Mild cognitive impairment and donepezil impact mitochondrial respiratory capacity in skeletal muscle

Alzheimer's Disease (ad) associates with insulin resistance and low aerobic capacity suggestive of impaired skeletal muscle mitochondrial function. However, direct measures of muscle mitochondrial function have not been performed in ad. This study (n = 50) compared skeletal muscle mitochondrial respiratory function and gene expression profiling in cognitively healthy older adults (CH; n = 24) to 26 individuals in the earliest phase of ad-related cognitive decline, mild cognitive impairment (MCI; n = 11) or MCI taking an ad medication, donepezil (MCI + med; n = 15). Mitochondrial respiratory kinetics were measured in permeabilized muscle fibers from skeletal muscle biopsies of the vastus lateralis. Untreated MCI subjects exhibited lower lipid-stimulated skeletal muscle mitochondrial respiration (State 3, ADP-stimulated) than both CH (P = 0.043) and MCI + med (P = 0.007) groups. MCI also exhibited poorer mitochondrial coupling control compared to CH (P = 0.014). RNA sequencing of skeletal muscle revealed unique differences in mitochondrial function and metabolism genes based on both MCI status (CH vs. MCI) and medication treatment (MCI vs. MCI + med). MCI + med modified over 600 skeletal muscle genes compared to MCI suggesting donepezeil powerfully impacts the transcriptional profile of skeletal muscle. Overall, skeletal muscle mitochondrial respiration is altered in untreated MCI but normalized in donepezil-treated MCI participants while mitochondrial leak control is impaired regardless of medication status. These results provide further evidence that skeletal muscle mitochondrial changes occur in the very early stages of ad, but is likely influenced by a common ad medicine. Further study of mitochondrial bioenergetics and the influence of transcriptional regulation in early ad is warranted.

A Leptin Receptor Antagonist Attenuates Adipose Tissue Browning and Muscle Wasting in Infantile Nephropathic Cystinosis-Associated Cachexia

Mice lacking the functional cystinosin gene (Ctns−/−), a model of infantile nephropathic cystinosis (INC), exhibit the cachexia phenotype with adipose tissue browning and muscle wasting. Elevated leptin signaling is an important cause of chronic kidney disease-associated cachexia. The pegylated leptin receptor antagonist (PLA) binds to but does not activate the leptin receptor. We tested the efficacy of this PLA in Ctns−/− mice. We treated 12-month-old Ctns−/− mice and control mice with PLA (7 mg/kg/day, IP) or saline as a vehicle for 28 days. PLA normalized food intake and weight gain, increased fat and lean mass, decreased metabolic rate and improved muscle function. It also attenuated perturbations of energy homeostasis in adipose tissue and muscle in Ctns−/− mice. PLA attenuated adipose tissue browning in Ctns−/− mice. PLA increased gastrocnemius weight and fiber size as well as attenuated muscle fat infiltration in Ctns−/− mice. This was accompanied by correcting the increased expression of muscle wasting signaling while promoting the decreased expression of myogenesis in gastrocnemius of Ctns−/− mice. PLA attenuated aberrant expressed muscle genes that have been associated with muscle atrophy, increased energy expenditure and lipolysis in Ctns−/− mice. Leptin antagonism may represent a viable therapeutic strategy for adipose tissue browning and muscle wasting in INC.

The role of IL-1 in adipose browning and muscle wasting in CKD-associated cachexia

Cytokines such as IL-6, TNF-α and IL-1β trigger inflammatory cascades which may play a role in the pathogenesis of chronic kidney disease (CKD)-associated cachexia. CKD was induced by 5/6 nephrectomy in mice. We studied energy homeostasis in Il1β−/−/CKD, Il6−/−/CKD and Tnfα−/−/CKD mice and compared with wild type (WT)/CKD controls. Parameters of cachexia phenotype were completely normalized in Il1β−/−/CKD mice but were only partially rescued in Il6−/−/CKD and Tnfα−/−/CKD mice. We tested the effects of anakinra, an IL-1 receptor antagonist, on CKD-associated cachexia. WT/CKD mice were treated with anakinra (2.5 mg/kg/day, IP) or saline for 6 weeks and compared with WT/Sham controls. Anakinra normalized food intake and weight gain, fat and lean mass content, metabolic rate and muscle function, and also attenuated molecular perturbations of energy homeostasis in adipose tissue and muscle in WT/CKD mice. Anakinra decreased serum and muscle expression of IL-6, TNF-α and IL-1β in WT/CKD mice. Anakinra attenuated browning of white adipose tissue in WT/CKD mice. Moreover, anakinra normalized gastrocnemius weight and fiber size as well as attenuated muscle fat infiltration in WT/CKD mice. This was accompanied by correcting the increased muscle wasting signaling pathways while promoting the decreased myogenesis process in gastrocnemius of WT/CKD mice. We performed qPCR analysis for the top 20 differentially expressed muscle genes previously identified via RNAseq analysis in WT/CKD mice versus controls. Importantly, 17 differentially expressed muscle genes were attenuated in anakinra treated WT/CKD mice. In conclusion, IL-1 receptor antagonism may represent a novel targeted treatment for adipose tissue browning and muscle wasting in CKD.

HIRA stabilizes skeletal muscle lineage identity

The epigenetic mechanisms coordinating the maintenance of adult cellular lineages and the inhibition of alternative cell fates remain poorly understood. Here we show that targeted ablation of the histone chaperone HIRA in myogenic cells leads to extensive transcriptional modifications, consistent with a role in maintaining skeletal muscle cellular identity. We demonstrate that conditional ablation of HIRA in muscle stem cells of adult mice compromises their capacity to regenerate and self-renew, leading to tissue repair failure. Chromatin analysis of Hira-deficient cells show a significant reduction of histone variant H3.3 deposition and H3K27ac modification at regulatory regions of muscle genes. Additionally, we find that genes from alternative lineages are ectopically expressed in Hira-mutant cells via MLL1/MLL2-mediated increase of H3K4me3 mark at silent promoter regions. Therefore, we conclude that HIRA sustains the chromatin landscape governing muscle cell lineage identity via incorporation of H3.3 at muscle gene regulatory regions, while preventing the expression of alternative lineage genes.

LncRNA-FKBP1C regulates muscle fiber type switching by affecting the stability of MYH1B

Long non-coding RNAs (lncRNAs) are well-known to participate in a variety of important regulatory processes in myogenesis. In our previous RNA-seq study (accession number GSE58755), we found that lncRNA-FKBP1C was differentially expressed between White Recessive Rock (WRR) and Xinghua (XH) chicken. Here, we have further demonstrated that lncRNA-FKBP1C interacted directly with MYH1B by biotinylated RNA pull-down assay and RNA immunoprecipitation (RIP). Protein stability and degradation experiments identified that lncRNA-FKBP1C enhanced the protein stability of MYH1B. Overexpression of lncRNA-FKBP1C inhibited myoblasts proliferation, promoted myoblasts differentiation, and participated in the formation of skeletal muscle fibers. LncRNA-FKBP1C could downregulate the fast muscle genes and upregulate slow muscle genes. Conversely, its interference promoted cell proliferation, repressed cell differentiation, and drove the transformation of slow-twitch muscle fibers to fast-twitch muscle fibers. Similar results were observed after knockdown of the MYH1B gene, but the difference was that the MYH1B gene had no effects on fast muscle fibers. In short, these data demonstrate that lncRNA-FKBP1C could bound with MYH1B and enhance its protein stability, thus affecting proliferation, differentiation of myoblasts and conversion of skeletal muscle fiber types.

The role of IL-1 in adipose browning and muscle wasting in CKD-associated cachexia

Cytokines such as IL-6, TNF-α and IL-1β trigger inflammatory cascades which may play a role in the pathogenesis of chronic kidney disease (CKD)-associated cachexia. CKD was induced by 5/6 nephrectomy in mice. We studied energy homeostasis in Il1β −/−/CKD, Il6−/−/CKD and Tnfα −/−/CKD mice and compared with wild type (WT)/CKD controls. Parameters of cachexia phenotype were completely normalized in Il1β −/−/CKD mice but were only partially rescued in Il6−/−/CKD and Tnfα −/−/CKD mice. We tested the effects of anakinra, an IL-1 receptor antagonist, on CKD-associated cachexia. WT/CKD mice were treated with anakinra (2.5 mg.kg.day, IP) or saline for 6 weeks and compared with WT/sham controls. Anakinra normalized food intake and weight gain, fat and lean mass content, metabolic rate and muscle function, and also attenuated molecular perturbations of energy homeostasis in adipose tissue and muscle in WT/CKD mice. Anakinra attenuated browning of white adipose tissue in WT/CKD mice. Moreover, anakinra normalized gastrocnemius weight and fiber size as well as attenuated muscle fat infiltration in WT/CKD mice. This was accompanied by correcting the increased muscle wasting signaling pathways while promoting the decreased myogenesis process in gastrocnemius of WT/CKD mice. We performed qPCR analysis for the top 20 differentially expressed muscle genes previously identified via RNAseq analysis in WT/CKD mice versus controls. Importantly, 17 differentially expressed muscle genes were attenuated in anakinra treated WT/CKD mice. In conclusion, IL-1 receptor antagonism may represent a novel targeted treatment for adipose tissue browning and muscle wasting in CKD.

The role of IL-1 in adipose browning and muscle wasting in CKD-associated cachexia

ABSTRACTCytokines such as IL-6, TNF-α and IL-1β trigger inflammatory cascades which may play a role in the pathogenesis of chronic kidney disease (CKD)-associated cachexia. CKD was induced by 5/6 nephrectomy in mice. We studied energy homeostasis in Il1β−/−/CKD, Il6−/−/CKD and Tnfα−/−/CKD mice and compared with wild type (WT)/CKD controls. Parameters of cachexia phenotype were completely normalized in Il1β−/−/CKD mice but were only partially rescued in Il6−/−/CKD and Tnfα−/−/CKD mice. We tested the effects of anakinra, an IL-1 receptor antagonist, on CKD-associated cachexia. WT/CKD mice were treated with anakinra (2.5 mg.kg.day, IP) or saline for 6 weeks and compared with WT/sham controls. Anakinra normalized food intake and weight gain, fat and lean mass content, metabolic rate and muscle function, and also attenuated molecular perturbations of energy homeostasis in adipose tissue and muscle in WT/CKD mice. Anakinra attenuated browning of white adipose tissue in WT/CKD mice. Moreover, anakinra normalized gastrocnemius weight and fiber size as well as attenuated muscle fat infiltration in WT/CKD mice. This was accompanied by correcting the increased muscle wasting signaling pathways while promoting the decreased myogenesis process in gastrocnemius of WT/CKD mice. We performed qPCR analysis for the top 20 differentially expressed muscle genes previously identified via RNAseq analysis in WT/CKD mice versus controls. Importantly, 17 differentially expressed muscle genes were attenuated in anakinra treated WT/CKD mice. In conclusion, IL-1 receptor antagonism may represent a novel targeted treatment for adipose tissue browning and muscle wasting in CKD.

Myogenin is required for assembly of the transcription machinery on muscle genes during skeletal muscle differentiation

Skeletal muscle gene expression is governed by the myogenic regulatory family (MRF) which includes MyoD (MYOD1) and myogenin (MYOG). MYOD1 and MYOG are known to regulate an overlapping set of muscle genes, but MYOD1 cannot compensate for the absence of MYOG in vivo. In vitro, late muscle genes have been shown to be bound by both factors, but require MYOG for activation. The molecular basis for this requirement was unclear. We show here that MYOG is required for the recruitment of TBP and RNAPII to muscle gene promoters, indicating that MYOG is essential in assembling the transcription machinery. Genes regulated by MYOD1 and MYOG include genes required for muscle fusion, myomaker and myomerger, and we show that myomaker is fully dependent on activation by MYOG. We also sought to determine the role of MYOD1 in MYOG dependent gene activation and unexpectedly found that MYOG is required to maintain Myod1 expression. However, we also found that exogenous MYOD1 was unable to compensate for the loss of Myog and activate muscle gene expression. Thus, our results show that MYOD1 and MYOG act in a feed forward loop to maintain each other’s expression and also show that it is MYOG, and not MYOD1, that is required to load TBP and activate gene expression on late muscle gene promoters bound by both factors.

Epigenetic regulation of Wnt7b expression by the cis-acting long noncoding RNA Lnc-Rewind in muscle stem cells

Skeletal muscle possesses an outstanding capacity to regenerate upon injury due to the adult muscle stem cell (MuSC) activity. This ability requires the proper balance between MuSC expansion and differentiation, which is critical for muscle homeostasis and contributes, if deregulated, to muscle diseases. Here, we functionally characterize a novel chromatin-associated long noncoding RNA (lncRNA), Lnc-Rewind, which is expressed in murine MuSCs and conserved in human. We find that, in mouse, Lnc-Rewind acts as an epigenetic regulator of MuSC proliferation and expansion by influencing the expression of skeletal muscle genes and several components of the WNT (Wingless-INT) signalling pathway. Among them, we identified the nearby Wnt7b gene as a direct Lnc-Rewind target. We show that Lnc-Rewind interacts with the G9a histone lysine methyltransferase and mediates the in cis repression of Wnt7b by H3K9me2 deposition. Overall, these findings provide novel insights into the epigenetic regulation of adult muscle stem cells fate by lncRNAs.

Effect of a Lower Limb Restless Period on Expression of Mir-1 and Mir-206 Neural Muscle Genes in Endurance Training Rats

Background and Aim: Several microRNAs are involved in regulating muscle mass, which plays an essential role in hypertrophy and atrophy of skeletal muscle, The present study examined the expression of some genes as regulators of muscular atrophy following a period of inertia in rats. Methods & Materials: For this purpose, 18 male Sprague-Dawley rats were divided into three groups (Control, Exercise+inactivity, and Inactivity). The exercise+inactivity group run on the treadmill for 18 weeks and five times per week. The hindlimb of the animal was immobilized for seven days with the casting method. Soleus muscle was extracted and the expression of the genes was measured by the RT-PCR method. Univariate ANOVA and Tukey post hoc test was used to determine the differences (α=0.05). Ethical Considerations: The Ethics Committee of the Tehran University of Medical Sciences Research approved this study (Code: IR.SUMS.REC.1396.S 463). Results: Results showed that immobilization in both Exercise+ inactivity and inactivity groups, compare to the control group, increased expression of miR-1 genes (P<0.10), FOXO3a (P<0.001) and decreased expression of miR-206 (P<0.007) and IGF-1 (P<0.001). This difference was statistically significant. Conclusion: According to the results of this study, it can be said that changes in the expression of RNAs by chromatography cause changes in the expression of muscle regulating genes, and although endurance exercises have protective effects, they cannot prevent these changes.