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Abstract Context Familial partial lipodystrophy (FPL), Dunnigan variety is characterized by skeletal muscle hypertrophy and insulin resistance besides fat loss from the extremities. The cause for the muscle hypertrophy and its functional consequences is not known. Objective To compare muscle strength and endurance, besides muscle protein synthesis rate between subjects with FPL and matched controls (n = 6 in each group). In addition, we studied skeletal muscle mitochondrial function and gene expression pattern to help understand the mechanisms for the observed differences. Methods Body composition by dual-energy X-ray absorptiometry, insulin sensitivity by minimal modelling, assessment of peak muscle strength and fatigue, skeletal muscle biopsy and calculation of muscle protein synthesis rate, mitochondrial respirometry, skeletal muscle transcriptome, proteome, and gene set enrichment analysis. Results Despite increased muscularity, FPL subjects did not demonstrate increased muscle strength but had earlier fatigue on chest press exercise. Decreased mitochondrial state 3 respiration in the presence of fatty acid substrate was noted, concurrent to elevated muscle lactate and decreased long-chain acylcarnitine. Based on gene transcriptome, there was significant downregulation of many critical metabolic pathways involved in mitochondrial biogenesis and function. Moreover, the overall pattern of gene expression was indicative of accelerated aging in FPL subjects. A lower muscle protein synthesis and downregulation of gene transcripts involved in muscle protein catabolism was observed. Conclusion Increased muscularity in FPL is not due to increased muscle protein synthesis and is likely due to reduced muscle protein degradation. Impaired mitochondrial function and altered gene expression likely explain the metabolic abnormalities and skeletal muscle dysfunction in FPL subjects.

INTRODUCTION Heart failure (HF) is characterized by reduced exercise capacity resulting from central and peripheral mechanisms. A primary peripheral mechanism is augmented neural feedback (via group III/IV afferents) arising from the locomotor muscles. This enhanced locomotor neural feedback may result from a variety of mechanisms including increased 1) metabo and/or mechanoreceptor expression, 2) metabolite production, and/or 3) mechano/metaboreceptor sensitivity. Previous studies have shown elevated expression of purinergic 2X3 (P2X3) and cyclooxygenase (COX‐2) in HF compared to sham animal models. However, it is unknown if metabo and/or mechanoreceptor (e.g., Piezo 1 and 2) expression are elevated in human HF. Further, it is unclear if altered receptor expression is related to the cardiovascular and ventilatory responses during exercise attributed to locomotor neural afferent feedback. The purpose of this study was to 1) determine if differences exist in the expression of skeletal muscle proteins associated with metabo/mechanoreflex activity between healthy individuals (CTL) and HF patients and 2) determine relationships between protein expression and the change in ventilatory and cardiovascular responses with locomotor muscle afferent inhibition during exercise. We hypothesized that 1) HF patients will demonstrate greater skeletal muscle protein expression associated with mechano/metaboreflex activity and 2) the increased protein expression will be associated with changes in ventilation, mean arterial pressure (MAP), and catecholamines during locomotor muscle afferent feedback inhibition in HF patients. METHODS In a randomized, placebo controlled cross‐over design, 10 CTL and 6 systolic HF (Age: 60±12 vs. 60±4 yrs, p=0.96; BMI: 26±3 vs. 31±5 kg/m 2 , p=0.01, respectively) patients completed cycling exercise at 60%VO 2 peak with lumbar intrathecal fentanyl or sham. Arterial blood pressure and catecholamines were measured via radial artery catheter during exercise. On a follow up visit, a muscle biopsy from the vastus lateralis was performed to isolate and measure COX‐2, P2X3, transient receptor potential vanilloid type 1 (TRPV1), Piezo 1, and Piezo 2 protein expression. RESULTS Protein expression of P2X3, COX‐2, and TRPV1 were greater in HF compared to CTL (all, p<0.05), with no difference between groups in Piezo 1 and 2 protein expression (p>0.05). HF compared to CTL had a greater decrease in ventilation with fentanyl compared to sham (−11±8 vs. −3±9%, p=0.04, respectively), with no difference between groups in MAP or norepinephrine (p>0.05). In HF, COX expression was negatively related to the change in ventilation (r= −0.87, p=0.02), MAP (r= −0.93, p<0.01), and norepinephrine (r= −0.85, p=0.03) with fentanyl. CONCLUSIONS These data demonstrate that metaborecptors (i.e. P2X3, COX‐2, and TRPV1) are elevated in HF compared to CTL. Furthermore, protein expression of COX‐2 was related to the cardiovascular and ventilatory changes observed with fentanyl in HF patients. These findings suggest that elevated expression of metaboreflex associated proteins contribute to the augmented locomotor muscle afferent feedback during exercise in HF. Support or Funding Information NHLBI RO1 HL126638 AHA 18POST3990251 This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .

Age‐related mitochondrial dysfunction is paralleled by reductions in gene transcripts and expression of proteins involved in cellular ATP production. Short‐term endurance exercise has been shown to enhance muscle protein synthesis in the elderly. We determined the impact of long‐term endurance exercise on gene expression and protein abundance of numerous proteins involved in cellular energetics. Vastus lateralis tissue was biopsied from 11 young sedentary (YS), 10 old sedentary (OS), 11 young trained (YT), and 11 old trained (OT) subjects. Trained subjects vigorously exercised ¡Ý 1 hr/d, ¡Ý five d/wk for ¡Ý 4 years. Large‐scale measurement of relative protein abundance was performed using isobaric tags for relative and absolute quantitation (iTRAQ) reagents and tandem mass spectrometry. Gene transcript levels were measured by high‐density oligonucleotide microarrays. Ingenuity Pathway Analysis was used to determine canonical pathways that were altered by age. Of the 33 proteins involved in cellular ATP production 27 were less abundant in OS vs. YS, while only 4 of these proteins were less abundant in OT vs. YT. Genes involved in glycolysis and oxidative phosphorylation were underexpressed in OS vs. YS, with no effects of age in OT vs. YT. CONCLUSIONS: Long‐term vigorous endurance exercise ameliorates the detrimental effects of old age on muscle gene and protein expression in humans.

Under some conditions, intracellular oxygen tension (PO2) may decrease to the point where oxygen availability limits respiration. Information about this critical PO2 and its determinants in vivo is sparse. PURPOSE: To determine the critical PO2 of human skeletal muscle, and its relationship to cellular energy consumption. METHODS: Interleaved proton and phosphorus magnetic resonance spectroscopy were used to quantify deoxymyoglobin and phosphorous metabolites in the tibialis anterior muscle of 6 subjects during 15 minutes of leg ischemia. Critical PO2 was determined as the PO2 at the phosphocreatine inflection point during ischemia. The rate of ATP consumption was determined from the linear slope of PCr depletion following the inflection point. RESULTS: The time to PCr inflection point was 282 ± 112 s (mean±SE). The corresponding critical PO2 was 0.47±0.27 torr, with a range of 0.21–0.96. PO2crit was not associated with the resting rate of ATP consumption (r =0.17), but was directly correlated to the rate of myoglobin desaturation (r =0.93) and inversely correlated to the time required to reach the PCr inflection point (r = −0.74). CONCLUSION: These data suggest that the relatively wide range of PO2crit in these subjects is attributable to inter‐subject differences in the ability of the muscle to maintain ATP production in the face of an ischemic insult. Support NIH AG21094, K02 AG023582

Aging is associated with altered mitochondrial physiology and exercise responsiveness in skeletal muscle. Activation of the unfolded protein response in the endoplasmic reticulum (UPR ER ) and mitochondria (UPR MT ) is linked with exercise‐induced adaptations in skeletal muscle, but the possibility that these processes impact exercise responsiveness and mitochondrial function in older humans has not been fully elucidated. The purpose of this study was to evaluate age‐related changes in UPR ER and UPR MT gene transcripts and protein abundance in response to a single bout of exercise. Muscle biopsies were obtained from 12 young (27±5 yr) and 12 older (75±5 yr) well‐matched, healthy men and women before exercise and 18h following a single bout of unilateral leg extension. Before exercise, a gene set enrichment analysis (GSEA) revealed that 27 genes associated with the UPR ER were upregulated in the older subjects compared to the young (enrichment false discovery rate [FDR] = 0.0842). After exercise, GSEA indicated upregulated UPR ER genes in both the young (FDR = 0.0405) and older subjects (FDR = 0.0619), however, pathway activation analysis revealed significantly greater activation of UPR ER and UPR MT gene transcripts post‐exercise in the younger subjects ( P < 0.05). In contrast, age did not affect key UPR‐regulatory protein abundance 18h post‐exercise. Interestingly, statistically significant correlations were observed in the young subjects between the mitochondrial transcriptional coactivator, peroxisome proliferator‐activated receptor gamma coactivator 1‐alpha (PGC‐1α) and key regulatory genes associated with the UPR ER (GRP78, R = 0.67; ATF6, R = 0.70) and the UPR MT (HSPE1, R = 0.61; HSPD1, R = 0.55; and HSPA9, R = 0.79), which were not evident in the older subjects. In conclusion, transcriptomic analysis revealed an age‐related decline in the adaptive UPR ER and UPR MT transcriptional response following a single bout of exercise that could potentially explain, in part, impaired exercise responsiveness and mitochondrial dysfunction with age. This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .

We recently demonstrated that high dietary fat (HFD) consumption results in a dramatic loss of myelinating cells and their progenitors in the adult CNS (Yoon et al., 2016). However, the mechanism(s) by which HFD drives dysmyelination are unknown. Since epidemiological studies indicate that metabolic syndrome is a key risk factor for multiple sclerosis (MS), a better understanding of how HFD contributes to oligodendrocyte loss and the capacity for myelin regeneration has the potential to highlight new treatment targets. In mice fed HFD, we found significant decreases in vertical activity by 4 wk and significant changes in ambulatory and stereotypy movements by 12 wk in the Open Field Test. HFD‐fed mice also spent less time in the center of the field as opposed to the perimeter, indicating an anxious phenotype. Mitochondrial isolated from the spinal cord of mice consuming HFD for 4 wk had significantly higher state 3 and state 4 respiration as determined by high‐resolution respirometry. However, by 12 wk, state 4 mitochondrial respiration was significantly less in the HFD group. Targeted LC‐LC‐mass spectroscopy approaches demonstrated that Citric Acid Cycle intermediates are also depleted in the spinal cord of mice consuming HFD for 12 wk compared to controls. Changes in genes related to mitochondrial morphology, quality control processes, and oxidative stress response were also found. In addition, there were significantly fewer Olig2+ cells and increased signs of lipid peroxidation products (4‐Hydroxynonenal‐immunoreactivity) in the corpus callosum of HFD consuming mice compared to those fed a regular diet. Supporting in vivo findings that oligodendrocytes are reduced in the spinal cord of mice consuming HFD, we observed increased mitochondrial fragmentation and a reduced oxygen consumption rate in oligodendrocyte precursors cultured with palmitic acid. Astrocytes however, significantly increased oxygen consumption following exposure to palmitic acid. Together, these findings suggest that changes in the adult spinal cord in response to HFD consumption creates an environment that is less conducive to neural repair by impacting mitochondria function and morphology and impairing oligodendrocyte function. To determine any impact of HFD on myelin regeneration, studies are ongoing to examine myelin regeneration using a murine model of Cuprizone‐mediated demyelination. Neurobehavioral assessments to date reveal significant interactions between HFD and myelin injury and repair. Understanding the cellular environment in response to dietary factors such as HFD consumption can help to guide care for individuals with MS and other conditions in which myelin loss plays a pathological role and has potential to identify new targets for intervention. This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .

Proton magnetic resonance spectroscopy was used to investigate the effect of ischemic contractions on human skeletal muscle oxygenation. PURPOSE: To determine if ischemia+contraction produces greater muscle deoxygenation than ischemia alone. METHODS: 5 men performed the following protocols in a 4 tesla magnet: P1) 10 min of ischemic rest, then 4 min of intermittent maximal isometric voluntary contractions (MVCs), and P2) 1 min of ischemic rest, then 3.4 min of intermittent MVCs and 5.6 min of ischemic recovery. Deoxymyoglobin (dMb) was normalized to the peak obtained during 10 min of ischemic rest. RESULTS: In P1, dMb reached a plateau during 10 min of ischemic rest and was not affected by contractions (102 ± 4.1%). In P2, dMb increased rapidly, followed by a plateau that tended to be lower than that obtained during ischemic rest (86.7 ± 2.32%, p = 0.063). During ischemic recovery, dMb gradually increased to the same level observed during resting ischemia (102 ± 4.2%). CONCLUSIONS: The addition of contractions after 10 min of ischemia does not result in further desaturation, suggesting that the muscle is already fully desaturated. Overall, these results validate the use of 10 min of resting ischemia to calibrate the dMb by MRS, and suggest that the observed plateaus in the dMb signal reflect inadequate oxygenation rather than mitochondrial inhibition by metabolite accumulation. Support NIH AG21094, K02 AG023582

The effects of different modes of exercise on mixed muscle protein synthesis (MMPS) in young (Y) and older (O) adults are not fully understood. We determined the effects of ET, RT, and CT on MMPS in 33Y (25±1y) and 31O (70±1y) adults who were randomized to one of three 8wk interventions: (i) Control: no exercise, (ii) ET: cycling 1h @ 65% VO 2 peak, 5x/wk, (iii) RT: RT 4x/wk. After completing the control period, the controls completed an 8wk (iv) CT program (ET & RT). Subjects were studied at baseline and 48h following the last training bout. [ 13 C 6 ]Phe was infused for 8h, with serial v. lateralis biopsies. Isotopic enrichments (IE) were measured by LC/MS for free Phe from tissue fluid (TF) and from that incorporated into MMP. MMPS (%/h) = (ΔIE MMP )/(IE TF )/t*100. A rank sum test was used to test baseline differences between Y and O. 2‐way ANCOVA was used to test for differences between groups by treatment, with baseline values serving as the covariate. MMPS (%/h) tended to be higher in Y (0.060±0.003) compared to O (0.053±0.003) (P=0.06). ET [57%, P<0.0001], RT [21%, P=0.042] and CT [42%, P<0.0001] increased MMPS independently of age (P>0.4). The ET‐induced increase in MMPS was greater than the RT‐induced increase (P<0.05), although ET unlike RT does not increase muscle mass suggesting that muscle protein turnover was increased. In conclusion, ET, RT and CT were effective at increasing MMPS independently of age. R01AG09531, KL2RR024151