabetes mellitus and have been implicated in the pathogenesis of diabetic cardiomyopathy. Cardiac mitochondria consist of two spatially distinct subpopulations, termed subsarcolemmal mitochondria (SSM) and interfibrillar mitochondria (IFM). The goal of this study was to determine whether subcellular spatial location is associated with apoptotic propensity of cardiac mitochondrial subpopulations during diabetic insult. Swiss Webster mice were subjected to intraperitoneal injection of streptozotocin or citrate saline vehicle. Ten weeks following injection, diabetic hearts displayed increased caspase-3 and caspase-9 activities, indicating enhanced apoptotic signaling (P Ͻ 0.05, for both). Mitochondrial size (forward scatter) and internal complexity (side scatter) were decreased in diabetic IFM (P Ͻ 0.05, for both) but not in diabetic SSM. Mitochondrial membrane potential (⌬ ⌿m) was lower in diabetic IFM (P Ͻ 0.01) but not in diabetic SSM. Mitochondrial permeability transition pore (mPTP) opening was increased in diabetic compared with control IFM (P Ͻ 0.05), whereas no differences were observed in diabetic compared with control SSM. Examination of mPTP constituents revealed increases in cyclophilin D in diabetic IFM. Furthermore, diabetic IFM possessed lower cytochrome c and BcL-2 levels and increased Bax levels (P Ͻ 0.05, for all 3). No significant changes in these proteins were observed in diabetic SSM compared with control. These results indicate that diabetes mellitus is associated with an enhanced apoptotic propensity in IFM, suggesting a differential apoptotic susceptibility of distinct mitochondrial subpopulations based upon subcellular location.

Baseler WA, Thapa D, Jagannathan R, Dabkowski ER, Croston TL, Hollander JM. miR-141 as a regulator of the mitochondrial phosphate carrier (Slc25a3) in the type 1 diabetic heart.

Mitochondrial dysfunction is a contributor to diabetic cardiomyopathy. Previously, we observed proteomic decrements within the inner mitochondrial membrane (IMM) and matrix of diabetic cardiac interfibrillar mitochondria (IFM) correlating with dysfunctional mitochondrial protein import. The goal of this study was to determine whether overexpression of mitochondria phospholipid hydroperoxide glutathione peroxidase 4 (mPHGPx), an antioxidant enzyme capable of scavenging membrane-associated lipid peroxides in the IMM, could reverse proteomic alterations, dysfunctional protein import, and ultimately, mitochondrial dysfunction associated with the diabetic heart. MPHGPx transgenic mice and controls were made diabetic by multiple low-dose streptozotocin injections and examined after 5 wk of hyperglycemia. Five weeks after hyperglycemia onset, in vivo analysis of cardiac contractile function revealed decreased ejection fraction and fractional shortening in diabetic hearts that was reversed with mPHGPx overexpression. MPHGPx overexpression increased electron transport chain function while attenuating hydrogen peroxide production and lipid peroxidation in diabetic mPHGPx IFM. MPHGPx overexpression lessened proteomic loss observed in diabetic IFM. Posttranslational modifications, including oxidations and deamidations, were attenuated in diabetic IFM with mPHGPx overexpression. Mitochondrial protein import dysfunction in diabetic IFM was reversed with mPHGPx overexpression correlating with protein import constituent preservation. Ingenuity Pathway Analyses indicated that oxidative phosphorylation, tricarboxylic acid cycle, and fatty acid oxidation processes most influenced in diabetic IFM were preserved by mPHGPx overexpression. Specific mitochondrial networks preserved included complex I and II, mitochondrial ultrastructure, and mitochondrial protein import. These results indicate that mPHGPx overexpression can preserve the mitochondrial proteome and provide cardioprotective benefits to the diabetic heart.