IGF-II-mediated downregulation of peroxisome proliferator-activated receptor-γ coactivator-1α in myoblast cells involves PI3K/Akt/FoxO1 signaling pathway

Differential expression of microRNAs in serum exosomes of obese and non-obese mice and analysis of their function

OBJECTIVE

To extract exosomes from obese and non-obese mice, screen specifically expressed microRNAs by high-throughput sequencing and explore their roles.

METHODS

An animal obesity model was constructed, and the successful construction of the obesity model was verified by HE staining, Western Blot and RT-qPCR. In addition, exosomes were extracted and verified by Western Blot. High-throughput sequencing was performed on the extracted serum exosomes to screen for differentially expressed microRNAs. fluorescence quantitative RT-PCR (RT-qPCR) was used to validate the differentially expressed miRNAs and explore their functions.

RESULTS

8 microRNAs were up-regulated and 11 microRNAs were down-regulated. mmu-miR-674-5p and X_28316 were significantly down-regulated and had the greatest impact on protein pathways. 8_13258 was significantly up-regulated and affected multiple protein pathways. GO enrichment analysis suggested that the differentially expressed microRNAs were mainly involved in the cleavage of microtubule activity, transferase activity/transferase pentameric acid. GO enrichment analysis suggested that differentially expressed microRNAs were mainly involved in the processes of cleavage microtubule activity, transferase activity/transfer pentamer, and threonine phosphatase/threonine kinase activity.KEGG pathway enrichment analysis showed that differentially expressed microRNAs were mainly involved in the processes of regulating the phosphorylation of TP53 activity, the G2/M DNA damage checkpoint, and the processing of the ends of DNA double-strand breaks. Protein interaction networks were enriched for Stat3, Fgr, Camk2b, Rac1, Asb6, and Ankfy1. Suggesting that they may be mediated by differential genes to participate in the process of insulin resistance. qRT-PCR results showed that the expression trend of mmu-miR-674-5p was consistent with the sequencing results. It suggests that it may be able to participate in the regulation of insulin resistance as a target gene.

CONCLUSION

microRNAs were differentially expressed in serum exosomes of obese and non-obese mice and might be involved in the specific regulation of insulin resistance. mmu-miR-674-5p was differentially expressed significantly and the validation trend was consistent with it, suggesting that it might be able to participate in the regulation of insulin resistance as a target gene.

FHL3 gene regulates bovine skeletal muscle cell growth through the PI3K/Akt/mTOR signaling pathway

Beef quality is a critical factor in evaluating the effectiveness of beef cattle production. Fiber types play key roles in determining muscle growth and meat quality characteristics. FHL3 is de novo expressed in skeletal muscle and is responsible for MyHC isoform expression in C2C12 cells. Nevertheless, the precise function of this factor in regulating the proliferation, differentiation, and fiber type of bovine skeletal muscle cells (BSMCs) have yet to be identified. This study aimed to investigate the impact of the FHL3 on BSMCs proliferation, differentiation, and muscle fiber types. The results revealed that the FHL3 promoted BSMCs proliferation, inhibited differentiation, increased type II muscle fiber expression, and decreased type I muscle fiber expression. Meanwhile, the FHL3 promoted the expression and phosphorylation levels of PI3K, Akt, and mTOR in the PI3K/Akt/mTOR signaling pathway, and inhibited the expression and phosphorylation levels of PI3K, Akt, and mTOR after treatment with the pathway inhibitor LY294002, furthermore, it promoted differentiation and inhibited proliferation of BSMCs, while promoting the expression of type II muscle fibers and inhibiting the expression of type I muscle fibers. The results suggest that the FHL3 has an effect on promoting the proliferation and inhibiting the differentiation of BSMCs through the PI3K/Akt/mTOR signaling pathway, but the effect of the FHL3 on myofiber type conversion is not regulated by this pathway. The objective of this study is to enhance our understanding of the molecular function of FHL3 in the development of BSMCs.

IGF-1 knockdown inhibits phosphorylation of Akt and ERK in chicken embryonic myotubes

OBJECTIVE

We examined whether auto/paracrine insulin-like growth factor-1 (IGF-1) contributes to the phosphorylation of Akt and ERK in chicken myotubes.

METHODS

Chicken myotubes were treated with IGF-1 siRNA, and then total RNA and protein were harvested for real-time PCR and western blot analysis.

RESULTS

Treatment with IGF-1 siRNA inhibited the phosphorylation of Akt and ERK, but not of ribosomal protein S6, in chicken myotubes. Interestingly, IGF-1 siRNA downregulated the expression of IGF-2.

CONCLUSIONS

The results of this study suggest that auto/paracrine IGF-1 contributes to Akt and ERK phosphorylation in chicken myotubes.

Sirt6 opposes glycochenodeoxycholate-induced apoptosis of biliary epithelial cells through the AMPK/PGC-1α pathway

Background

Induction of biliary epithelial cell apoptosis by toxic bile acids is involved in the development of cholestatic disease, but the underlying molecular mechanism is not clear. The purpose of this study was to investigate the molecular mechanisms involved in Sirt6 protection against the apoptosis of human intrahepatic biliary epithelial cells (HiBEC) induced by the bile acid glycochenodeoxycholate (GCDC).

Results

Sirt6 was either overexpressed or knocked down in HiBEC, with or without GCDC pretreatment. The CCK-8 assay was used to assess cell viability and, Hoechst 33258 staining was used to determine apoptotic rate. Mitochondrial DNA (mtDNA) copy number, malondialdehyde (MDA) and reactive oxygen species (ROS) production were detected to evaluate the severity of the mitochondrial dysfunction and oxidative stress. The mRNA and protein levels of PGC-1α, Nrf1, and Nrf2 were analyzed using RT-qPCR and western blot assay. The results showed that Sirt6 opposed GCDC-induced apoptosis in HiBEC via up-regulating PGC-1α expression and stabilizing mtDNA. We used agonists and inhibitors of AMPK to demonstrate that Sirt6 increased PGC-1α expression through the AMPK pathway whereas GCDC had the opposite effect. Finally, western blot, luciferase assay, and co-immunoprecipitation were used to describe a direct interaction and acetylation modification of PGC-1α by Sirt6.

Conclusion

Our data illuminated that Sirt6 ameliorated GCDC-induced HiBEC apoptosis by upregulating PGC-1α expression through the AMPK pathway and its deacetylation effect.

FOXO1 inhibition prevents renal ischemia-reperfusion injury via cAMP-response element binding protein/PPAR-γ coactivator-1α-mediated mitochondrial biogenesis

BACKGROUND AND PURPOSE

Growing evidence indicates targeting mitochondrial dynamics and biogenesis could accelerate recovery from renal ischemia-reperfusion (I/R) injury, but the underlying mechanisms remain elusive. Transcription factor forkhead box O1 (FOXO1) is a key regulator of mitochondrial homeostasis and plays a pathological role in the progression of renal disease.

EXPERIMENTAL APPROACH

A mouse model of renal I/R injury and a hypoxia/reoxygenation (H/R) injury model for human renal tubular epithelial cells were used.

KEY RESULTS

I/R injury up-regulated renal expression of FOXO1 and treatment with FOXO1-selective inhibitor AS1842856 prior to I/R injury decreased serum urea nitrogen, serum creatinine and the tubular damage score after injury. Post-I/R injury AS1842856 treatment could also ameliorate renal function and improve the survival rate of mice following injury. AS1842856 administration reduced mitochondrial-mediated apoptosis, suppressed the overproduction of mitochondrial ROS and accelerated recovery of ATP both in vivo and in vitro. Additionally, FOXO1 inhibition improved mitochondrial biogenesis and suppressed mitophagy. Expression of PPAR-γ coactivator 1α (PGC-1α), a master regulator of mitochondrial biogenesis, was down-regulated in both I/R and H/R injury, which could be abrogated by FOXO1 inhibition. Experiments using integrated bioinformatics analysis and coimmunoprecipitation established that FOXO1 inhibited PGC-1α transcription by competing with cAMP-response element binding protein (CREB) for its binding to transcriptional coactivators CREBBP/EP300 (CBP/P300).

CONCLUSION AND IMPLICATIONS

These findings suggested that FOXO1 was critical to maintain mitochondrial function in renal tubular epithelial cells and FOXO1 may serve as a therapeutic target for pharmacological intervention in renal I/R injury.

Altered Brain Expression of Insulin and Insulin-Like Growth Factors in Frontotemporal Lobar Degeneration: Another Degenerative Disease Linked to Dysregulation of Insulin Metabolic Pathways

BACKGROUND

Frontotemporal lobar degeneration (FTLD) is the third most common dementing neurodegenerative disease with nearly 80% having no known etiology.

OBJECTIVE

Growing evidence that neurodegeneration can be linked to dysregulated metabolism prompted us to measure a panel of trophic factors, receptors, and molecules that modulate brain metabolic function in FTLD.

METHODS

Postmortem frontal (Brodmann's area [BA]8/9 and BA24) and temporal (BA38) lobe homogenates were used to measure immunoreactivity to Tau, phosphorylated tau (pTau), ubiquitin, 4-hydroxynonenal (HNE), transforming growth factor-beta 1 (TGF-β1) and its receptor (TGF-β1R), brain-derived neurotrophic factor (BDNF), nerve growth factor, neurotrophin-3, neurotrophin-4, tropomyosin receptor kinase, and insulin and insulin-like growth factor-1 (IGF-1) and insulin-like growth factor-2 (IGF-2) and their receptors by direct-binding enzyme-linked immunosorbent assay.

RESULTS

FTLD brains had significantly elevated pTau, ubiquitin, TGF-β1, and HNE immunoreactivity relative to control. In addition, BDNF and neurotrophin-4 were respectively reduced in BA8/9 and BA38, while neurotrophin-3 and nerve growth factor were upregulated in BA38, and tropomyosin receptor kinase was elevated in BA24. Lastly, insulin and insulin receptor expressions were elevated in the frontal lobe, IGF-1 was increased in BA24, IGF-1R was upregulated in all three brain regions, and IGF-2 receptor was reduced in BA24 and BA38.

CONCLUSIONS

Aberrantly increased levels of pTau, ubiquitin, HNE, and TGF-β1, marking neurodegeneration, oxidative stress, and neuroinflammation, overlap with altered expression of insulin/IGF signaling ligand and receptors in frontal and temporal lobe regions targeted by FTLD. Dysregulation of insulin-IGF signaling networks could account for brain hypometabolism and several characteristic neuropathologic features that characterize FTLD but overlap with Alzheimer's disease, Parkinson's disease, and Dementia with Lewy Body Disease.