Direct mitochondrial import of lactate supports resilient carbohydrate oxidation.

Lactate is the highest turnover circulating metabolite in mammals. While traditionally viewed as a waste product, lactate is an important energy source for many organs, but first must be oxidized to pyruvate for entry into the tricarboxylic acid cycle (TCA cycle). This reaction is thought to occur in the cytosol, with pyruvate subsequently transported into mitochondria via the mitochondrial pyruvate carrier (MPC). Using 13C stable isotope tracing, we demonstrated that lactate is oxidized in the myocardial tissue of mice even when the MPC is genetically deleted. This MPC-independent lactate import and mitochondrial oxidation is dependent upon the monocarboxylate transporter 1 (MCT1/Slc16a1). Mitochondria isolated from the myocardium without MCT1 exhibit a specific defect in mitochondrial lactate, but not pyruvate, metabolism. The import and subsequent mitochondrial oxidation of lactate by mitochondrial lactate dehydrogenase (LDH) acts as an electron shuttle, generating sufficient NADH to support respiration even when the TCA cycle is disrupted. In response to diverse cardiac insults, animals with hearts lacking MCT1 undergo rapid progression to heart failure with reduced ejection fraction. Thus, the mitochondrial import and oxidation of lactate enables carbohydrate entry into the TCA cycle to sustain cardiac energetics and maintain myocardial structure and function under stress conditions.

Clinical-transcriptional prioritization of the circulating proteome in human heart failure.

Given expanding studies in epidemiology and disease-oriented human studies offering hundreds of associations between the human "ome" and disease, prioritizing molecules relevant to disease mechanisms among this growing breadth is important. Here, we link the circulating proteome to human heart failure (HF) propensity (via echocardiographic phenotyping and clinical outcomes) across the lifespan, demonstrating key pathways of fibrosis, inflammation, metabolism, and hypertrophy. We observe a broad array of genes encoding proteins linked to HF phenotypes and outcomes in clinical populations dynamically expressed at a transcriptional level in human myocardium during HF and cardiac recovery (several in a cell-specific fashion). Many identified targets do not have wide precedent in large-scale genomic discovery or human studies, highlighting the complementary roles for proteomic and tissue transcriptomic discovery to focus epidemiological targets to those relevant in human myocardium for further interrogation.

Impact of Diabetes and Glycemia on Cardiac Improvement and Adverse Events Following Mechanical Circulatory Support.

BACKGROUND: Type 2 diabetes is prevalent in cardiovascular disease and contributes to excess morbidity and mortality. We sought to investigate the effect of glycemia on functional cardiac improvement, morbidity, and mortality in durable left ventricular assist device (LVAD) recipients. METHODS AND RESULTS: Consecutive patients with an LVAD were prospectively evaluated (n=531). After excluding patients missing pre-LVAD glycated hemoglobin (HbA1c) measurements or having inadequate post-LVAD follow-up, 375 patients were studied. To assess functional cardiac improvement, we used absolute left ventricular ejection fraction change (ΔLVEF: LVEF post-LVAD-LVEF pre-LVAD). We quantified the association of pre-LVAD HbA1c with ΔLVEF as the primary outcome, and all-cause mortality and LVAD-related adverse event rates (ischemic stroke/transient ischemic attack, intracerebral hemorrhage, gastrointestinal bleeding, LVAD-related infection, device thrombosis) as secondary outcomes. Last, we assessed HbA1c differences pre- and post-LVAD. Patients with type 2 diabetes were older, more likely men suffering ischemic cardiomyopathy, and had longer heart failure duration. Pre-LVAD HbA1c was inversely associated with ΔLVEF in patients with nonischemic cardiomyopathy but not in those with ischemic cardiomyopathy, after adjusting for age, sex, heart failure duration, and left ventricular end-diastolic diameter. Pre-LVAD HbA1c was not associated with all-cause mortality, but higher pre-LVAD HbA1c was shown to increase the risk of intracerebral hemorrhage, LVAD-related infection, and device thrombosis by 3 years on LVAD support (P<0.05 for all). HbA1c decreased from 6.68±1.52% pre-LVAD to 6.11±1.33% post-LVAD (P<0.001). CONCLUSIONS: Type 2 diabetes and pre-LVAD glycemia modify the potential for functional cardiac improvement and the risk for adverse events on LVAD support. The degree and duration of pre-LVAD glycemic control optimization to favorably affect these outcomes warrants further investigation.

Enhancing mitochondrial pyruvate metabolism ameliorates ischemic reperfusion injury in the heart.

The clinical therapy for treating acute myocardial infarction is primary percutaneous coronary intervention (PPCI). PPCI is effective at reperfusing the heart; however, the rapid reintroduction of blood can cause ischemia-reperfusion (I/R). Reperfusion injury is responsible for up to half of the total myocardial damage, but there are no pharmacological interventions to reduce I/R. We previously demonstrated that inhibiting monocarboxylate transporter 4 (MCT4) and redirecting pyruvate toward oxidation can blunt hypertrophy. We hypothesized that this pathway might be important during I/R. Here, we establish that the pyruvate-lactate axis plays a role in determining myocardial salvage following injury. After I/R, the mitochondrial pyruvate carrier (MPC), required for pyruvate oxidation, is upregulated in the surviving myocardium. In cardiomyocytes lacking the MPC, there was increased cell death and less salvage after I/R, which was associated with an upregulation of MCT4. To determine the importance of pyruvate oxidation, we inhibited MCT4 with a small-molecule drug (VB124) at reperfusion. This strategy normalized reactive oxygen species (ROS), mitochondrial membrane potential (ΔΨ), and Ca2+, increased pyruvate entry to the TCA cycle, increased oxygen consumption, and improved myocardial salvage and functional outcomes following I/R. Our data suggest normalizing pyruvate-lactate metabolism by inhibiting MCT4 is a promising therapy to mitigate I/R injury.

Integrating molecular and clinical variables to predict myocardial recovery.

Mechanical unloading and circulatory support with left ventricular assist devices (LVADs) mediate significant myocardial improvement in a subset of advanced heart failure (HF) patients. The clinical and biological phenomena associated with cardiac recovery are under intensive investigation. Left ventricular (LV) apical tissue, alongside clinical data, were collected from HF patients at the time of LVAD implantation (n=208). RNA was isolated and mRNA transcripts were identified through RNA sequencing and confirmed with RT-qPCR. To our knowledge this is the first study to combine transcriptomic and clinical data to derive predictors of myocardial recovery. We used a bioinformatic approach to integrate 59 clinical variables and 22,373 mRNA transcripts at the time of LVAD implantation for the prediction of post-LVAD myocardial recovery defined as LV ejection fraction (LVEF) ≥40% and LV end-diastolic diameter (LVEDD) ≤5.9cm, as well as functional and structural LV improvement independently by using LVEF and LVEDD as continuous variables, respectively. To substantiate the predicted variables, we used a multi-model approach with logistic and linear regressions. Combining RNA and clinical data resulted in a gradient boosted model with 80 features achieving an AUC of 0.731±0.15 for predicting myocardial recovery. Variables associated with myocardial recovery from a clinical standpoint included HF duration, pre-LVAD LVEF, LVEDD, and HF pharmacologic therapy, and LRRN4CL (ligand binding and programmed cell death) from a biological standpoint. Our findings could have diagnostic, prognostic, and therapeutic implications for advanced HF patients, and inform the care of the broader HF population.

Enhancing mitochondrial pyruvate metabolism ameliorates myocardial ischemic reperfusion injury.

The established clinical therapy for the treatment of acute myocardial infarction is primary percutaneous coronary intervention (PPCI) to restore blood flow to the ischemic myocardium. PPCI is effective at reperfusing the ischemic myocardium, however the rapid re-introduction of oxygenated blood also can cause ischemia-reperfusion (I/R) injury. Reperfusion injury is the culprit for up to half of the final myocardial damage, but there are no clinical interventions to reduce I/R injury. We previously demonstrated that inhibiting the lactate exporter, monocarboxylate transporter 4 (MCT4), and re-directing pyruvate towards oxidation can blunt isoproterenol-induced hypertrophy. Based on this finding, we hypothesized that the same pathway might be important during I/R. Here, we establish that the pyruvate-lactate metabolic axis plays a critical role in determining myocardial salvage following injury. Post-I/R injury, the mitochondrial pyruvate carrier (MPC), required for pyruvate oxidation, is upregulated in the surviving myocardium following I/R injury. MPC loss in cardiomyocytes caused more cell death with less myocardial salvage, which was associated with an upregulation of MCT4 in the myocardium at risk of injury. We deployed a pharmacological strategy of MCT4 inhibition with a highly selective compound (VB124) at the time of reperfusion. This strategy normalized reactive oxygen species (ROS), mitochondrial membrane potential (Δψ), and Ca 2+ , increased pyruvate entry to TCA cycle, and improved myocardial salvage and functional outcomes following I/R injury. Altogether, our data suggest that normalizing the pyruvate-lactate metabolic axis via MCT4 inhibition is a promising pharmacological strategy to mitigate I/R injury.

Hypoxia Attenuates Pressure Overload-Induced Heart Failure.

BACKGROUND: Alveolar hypoxia is protective in the context of cardiovascular and ischemic heart disease; however, the underlying mechanisms are incompletely understood. The present study sought to test the hypothesis that hypoxia is cardioprotective in left ventricular pressure overload (LVPO)-induced heart failure. We furthermore aimed to test that overlapping mechanisms promote cardiac recovery in heart failure patients following left ventricular assist device-mediated mechanical unloading and circulatory support. METHODS AND RESULTS: We established a novel murine model of combined chronic alveolar hypoxia and LVPO following transverse aortic constriction (HxTAC). The HxTAC model is resistant to cardiac hypertrophy and the development of heart failure. The cardioprotective mechanisms identified in our HxTAC model include increased activation of HIF (hypoxia-inducible factor)-1α-mediated angiogenesis, attenuated induction of genes associated with pathological remodeling, and preserved metabolic gene expression as identified by RNA sequencing. Furthermore, LVPO decreased Tbx5 and increased Hsd11b1 mRNA expression under normoxic conditions, which was attenuated under hypoxic conditions and may induce additional hypoxia-mediated cardioprotective effects. Analysis of samples from patients with advanced heart failure that demonstrated left ventricular assist device-mediated myocardial recovery revealed a similar expression pattern for TBX5 and HSD11B1 as observed in HxTAC hearts. CONCLUSIONS: Hypoxia attenuates LVPO-induced heart failure. Cardioprotective pathways identified in the HxTAC model might also contribute to cardiac recovery following left ventricular assist device support. These data highlight the potential of our novel HxTAC model to identify hypoxia-mediated cardioprotective mechanisms and therapeutic targets that attenuate LVPO-induced heart failure and mediate cardiac recovery following mechanical circulatory support.

Postnatal growth restriction alters myocardial mitochondrial energetics in mice.

Postnatal growth restriction (PGR) can increase the risk of cardiovascular disease (CVD) potentially due to impairments in oxidative phosphorylation (OxPhos) within cardiomyocyte mitochondria. The purpose of this investigation was to determine if PGR impairs cardiac metabolism, specifically OxPhos. FVB (Friend Virus B-type) mice were fed a normal-protein (NP: 20% protein), or low-protein (LP: 8% protein) isocaloric diet 2 weeks before mating. LP dams produce ∼20% less milk, and pups nursed by LP dams experience reduced growth into adulthood as compared to pups nursed by NP dams. At birth (PN1), pups born to dams fed the NP diet were transferred to LP dams (PGR group) or a different NP dam (control group: CON). At weaning (PN21), all mice were fed the NP diet. At PN22 and PN80, mitochondria were isolated for respirometry (oxygen consumption rate, J O 2 ${J_{{{\mathrm{O}}_{\mathrm{2}}}}}$ ) and fluorimetry (reactive oxygen species emission, J H 2 O 2 ${J_{{{\mathrm{H}}_{\mathrm{2}}}{{\mathrm{O}}_{\mathrm{2}}}}}$ ) analysis measured as baseline respiration (LEAK) and with saturating ADP (OxPhos). Western blotting at PN22 and PN80 determined protein abundance of uncoupling protein 3, peroxiredoxin-6, voltage-dependent anion channel and adenine nucleotide translocator 1 to provide further insight into mitochondrial function. ANOVAs with the main effects of diet, sex and age with α-level of 0.05 was set a priori. Overall, PGR (7.8 ± 1.1) had significant (P = 0.01) reductions in respiratory control in complex I when compared to CON (8.9 ± 1.0). In general, our results show that PGR led to higher electron leakage in the form of free radical production and reactive oxygen species emission. No significant diet effects were found in protein abundance. The observed reduced respiratory control and increased ROS emission in PGR mice may increase risk for CVD in mice.

The Effect of Downhill Running on Quadriceps Muscle in Growth-Restricted Mice.

INTRODUCTION: Growth restriction (GR) reduces ribosome abundance and skeletal muscle mass in mice. A reduction in skeletal muscle mass increases the risk of frailty and is associated with high morbidity and mortality rates. As eccentric type exercise increases muscle mass, this investigation aimed to determine if eccentric loading of skeletal muscle via downhill running (DHR) increased muscle mass in GR mice. METHODS: Mice were growth-restricted either gestational undernutrition (GUN, n = 8 litters), postnatal undernutrition (PUN, n = 8 litters), or were not restricted (CON, n = 8 litters) via a validated cross-fostering nutritive model. On postnatal day (PN) 21, all mice were weaned to a healthy diet, isolating the period of GR to early life as seen in humans. At PN45, mice were assigned to either a DHR (CON, n = 4 litters; GUN, n = 4 litters; PUN, n = 4 litters) or sedentary (SED: CON, n = 4 litters; GUN, n = 4 litters; PUN, n = 4 litters) group. Downhill running (16% decline: 18 m·min -1 ) was performed in 30-min bouts, three times per week, for 12 wk on a rodent treadmill. At PN129, the quadriceps femoris was dissected and evaluated for mass, myofiber size and type, and molecular markers of growth. RESULTS: Following training, CON-DHR mice having larger cells than CON-SED, GUN-SED, PUN-SED, and PUN-DHR mice ( P < 0.05). The PUN group (as compared with CON) had reduced body mass ( P < 0.001), upstream binding factor abundance ( P = 0.012), phosphor-mTOR ( P < 0.001), and quadriceps mass ( P = 0.02). The GUN and PUN groups had increased MuRF1 abundance ( P < 0.001) compared with CON ( P < 0.001). CONCLUSIONS: The blunted response to training suggests GR mice may have anabolic resistance when exposed to eccentric type exercise.

The RNA editor ADAR2 promotes immune cell trafficking by enhancing endothelial responses to interleukin-6 during sterile inflammation.

Immune cell trafficking constitutes a fundamental component of immunological response to tissue injury, but the contribution of intrinsic RNA nucleotide modifications to this response remains elusive. We report that RNA editor ADAR2 exerts a tissue- and stress-specific regulation of endothelial responses to interleukin-6 (IL-6), which tightly controls leukocyte trafficking in IL-6-inflamed and ischemic tissues. Genetic ablation of ADAR2 from vascular endothelial cells diminished myeloid cell rolling and adhesion on vascular walls and reduced immune cell infiltration within ischemic tissues. ADAR2 was required in the endothelium for the expression of the IL-6 receptor subunit, IL-6 signal transducer (IL6ST; gp130), and subsequently, for IL-6 trans-signaling responses. ADAR2-induced adenosine-to-inosine RNA editing suppressed the Drosha-dependent primary microRNA processing, thereby overwriting the default endothelial transcriptional program to safeguard gp130 expression. This work demonstrates a role for ADAR2 epitranscriptional activity as a checkpoint in IL-6 trans-signaling and immune cell trafficking to sites of tissue injury.

Longitudinal effects of growth restriction on the murine gut microbiome and metabolome.

Undernutrition-induced growth restriction in the early stages of life increases the risk of chronic disease in adulthood. Although metabolic impairments have been observed, few studies have characterized the gut microbiome and gut-liver metabolome profiles of growth-restricted animals during early-to-mid-life development. To induce growth restriction, mouse offspring were either born to gestational undernutrition (GUN) or suckled from postnatal undernutrition (PUN) dams fed a protein-restricted diet (8% protein) or control diet (CON; 20% protein) until weaning at postnatal age of 21 days (PN21). At PN21, all mice were fed the CON diet until adulthood (PN80). Livers were collected at PN21 and PN80, and fecal samples were collected weekly starting at PN21 (postweaning week 1) until PN80 (postweaning week 5) for gut microbiome and metabolome analyses. PUN mice exhibited the most alterations in gut microbiome and gut and liver metabolome compared with CON mice. These mice had altered fecal microbial ß-diversity (P = 0.001) and exhibited higher proportions of Bifidobacteriales [linear mixed model (LMM) P = 7.1 × 10-6), Clostridiales (P = 1.459 × 10-5), Erysipelotrichales (P = 0.0003), and lower Bacteroidales (P = 4.1 × 10-5)]. PUN liver and fecal metabolome had a reduced total bile acid pool (P < 0.01), as well as lower abundance of riboflavin (P = 0.003), amino acids [i.e., methionine (P = 0.0018), phenylalanine (P = 0.0015), and tyrosine (P = 0.0041)], and higher excreted total peptides (LMM P = 0.0064) compared with CON. Overall, protein restriction during lactation permanently alters the gut microbiome into adulthood. Although the liver bile acids, amino acids, and acyl-carnitines recovered, the fecal peptides and microbiome remained permanently altered into adulthood, indicating that inadequate protein intake in a specific time frame in early life can have an irreversible impact on the microbiome and fecal metabolome.NEW & NOTEWORTHY Undernutrition-induced early-life growth restriction not only leads to increased disease risk but also permanently alters the gut microbiome and gut-liver metabolome during specific windows of early-life development.

Etiology-Specific Remodeling in Ventricular Tissue of Heart Failure Patients and Its Implications for Computational Modeling of Electrical Conduction.

With an estimated 64.3 million cases worldwide, heart failure (HF) imposes an enormous burden on healthcare systems. Sudden death from arrhythmia is the major cause of mortality in HF patients. Computational modeling of the failing heart provides insights into mechanisms of arrhythmogenesis, risk stratification of patients, and clinical treatment. However, the lack of a clinically informed approach to model cardiac tissues in HF hinders progress in developing patient-specific strategies. Here, we provide a microscopy-based foundation for modeling conduction in HF tissues. We acquired 2D images of left ventricular tissues from HF patients (n = 16) and donors (n = 5). The composition and heterogeneity of fibrosis were quantified at a sub-micrometer resolution over an area of 1 mm2. From the images, we constructed computational bidomain models of tissue electrophysiology. We computed local upstroke velocities of the membrane voltage and anisotropic conduction velocities (CV). The non-myocyte volume fraction was higher in HF than donors (39.68 ± 14.23 vs. 22.09 ± 2.72%, p < 0.01), and higher in ischemic (IC) than nonischemic (NIC) cardiomyopathy (47.2 ± 16.18 vs. 32.16 ± 6.55%, p < 0.05). The heterogeneity of fibrosis within each subject was highest for IC (27.1 ± 6.03%) and lowest for donors (7.47 ± 1.37%) with NIC (15.69 ± 5.76%) in between. K-means clustering of this heterogeneity discriminated IC and NIC with an accuracy of 81.25%. The heterogeneity in CV increased from donor to NIC to IC tissues. CV decreased with increasing fibrosis for longitudinal (R 2 = 0.28, p < 0.05) and transverse conduction (R 2 = 0.46, p < 0.01). The tilt angle of the CV vectors increased 2.1° for longitudinal and 0.91° for transverse conduction per 1% increase in fibrosis. Our study suggests that conduction fundamentally differs in the two etiologies due to the characteristics of fibrosis. Our study highlights the importance of the etiology-specific modeling of HF tissues and integration of medical history into electrophysiology models for personalized risk stratification and treatment planning.

Physical Activity Engagement Worsens Health Outcomes and Limits Exercise Capacity in Growth-restricted Mice.

INTRODUCTION: A total of 161 million children a year are growth restricted, leading to a 47% increased risk of chronic disease in adulthood. Physical activity (PA) reduces the risk of mortality from chronic disease. The purpose of the present investigation was to determine the effect of a PA intervention (wheel running) on cardiac and skeletal muscle capacities in gestational (GUN) and postnatal (PUN) growth-restricted mice as compared with nonrestricted controls (CON). METHODS: A low-protein cross-fostering FVB mouse model was used to induce growth restriction during gestation and the first 21 d of postnatal life. Mouse pups were recovered on a healthy diet until mature and provided wheel access for 3 wk. At completion of the PA intervention, mice underwent maximal exercise testing on a treadmill, echocardiography, and skeletal muscle histology. RESULTS: After the PA intervention, CON mice had a 45% improvement in maximal exercise capacity (P = 0.0390) because of cardiac and skeletal muscle adaptations, but GUN and PUN mice did not. Alarmingly, PUN female mice exposed to wheels had 11.45% lower left ventricular volume (P = 0.0540) and 18% lower left ventricle area (P = 0.0585), with blood flow velocities indicative of cardiac fibrosis (GUN had elevated isovolumetric contraction time P = 0.0374; GUN females and PUN males had longer isovolumetric relaxation time P = 0.0703). PUN male mice had mixed skeletal muscle responses with an oxidative shift in the diaphragm (P = 0.0162) but a glycolytic shift in the extensor digitorum longus (P = 0.0647). PUN female mice had a glycolytic shift in the soleus after wheel running. CONCLUSIONS: Unexpectedly, growth-restricted mice were nonresponders to a PA intervention and displayed negative cardiac outcomes.

Postnatal Growth Restriction in Mice Alters Cardiac Protein Composition and Leads to Functional Impairment in Adulthood.

Postnatal growth restriction (PGR) increases the risk for cardiovascular disease (CVD) in adulthood, yet there is minimal mechanistic rationale for the observed pathology. The purpose of this study was to identify proteomic differences in hearts of growth-restricted and unrestricted mice, and propose mechanisms related to impairment in adulthood. Friend leukemia virus B (FVB) mouse dams were fed a control (CON: 20% protein), or low-protein (LP: 8% protein) isocaloric diet 2 weeks before mating. LP dams produce 20% less milk, inducing growth restriction. At birth (postnatal; PN1), pups born to dams fed the CON diet were switched to LP dams (PGR group) or a different CON dam. At PN21, a sub-cohort of CON (n = 3 males; n = 3 females) and PGR (n = 3 males; n = 3 females) were euthanized and their proteome analyzed by two-dimensional differential in-gel electrophoresis (2D DIGE) and mass spectroscopy. Western blotting and silver nitrate staining confirmed 2D DIGE results. Littermates (CON: n = 4 males and n = 4 females; PGR: n = 4 males and n = 4 females) were weaned to the CON diet. At PN77, echocardiography measured cardiac function. At PN80, hearts were removed for western blotting to determine if differences persisted into adulthood. 2D DIGE and western blot confirmation indicated PGR had reductions in p57kip2, Titin (Ttn), and Collagen (Col). At PN77, PGR had impaired cardiac function as measured by echocardiography. At PN80, western blots of p57kip2 showed protein abundance recovered from PN21. PN80 silver staining of large molecular weight proteins (Ttn and Col) was reduced in PGR. PGR reduces cell cycle activity at PN21, which is recovered in adulthood. However, collagen fiber networks are altered into adulthood.

Infant blood lipids: a systematic review of predictive value and influential factors.

INTRODUCTION: Blood lipid screening recommendations begin at ages 9-11 years, despite poor adherence and evidence of fatty streaks in coronary arteries by 3 years of age. For cardiovascular disease (CVD) prevention, there may be value in earlier measurement of blood lipids. AREAS COVERED: The present systematic review examines evidence concerning total cholesterol, low-density lipoprotein, high-density lipoprotein, and triglycerides during the infant period. Included are studies examining the extent to which infant blood lipids predict later values in childhood and factors that influence their magnitude. A total of 38 articles (published from 1965 to 2013) met inclusion criteria and were examined in this review. EXPERT OPINION: Longitudinal data suggest correlative relationships in all lipid values around 6 months of age, except for TRG. Influential factors related to blood lipids in infancy include sex, race, family history, feeding, gestational length, birth weight, and maternal factors. Clinical measurement of infant lipids could perhaps provide an early marker of CVD and a target of early CVD prevention strategies. The identification of personal characteristics that associate with high or low values in each lipid could become important in the early identification of vulnerable populations and the promotion of personalized CVD prevention.

Early life undernutrition reduces maximum treadmill running capacity in adulthood in mice.

Undernutrition during early life causes chronic disease with specific impairments to the heart and skeletal muscle. The purpose of this study was to determine the effects of early life undernutrition on adult exercise capacity as a result of cardiac and skeletal muscle function. Pups were undernourished during gestation (GUN) or lactation (PUN) using a cross-fostering nutritive mouse model. At postnatal day 21, all mice were weaned and refed a control diet. At postnatal day 67, mice performed a maximal treadmill test. Echocardiography and Doppler blood flow analysis was performed at postnatal day 72, following which skeletal muscle cross-sectional area (CSA) and fiber type were determined. Maximal running capacity was reduced (diet: P = 0.0002) in GUN and PUN mice. Left ventricular mass (diet: P = 0.03) and posterior wall thickness during systole (diet × sex: P = 0.03) of GUN and PUN mice was reduced, causing PUN mice to have reduced (diet: P = 0.04) stroke volume. Heart rate of GUN mice showed a trend (diet: P = 0.07) towards greater resting values than other groups. PUN mice had greater CSA of soleus fibers. PUN had a reduced (diet: P = 0.03) proportion of type-IIX fibers in the extensor digitorum longus (EDL) and a greater (diet: P = 0.008) percentage of type-IIB fibers in the EDL. In conclusion, gestational and postnatal undernourishment impairs exercise capacity.

The Effect of Growth Restriction on Voluntary Physical Activity Engagement in Mice.

INTRODUCTION: The purpose of this study was to determine the effect of growth restriction on the biological regulation of physical activity. METHODS: Using a cross-fostering, protein-restricted nutritive model, mice were growth-restricted during either gestation (GUN; N = 3 litters) or postnatal life (PUN; N = 3 litters). At 21 d of age, all mice pups were weaned and fed a nonrestrictive healthy diet for the remainder of the study. At 45 d of age, mice were individually housed in cages with free moving running wheels to assess physical activity engagement. At day 70, mice were euthanized, and the nucleus accumbens was analyzed for dopamine receptor 1 expression. Skeletal muscle fiber type and cross-sectional area of the soleus, extensor digitorom longus, and diaphragm were analyzed by immunohistochemistry. The soleus from the other hindleg was evaluated for calsequestrin 1 and annexin A6 expression. RESULTS: The PUN female mice (15,365 ± 8844 revolutions per day) had a reduction (P = 0.0221) in wheel revolutions per day as compared with the GUN (38,667 ± 8648 revolutions per day) and CON females (36,421.0 ± 6700 revolutions per day). The PUN female mice also expressed significantly higher dopamine receptor 1 compared (P = 0.0247) to the other groups. The PUN female soleus had a higher expression of calsequestrin 1, along with more type IIb fibers (P = 0.0398). CONCLUSIONS: Growth restriction during lactation reduced physical activity in female mice by reducing the central drive to be active and displayed a more fatigable skeletal muscle phenotype.