The erythropoietin receptor expressed in skeletal muscle is essential for mitochondrial biogenesis and physiological exercise

A Kinase Interacting Protein 1 regulates mitochondrial protein levels in energy metabolism and promotes mitochondrial turnover after exercise

A Kinase Interacting Protein 1 (AKIP1) is a signalling adaptor that promotes mitochondrial respiration and attenuates mitochondrial oxidative stress in cultured cardiomyocytes. We sought to determine whether AKIP1 influences mitochondrial function and the mitochondrial adaptation in response to exercise in vivo. We assessed mitochondrial respiratory capacity, as well as electron microscopy and mitochondrial targeted-proteomics in hearts from mice with cardiomyocyte-specific overexpression of AKIP1 (AKIP1-TG) and their wild type (WT) littermates. These parameters were also assessed after four weeks of voluntary wheel running. In contrast to our previous in vitro study, respiratory capacity measured as state 3 respiration on palmitoyl carnitine was significantly lower in AKIP1-TG compared to WT mice, whereas state 3 respiration on pyruvate remained unaltered. Similar findings were observed for maximal respiration, after addition of FCCP. Mitochondrial DNA damage and oxidative stress markers were not elevated in AKIP1-TG mice and gross mitochondrial morphology was similar. Mitochondrial targeted-proteomics did reveal reductions in mitochondrial proteins involved in energy metabolism. Exercise performance was comparable between genotypes, whereas exercise-induced cardiac hypertrophy was significantly increased in AKIP1-TG mice. After exercise, mitochondrial state 3 respiration on pyruvate substrates was significantly lower in AKIP1-TG compared with WT mice, while respiration on palmitoyl carnitine was not further decreased. This was associated with increased mitochondrial fission on electron microscopy, and the activation of pathways associated with mitochondrial fission and mitophagy. This study suggests that AKIP1 regulates the mitochondrial proteome involved in energy metabolism and promotes mitochondrial turnover after exercise. Future studies are required to unravel the mechanistic underpinnings and whether the mitochondrial changes are required for the AKIP1-induced physiological cardiac growth.

Erythropoietin receptor is a risk factor for prognosis: A potential biomarker in lung adenocarcinoma

Lung cancer has the highest mortality rate of all cancers, and LUAD's survival rate is particularly poor. Erythropoietin receptor (EPOR) can be detected in lung adenocarcinoma (LUAD), however, the expression levels and prognostic value of EPOR in LUAD are still unclear. In our study, clinicopathological data of 92 LUAD patients between January 2008 and June 2016, multiple bioinformatics databases and immunohistochemistry were used to explore the EPOR expression, the mutant genes affecting EPOR expression, and the correlation of EPOR expression with oxidative stress - related genes, prognosis, immune microenvironment. All statistical analyses were performed in the R version 4.1.1. The study found that EPOR expression might be down-regulated at the mRNA levels and significantly up-regulated at the protein levels in LUAD, which indicates that the mRNA and protein levels of EPOR are inconsistent. The muTarget showed that the expression of EPOR was significantly different between the mutant group and the wild group of 15 genes, including DDX60L and C1orf168. Importantly, we found that EPOR was associated with VEGF and HIF family members, and had significant positive correlation with oxidative stress - related genes such as CCS, EPX and TXNRD2. This suggests that EPOR may be involved in the regulation of oxidative stress. The Kaplan-Meier Plotter and PrognoScan databases consistently concluded that EPOR was associated with prognosis in LUAD patients. Our clinicopathological data showed that high EPOR expression was associated with poorer overall survival (29.5 vs 46 months) and had a good predictive ability for 4-year and 5-year survival probability. EPOR is expected to be a potential new prognostic marker for LUAD.

Subchronic Arsenite Exposure Induced Atrophy and Erythropoietin Sensitivity Reduction in Skeletal Muscle Were Relevant to Declined Serum Melatonin Levels in Middle-Aged Rats

Arsenic is a kind of widespread environmental toxicant with multiorgan-toxic effects, and arsenic exposure is associated with the occurrence and development of many chronic diseases. The influence of environmental arsenic exposure on skeletal muscle, which is a vital organ of energy and glucose metabolism, has received increasing attention. This study aimed to investigate the types of inorganic arsenic-induced skeletal muscle injury, and the potential regulatory effects of melatonin (MT) and erythropoietin (EPO) in young (3-month-old) and middle-aged (12-month-old) rats. Our results showed that 1 mg/L sodium arsenite exposure for 3 months could accelerate gastrocnemius muscle atrophy and promote the switch of type II fibers to type I fibers in middle-aged rats; however, it did not cause significant pathological changes of gastrocnemius muscle in young rats. In addition, arsenite could inhibit serum MT levels, and promote serum EPO levels but inhibit EPO receptor (EPOR) expression in gastrocnemius muscle in middle-aged rats, while serum MT levels and EPOR expression in gastrocnemius muscle showed an opposite effect in young rats. Importantly, exogenous MT antagonized the arsenite-induced skeletal muscle toxic effect and restored serum EPO and gastrocnemius muscle EPOR expression levels in middle-aged rats. There was a positive correlation among gastrocnemius muscle index, serum MT level, and gastrocnemius muscle EPOR protein level in arsenite-exposed rats. This study demonstrated that inorganic arsenic could accelerate skeletal muscle mass loss and type II fiber reduction in middle-aged rats, which may be related to decreased MT secretion and declined EPO sensitivity in skeletal muscle.

A Kinase Interacting Protein 1 (AKIP1) promotes cardiomyocyte elongation and physiological cardiac remodelling

A Kinase Interacting Protein 1 (AKIP1) is a signalling adaptor that promotes physiological hypertrophy in vitro. The purpose of this study is to determine if AKIP1 promotes physiological cardiomyocyte hypertrophy in vivo. Therefore, adult male mice with cardiomyocyte-specific overexpression of AKIP1 (AKIP1-TG) and wild type (WT) littermates were caged individually for four weeks in the presence or absence of a running wheel. Exercise performance, heart weight to tibia length (HW/TL), MRI, histology, and left ventricular (LV) molecular markers were evaluated. While exercise parameters were comparable between genotypes, exercise-induced cardiac hypertrophy was augmented in AKIP1-TG vs. WT mice as evidenced by an increase in HW/TL by weighing scale and in LV mass on MRI. AKIP1-induced hypertrophy was predominantly determined by an increase in cardiomyocyte length, which was associated with reductions in p90 ribosomal S6 kinase 3 (RSK3), increments of phosphatase 2A catalytic subunit (PP2Ac) and dephosphorylation of serum response factor (SRF). With electron microscopy, we detected clusters of AKIP1 protein in the cardiomyocyte nucleus, which can potentially influence signalosome formation and predispose a switch in transcription upon exercise. Mechanistically, AKIP1 promoted exercise-induced activation of protein kinase B (Akt), downregulation of CCAAT Enhancer Binding Protein Beta (C/EBPβ) and de-repression of Cbp/p300 interacting transactivator with Glu/Asp rich carboxy-terminal domain 4 (CITED4). Concludingly, we identified AKIP1 as a novel regulator of cardiomyocyte elongation and physiological cardiac remodelling with activation of the RSK3-PP2Ac-SRF and Akt-C/EBPβ-CITED4 pathway. These findings suggest that AKIP1 may serve as a nodal point for physiological reprogramming of cardiac remodelling.

Pan-Cancer Analysis Based on EPOR Expression With Potential Value in Prognosis and Tumor Immunity in 33 Tumors

Background

Erythropoietin receptor (EPOR), a member of the cytokine class I receptor family, mediates erythropoietin (EPO)-induced erythroblast proliferation and differentiation, but its significance goes beyond that. The expression and prognosis of EPOR in cancer remain unclear.

Methods

This study intended to perform a pan-cancer analysis of EPOR by bioinformatics methods. Several databases such as GTEx, TCGA, CCLE, and others were used to explore the overall situation of EPOR expression, and the correlation of EPOR expression with prognosis, microRNAs (miRNAs), immune infiltration, tumor microenvironment, immune checkpoint genes, chemokines, tumor mutation burden (TMB), microsatellite instability (MSI), methyltransferases, and DNA mismatch repair (MMR) genes in 33 tumors was analyzed. In addition, we compared the promoter methylation levels of EPOR in cancer tissues with those in normal tissues and performed protein-protein interaction network, gene-disease network, and genetic alteration analyses of EPOR, and finally enrichment analysis of EPOR-interacting proteins, co-expressed genes, and differentially expressed genes.

Results

The TCGA database showed that EPOR expression was upregulated in BLCA, CHOL, HNSC, KIRC, LIHC, STAD, and THCA and downregulated in LUAD and LUSC. After combining the GTEx database, EPOR expression was found to be downregulated in 18 cancer tissues and upregulated in 6 cancer tissues. The CCLE database showed that EPOR expression was highest in LAML cell lines and lowest in HNSC cell lines. Survival analysis showed that high EPOR expression was positively correlated with OS in LUAD and PAAD and negatively correlated with OS in COAD, KIRC, and MESO. Moreover, EPOR had a good prognostic ability for COAD, LUAD, MESO, and PAAD and also influenced progression-free survival, disease-specific survival, disease-free survival, and progression-free interval in specific tumors. Further, EPOR was found to play a non-negligible role in tumor immunity, and a correlation of EPOR with miRNAs, TMB, MSI, and MMR genes and methyltransferases was confirmed to some extent. In addition, the enrichment analysis revealed that EPOR is involved in multiple cancer-related pathways.

Conclusion

The general situation of EPOR expression in cancer provided a valuable clinical reference. EPOR may be target gene of hsa-miR-575, etc. A pan-cancer analysis of panoramic schema revealed that EPOR not only may play an important role in mediating EPO-induced erythroblast proliferation and differentiation but also has potential value in tumor immunity and is expected to be a prognostic marker for specific cancers.

Exercise: a molecular tool to boost muscle growth and mitochondrial performance in heart failure?

Impaired exercise capacity is the key symptom of heart failure (HF) and is associated with reduced quality of life and higher mortality rates. Unfortunately, current therapies, although generally lifesaving, have only small or marginal effects on exercise capacity. Specific strategies to alleviate exercise intolerance may improve quality of life, while possibly improving prognosis as well. There is overwhelming evidence that physical exercise improves performance in cardiac and skeletal muscles in health and disease. Unravelling the mechanistic underpinnings of exercise‐induced improvements in muscle function could provide targets that will allow us to boost exercise performance in HF. With the current review we discuss: (i) recently discovered signalling pathways that govern physiological muscle growth as well as mitochondrial quality control mechanisms that underlie metabolic adaptations to exercise; (ii) the mechanistic underpinnings of exercise intolerance in HF and the benefits of exercise in HF patients on molecular, functional and prognostic levels; and (iii) potential molecular therapeutics to improve exercise performance in HF. We propose that novel molecular therapies to boost adaptive muscle growth and mitochondrial quality control in HF should always be combined with some form of exercise training.

Physical Training Increases Erythroferrone Levels in Men

Intense physical activity contributes to an increased demand for red blood cells, which transport oxygen to working muscles. The purpose of this study was to assess the concentration of erythroferrone (ERFE), the novel marker of erythroid activity in athletes, during the beginning of their training season. The study group consisted of 39 athletes aged 23.24 ± 3.77 years. The study was carried out during the athletes' preparatory period of the training cycle. The control group consisted of 34 healthy men aged 22.33 ± 2.77 years. The erythropoietic activity was evaluated by determining athletes' concentrations of erythropoietin (EPO) and erythroferrone (ERFE). The level of physical activity was assessed using the International Physical Activity Questionnaire (IPAQ). In the athletes' group, we observed higher concentrations of EPO (Me = 12.65 mIU/mL) and ERFE (40.00 pg/mL) compared to the control group (EPO: Me = 5.74 mIU/ml, p = 0.001; ERFE: Me = 25.50 pg/mL, p = 0.0034). The average intensity of physical exercise significantly differentiated the participants as far as EPO and ERFE concentrations. These results suggest that intense physical activity, at least at the beginning of the training season, may stimulate EPO production, which increases ERFE release. This seems to be an adaptative mechanism that provides adequate iron for enhanced erythropoiesis.

Acute erythropoietin injection increases muscle mitochondrial respiratory capacity in young men: a double-blinded randomized crossover trial

The aim was to investigate if acute recombinant human erythropoietin (rHuEPO) injection had an effect on mitochondrial function and if exercise would have an additive effect. Furthermore, to investigate if in vitro incubation with rHuEPO had an effect on muscle mitochondrial respiratory capacity. Eight healthy young men were recruited for this double-blinded randomized placebo-controlled crossover study. rHuEPO (400 IU/kg body wt) or saline injection was given intravenously, before an acute bout of exercise. Resting metabolic rate and fat oxidation were measured. Biopsies were obtained at baseline, 120 min after injection, and right after the acute exercise bout. Mitochondrial function (mitochondrial respiration and H₂O₂ emission) was measured in permeabilized skeletal muscle using high-resolution respirometry and fluorometry. Specific gene expression and enzyme activity were measured. Skeletal muscle mitochondrial respiratory capacity was measured with and without incubation with rHuEPO. Fat oxidation at rest increased after rHuEPO injection, but no difference was found in fat oxidation during exercise. Mitochondrial respiratory capacity was increased after rHuEPO injection when pyruvate was in the assay, which was not the case when saline was injected. No changes were seen in H₂O₂ emission after rHuEPO injection or acute exercise. Incubation of skeletal muscle fibers in vitro with rHuEPO increased mitochondrial respiratory capacity. Acute rHuEPO injection increased mitochondrial respiratory capacity when pyruvate was used in the assay. No statistical difference was found in H₂O₂ emission capacity, although a numerical increase was seen after rHuEPO injection. In vitro incubation of the skeletal muscle sample with rHuEPO increases mitochondrial respiratory capacity.NEW & NOTEWORTHY The effect of an acute rHuEPO injection on skeletal muscle mitochondrial function was investigated in young healthy male subjects. rHuEPO has an acute effect on skeletal muscle mitochondrial respiratory capacity in humans, where an increased mitochondrial respiratory capacity was seen. This could be the first step leading to increased mitochondrial biogenesis.