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The induction of autophagy in the mammalian heart during the perinatal period is an essential adaptation required to survive early neonatal starvation; however, the mechanisms that mediate autophagy suppression once feeding is established are not known. Insulin signaling in the heart is transduced via insulin and IGF-1 receptors (IGF-1Rs). We disrupted insulin and IGF-1R signaling by generating mice with combined cardiomyocyte-specific deletion of Irs1 and Irs2. Here we show that loss of IRS signaling prevented the physiological suppression of autophagy that normally parallels the postnatal increase in circulating insulin. This resulted in unrestrained autophagy in cardiomyocytes, which contributed to myocyte loss, heart failure, and premature death. This process was ameliorated either by activation of mTOR with aa supplementation or by genetic suppression of autophagic activation. Loss of IRS1 and IRS2 signaling also increased apoptosis and precipitated mitochondrial dysfunction, which were not reduced when autophagic flux was normalized. Together, these data indicate that in addition to prosurvival signaling, insulin action in early life mediates the physiological postnatal suppression of autophagy, thereby linking nutrient sensing to postnatal cardiac development.

Ablating insulin receptors in cardiomyocytes causes subendocardial fibrosis and left ventricular (LV) dysfunction after 4 wk of transverse aortic constriction (TAC). To determine whether these maladaptive responses are precipitated by coronary vascular dysfunction, we studied mice with cardiomyocyte-restricted knock out of insulin receptors (CIRKO) and wild-type (WT) TAC mice before the onset of overt LV dysfunction. Two weeks of TAC produced comparable increases (P < 0.05 vs. respective sham) in heart weight/body weight (mg/g) in WT-TAC (8.03 ± 1.14, P < 0.05 vs. respective sham) and CIRKO-TAC (7.76 ± 1.25, P < 0.05 vs. respective sham) vs. WT-sham (5.64 ± 0.11) and CIRKO-sham (4.64 ± 0.10) mice. In addition, 2 wk of TAC were associated with similar LV geometry and function (echocardiography) and interstitial fibrosis (picrosirius red staining) in CIRKO and WT mice. Responses to acetylcholine (ACh), NG-monomethyl-l-arginine (l-NMMA), and sodium nitroprusside (SNP) were measured in coronary arteries that were precontracted to achieve ∼70% of maximal tension development using the thromboxane A2 receptor mimetic U-46619 (∼3 × 10-6 M). ACh-evoked vasorelaxation was absent in WT-TAC but was present in CIRKO-TAC albeit reduced relative to sham-operated animals. l-NMMA-evoked tension development was similar in vessels from CIRKO-TAC mice but was lower (P < 0.05) in WT-TAC animals vs. the respective sham-operated groups, and SNP-evoked vasorelaxation was similar among all mice. Thus estimates of stimulated and basal endothelial nitric oxide release were better preserved in CIRKO vs. WT mice in response to 2 wk of TAC. These findings indicate that maladaptive LV remodeling previously observed in CIRKO-TAC mice is not precipitated by coronary artery dysfunction, because CIRKO mice exhibit compensatory mechanisms (e.g., increased eNOS transcript and protein) to maintain coronary endothelial function in the setting of pressure overload. [ABSTRACT FROM AUTHOR]

Insulin resistance (IR) is associated with mitochondrial dysfunction: Whether mitochondrial dysfunction causes IR or is a consequence of IR is debated. To determine if impaired insulin signaling was sufficient to induce mitochondrial dysfunction, we used a mouse model (Ttr-Insr[sup -/-]) that lacks insulin receptors (IR) in all tissues, but is viable because of IR re-expression in the liver, β-cells and brain. We determined mitochondrial oxygen consumption and ATP production in permeabilized solens muscle incubated with 4mM succinate and 10µM rotenone from 12, 24 and 42-week-old Ttr-Insr[sup -/-]mice and age matched controls (WT) and measured expression levels of metabolic and mitochondrial genes by qPCR in the soleus muscles of 21 wk old Ttr-Insr[sup -/-] mice. Respiration rates, ATP production and ATP/oxygen (ATP/O) ratios in Ttr-Insr[sup -/-] were similar to control mice at 12 and 24 wks of age. However, significant mitochondrial dysfunction developed in 42 wk Ttr-Insr[sup -/-] relative to age-matched WT. Thus State 2 respiration of 42 wk old Ttr-Insr[sup -/-] mice were 5.2 ± 0.5 nmol O[sub 2]/min/mgdw versus 6.9 ± 0.5 in WT (p=0.02); State 3 respirations were 13.5 ± 1.0 in Ttr-Insr[sup -/-] versus 17.0 ± 0.7 in WT (p=0.02). State 4 respirations were similar in both groups but the respiratory control ratio (RC) which is the ratio of State 3/State 4, respiration was 2.1 ± 0.1 in Ttr-Insr[sup -/-] versus 2.7 ± 0.2 in WT, (p=0.01). ATP production rates were also reduced being 14.4 ± 2.1 nmol/min/mg/dw in Ttr-Insr[sup -/-] versus 25.5 ± 3 in WT (p=0.01) and ATP/O ratios were 1.0 ± 0.1 in the Ttr-Insr[sup -/-] versus 1.5 ± 0.2 in WT (p=0.06). There were no differences in expression levels of FAO and OXPHOS genes and their transcriptional regulators in 21-week-old Ttr-Insr[sup -/-] mice. Thus germ line IR deletion in skeletal muscle is not Sufficient to induce significant changes in skeletal muscle mitochondrial function or gene expression in younger mice, hut may predispose to age-related mitochondrial dysfunction. [ABSTRACT FROM AUTHOR]