Mathematical modeling reveals modulation of both nuclear influx and efflux of Foxo1 by the IGF-I/PI3K/Akt pathway in skeletal muscle fibers

The ability to sense the environment is heterogeneously distributed in cell populations

Channel capacity of signaling networks quantifies their fidelity in sensing extracellular inputs. Low estimates of channel capacities for several mammalian signaling networks suggest that cells can barely detect the presence/absence of environmental signals. However, given the extensive heterogeneity and temporal stability of cell state variables, we hypothesize that the sensing ability itself may depend on the state of the cells. In this work, we present an information-theoretic framework to quantify the distribution of sensing abilities from single-cell data. Using data on two mammalian pathways, we show that sensing abilities are widely distributed in the population and most cells achieve better resolution of inputs compared to an 'average cell'. We verify these predictions using live-cell imaging data on the IGFR/FoxO pathway. Importantly, we identify cell state variables that correlate with cells' sensing abilities. This information-theoretic framework will significantly improve our understanding of how cells sense in their environment.

The ability to sense the environment is heterogeneously distributed in cell populations

Channel capacity of signaling networks quantifies their fidelity in sensing extracellular inputs. Low estimates of channel capacities for several mammalian signaling networks suggest that cells can barely detect the presence/absence of environmental signals. However, given the extensive heterogeneity and temporal stability of cell state variables, we hypothesize that the sensing ability itself may depend on the state of the cells. In this work, we present an information theoretic framework to quantify the distribution of sensing abilities from single cell data. Using data on two mammalian pathways, we show that sensing abilities are widely distributed in the population and most cells achieve better resolution of inputs compared to an " average cell ". We verify these predictions using live cell imaging data on the IGFR/FoxO pathway. Importantly, we identify cell state variables that correlate with cells' sensing abilities. This information theoretic framework will significantly improve our understanding of how cells sense in their environment.

Molecular and metabolic mechanisms of bufalin against lung adenocarcinoma: New and comprehensive evidences from network pharmacology, metabolomics and molecular biology experiment

BACKGROUND

This study aims to evaluate the efficacy and therapeutic mechanism of bufalin on lung adenocarcinoma (LUAD) through a comprehensive strategy integrating network pharmacology, metabolomics and molecular biology verification.

METHODS

The putative targets of bufalin were discerned from PharmMapper and Swiss Target Prediction database. LUAD-related targets were obtained by target filtering of GeneCard database and data mining of GEO database. PPI network was constructed to screen the core targets, and their clinical significance was assessed through several public databases. GO and KEGG pathway analyses were performed to identify possible enrichment of genes with specific biological themes. Molecular docking and molecular dynamics (MD) simulation were employed to determine the correlation and binding pattern between bufalin and core targets. The potential mechanisms of bufalin acting on LUAD, as predicted by network pharmacology analyses, were experimentally validated using in-vitro and in-vivo models. Finally, the effects of bufalin intervention on metabolite profile and metabolic pathway in LUAD nude mice were investigated by non-targeted metabolomics.

RESULTS

209 bufalin targets and 1082 LUAD-associated targets were harvested, of which 51 intersection targets were identified. 10 core targets including Akt1, STAT3, EGFR, CASP3 and SRC were picked out through network topology analysis, and they had a potent binding activity with bufalin as indicated by molecular docking and MD simulation. Hub module of PPI network was closely related to cell proliferation and apoptosis. GO and KEGG enrichment analyses suggested that bufalin exerted therapeutic effects on LUAD possibly by inhibiting proliferation and promoting apoptosis via PI3K/Akt, FoxO1 and MAPK/ERK pathways, which were confirmed by a series of in-vitro studies as well as HE, TUNEL and Ki-67 staining of tumor tissues. Further metabolomics analysis revealed that bufalin mainly regulated ABC transporter and remodeled AA metabolism, thereby contributing to the treatment of LUAD.

CONCLUSION

From molecular and metabolic perspective, the present study not only provided a unique insight into the possible mechanisms of bufalin against LUAD after successfully filtering out associated key target genes, differential endogenous metabolites, and signaling pathways, but also proposed a novel promising therapeutic strategy for LUAD.

Transcriptome analysis of breast muscle and liver in full-sibling hybrid broilers at different ages

In China, the production mode of hybrid broilers with meat-type chicken as male parent and egg-type chicken as female parent is common, but few studies pay attention to the economic characteristics of hybrid broilers. In this experiment, we constructed a full-sib F1 population (n = 57) from male Recursive White broiler and female Lohmann Pink layer. Total 6, 6 and 7 hybrid broilers at days 1, 28 and 56 were selected randomly to collect breast muscle and liver tissues, respectively. After performing strand-specific RNA-Seq on these samples, we obtained 252.12 Gb sequencing data. Principal component analysis presented that the effects of different factors on gene expression were as below: tissue difference > age difference > sex difference. The ten genes with the highest expression in breast muscle were GAPDH, ACTA1, ATP2B3, COII, ATP6, COX3, COX1, MYL1, TNNI2 and ENSGALG00000042024. Through the analysis of differentially expressed transcripts (DETs) between different ages, we found that the number of DETs decreased progressively with the prolongation of ages in breast muscle. The same results were also observed in liver. GO enrichment analysis of DETs demonstrated that total 11 BP terms closely related to growth and development of breast muscle were annotated, such as cardiac muscle contract, muscle contract, cell division and so on. KEGG annotation presented that total 5 pathways related to growth and development were determined in breast muscle, including Cell cycle, Insulin signaling pathway, FoxO signaling pathway, Focal adhesion and Adrenergic signaling in cardiomyocytes. Our results may provide theoretical foundation for hybrid broiler production.

Linalool Prevents Cisplatin Induced Muscle Atrophy by Regulating IGF-1/Akt/FoxO Pathway

Skeletal muscle atrophy is an important feature of cancer cachexia, which can be induced by chemotherapy, and affects the survival and quality of life of cancer patients seriously. No specific drugs for cancer cachexia have been applied in clinical practice. This study explored the therapeutic effect of linalool (LIN) on cisplatin (DDP) induced skeletal muscle atrophy. In vivo, LIN can improve skeletal muscle weight loss, anorexia, muscle strength decline and other cachexia symptoms caused by cisplatin treatment in a Lewis lung cancer tumor bearing mouse model, and cause no adverse effects on the anti-tumour effect. LIN treatment decreased the expression of muscle RING-finger protein-1 (MuRF1) and Atrogin1(MAFbx) in muscle, and the activation of insulin-like growth factor-1 (IGF-1)/protein kinase B (Akt)/forkhead box O (FoxO) pathway was observed. In vitro, LIN alleviated DDP induced C2C12 myotube atrophy, and IGF-1 receptor inhibitor Picropodophyllin (PIC), which had no adverse effect on C2C12 myotube cells, could reverse the protective effect of LIN. These results indicate that LIN down-regulates the expression of Atrogin1 and MuRF1 through the IGF-1/Akt/FoxO pathway, alleviating DDP-induced muscle atrophy and improving cachexia symptoms. LIN has the potential to be developed as a drug against cancer cachexia.

Alternative signaling pathways from IGF1 or insulin to AKT activation and FOXO1 nuclear efflux in adult skeletal muscle fibers

Muscle atrophy is regulated by the balance between protein degradation and synthesis. FOXO1, a transcription factor, helps to determine this balance by activating pro-atrophic gene transcription when present in muscle fiber nuclei. Foxo1 nuclear efflux is promoted by AKT-mediated Foxo1 phosphorylation, eliminating FOXO1's atrophy-promoting effect. AKT activation can be promoted by insulin-like growth factor 1 (IGF1) or insulin via a pathway including IGF1 or insulin, phosphatidylinositol 3-kinase, and AKT. We used confocal fluorescence time-lapse imaging of FOXO1-GFP in adult isolated living muscle fibers maintained in culture to explore the effects of IGF1 and insulin on FOXO1-GFP nuclear efflux with and without pharmacological inhibitors. We observed that although AKT inhibitor blocks the IGF1- or insulin-induced effect on FOXO1 nuclear efflux, phosphatidylinositol 3-kinase inhibitors, which we show to be effective in these fibers, do not. We also found that inhibition of the protein kinase ACK1 or ATM contributes to the suppression of FOXO1 nuclear efflux after IGF1. These results indicate a novel pathway that has been unexplored in the IGF1- or insulin-induced regulation of FOXO1 and present information useful both for therapeutic interventions for muscle atrophy and for further investigative areas into insulin insensitivity and type 2 diabetes.

High-intensity interval training-induced hypertrophy in gastrocnemius muscle via improved IGF-I/Akt/FoxO and myostatin/Smad signaling pathways in rats

Objective

It has been shown that high-intensity interval training (HIIT) leads to skeletal muscle hypertrophy; however, its mechanisms of cellular and molecular regulation are still unclear. The purpose of this study was to investigate the effect of HIIT on muscle hypertrophy and major signal transduction pathways.

Design

12 male rats were randomly divided into two groups: control and HIIT. The exercise group performed 30-min HIIT in each session (5 × 4-min intervals running at 85-95% VO2max separated by 2-min active rest at 55-60% VO2max), 3 days/week for 8 weeks. Muscle fiber cross-sectional area (CSA) and the expression of signal transduction pathway proteins were determined in the gastrocnemius muscle.

Results

In the HIIT group, the expression of IGF-I, IGF-IR Akt, p-Akt, AMPKα, p-AMPKα and follistatin increased significantly, whereas a significant decrease was observed in the expression of FoxO1, p-FoxO1, myostatin, ActRIIB, Smad2/3 and p-Smad2/3 (P < 0.05). However, there were no significant differences between the HIIT and control groups in the expression of mTOR, p-mTOR, P70S6K, and p-P70S6K (P > 0.05). In addition, CSA and gastrocnemius muscle weight increased significantly in the HIIT group (P < 0.05).

Conclusions

HIIT induced muscle hypertrophy by improving IGF-I/Akt/FoxO and myostatin/Smad signal transduction pathways.

Mathematical Modeling of Nuclear Trafficking of FOXO Transcription Factors

Nuclear cytoplasmic flux of Foxo transcription factors is paramount in cellular gene regulation. For example, excluding Foxo from skeletal muscle nuclei is necessary to avoid muscle wasting through elevated protein breakdown. Constructing a mathematical model of the signaling process leading to alteration of Foxo nuclear cytoplasm ratio is useful in predicting and interpreting such ratio changes. In this chapter we derive a general mathematical model for nuclear cytoplasmic flux. We apply this model to Foxo flux and take advantage of rapid phosphorylation approximation and conservation conditions to reduce the Foxo flux model. We constrain our model with data from mouse skeletal muscle with applied IGF. This procedure provides an example of what might be called the central approach of mathematical modeling: The cycling of a biological question through mathematical formulation and back to biological interpretation.

Transplantation of UC-MSCs on collagen scaffold activates follicles in dormant ovaries of POF patients with long history of infertility

Premature ovarian failure (POF) is a refractory disease for clinical treatment with the goal of restoring fertility. In this study, umbilical cord mesenchymal stem cells on a collagen scaffold (collagen/UC-MSCs) can activate primordial follicles in vitro via phosphorylation of FOXO3a and FOXO1. Transplantation of collagen/UC-MSCs to the ovaries of POF patients rescued overall ovarian function, evidenced by elevated estradiol concentrations, improved follicular development, and increased number of antral follicles. Successful clinical pregnancy was achieved in women with POF after transplantation of collagen/UC-MSCs or UC-MSCs. In summary, collagen/UC-MSC transplantation may provide an effective treatment for POF.

Foxo1 nucleo-cytoplasmic distribution and unidirectional nuclear influx are the same in nuclei in a single skeletal muscle fiber but vary between fibers

Foxo transcription factors promote protein breakdown and atrophy of skeletal muscle fibers. Foxo transcriptional effectiveness is largely determined by phosphorylation-dependent nucleo-cytoplasmic shuttling. Imaging Foxo1-green fluorescent protein (GFP) over time in 124 nuclei in 68 multinucleated adult skeletal muscle fibers under control culture conditions reveals large variability between fibers in Foxo1-GFP nucleo-cytoplasmic concentration ratio (N/C) and in the apparent rate coefficient ( kI') for Foxo1-GFP unidirectional nuclear influx (measured with efflux blocked by leptomycin B). Pairs of values of N/C or of kI' from different nuclei in the same fiber were essentially the same, but only weakly correlated in nuclei from different fibers in the same culture well. Thus, fiber to fiber variability of cellular factors, but not extracellular factors, determines Foxo1 distribution. Over all nuclei, N/C and kI' were closely proportional, indicating that kI' is the major determinant of Foxo1 distribution. IGF-I activation of Foxo kinase Akt reduces variability by decreasing kI' and N/C in all fibers. However, inhibiting Akt did not drive kI' uniformly high, indicating other pathways in Foxo1 regulation.

Low-Intensity Pulsed Ultrasound Promotes Exercise-Induced Muscle Hypertrophy

The purpose of this study was to investigate whether low-intensity pulsed ultrasound (LIPUS) promotes exercise-induced muscle hypertrophy. Twenty-four adult Sprague-Dawley (SD) rats were randomly assigned to three groups (n = 8 per group): normal control group (NC), treadmill exercise group (TE) and treadmill exercise + LIPUS group (TE + LIPUS). The TE + LIPUS group received a LIPUS treatment (1 MHz, 30 mW/cm²) at the gastrocnemius for 20 min/d after treadmill exercise. The TE group was sham-treated. Eight weeks of treadmill training successfully established the exercise-induced muscle hypertrophy model. Muscle strength, muscle mass and muscle fiber cross-sectional area were significantly increased in the TE + LIPUS group compared with the TE group. Moreover, LIPUS treatment significantly upregulated the expression of Akt, mTOR, p-Akt and p-mTOR and significantly downregulated the expression of MSTN, ActRIIB, FoxO1 and its phosphorylation. The results indicated that LIPUS promotes exercise-induced muscle hypertrophy by facilitating protein synthesis and inhibiting the protein catabolism pathway.

Modelling the molecular mechanisms of aging

The aging process is driven at the cellular level by random molecular damage that slowly accumulates with age. Although cells possess mechanisms to repair or remove damage, they are not 100% efficient and their efficiency declines with age. There are many molecular mechanisms involved and exogenous factors such as stress also contribute to the aging process. The complexity of the aging process has stimulated the use of computational modelling in order to increase our understanding of the system, test hypotheses and make testable predictions. As many different mechanisms are involved, a wide range of models have been developed. This paper gives an overview of the types of models that have been developed, the range of tools used, modelling standards and discusses many specific examples of models that have been grouped according to the main mechanisms that they address. We conclude by discussing the opportunities and challenges for future modelling in this field.

Long-term exposure to abnormal glucose levels alters drug metabolism pathways and insulin sensitivity in primary human hepatocytes

Hyperglycemia in type 2 diabetes mellitus has been linked to non-alcoholic fatty liver disease, which can progress to inflammation, fibrosis/cirrhosis, and hepatocellular carcinoma. Understanding how chronic hyperglycemia affects primary human hepatocytes (PHHs) can facilitate the development of therapeutics for these diseases. Conversely, elucidating the effects of hypoglycemia on PHHs may provide insights into how the liver adapts to fasting, adverse diabetes drug reactions, and cancer. In contrast to declining PHH monocultures, micropatterned co-cultures (MPCCs) of PHHs and 3T3-J2 murine embryonic fibroblasts maintain insulin-sensitive glucose metabolism for several weeks. Here, we exposed MPCCs to hypo-, normo- and hyperglycemic culture media for ~3 weeks. While albumin and urea secretion were not affected by glucose level, hypoglycemic MPCCs upregulated CYP3A4 enzyme activity as compared to other glycemic states. In contrast, hyperglycemic MPCCs displayed significant hepatic lipid accumulation in the presence of insulin, while also showing decreased sensitivity to insulin-mediated inhibition of glucose output relative to a normoglycemic control. In conclusion, we show for the first time that PHHs exposed to hypo- and hyperglycemia can remain highly functional, but display increased CYP3A4 activity and selective insulin resistance, respectively. In the future, MPCCs under glycemic states can aid in novel drug discovery and mechanistic investigations.

Green tea component EGCG, insulin and IGF-1 promote nuclear efflux of atrophy-associated transcription factor Foxo1 in skeletal muscle fibers

Prevention and slowing of skeletal muscle atrophy with nutritional approaches offers the potential to provide far-reaching improvements in the quality of life for our increasingly aging population. Here we show that polyphenol flavonoid epigallocatechin 3-gallate (EGCG), found in the popular beverage green tea (Camellia sinensis), demonstrates similar effects to the endogenous hormones insulin-like growth factor 1 (IGF-1) and insulin in the ability to suppress action of the atrophy-promoting transcription factor Foxo1 through a net translocation of Foxo1 out of the nucleus as monitored by nucleo-cytoplasmic movement of Foxo1-green fluorescent protein (GFP) in live skeletal muscle fibers. Foxo1-GFP nuclear efflux is rapid in IGF-1 or insulin, but delayed by an additional 30 min for EGCG. Once activated, kinetic analysis with a simple mathematical model shows EGCG, IGF-1 and insulin all produce similar apparent rate constants for Foxo1-GFP unidirectional nuclear influx and efflux. Interestingly, EGCG appears to have its effect at least partially via parallel signaling pathways that are independent of IGF-1's (and insulin's) downstream PI3K/Akt/Foxo1 signaling axis. Using the live fiber model system, we also determine the dose-response curve for both IGF-1 and insulin on Foxo1 nucleo-cytoplasmic distribution. The continued understanding of the activation mechanisms of EGCG could allow for nutritional promotion of green tea's antiatrophy skeletal muscle benefits and have implications in the development of a clinically significant parallel pathway for new drugs to target muscle wasting and the reduced insulin receptor sensitivity which causes type II diabetes mellitus.

Insulin-like growth factor-1 (IGF-1) promotes myoblast proliferation and skeletal muscle growth of embryonic chickens via the PI3K/Akt signalling pathway

During embryonic development, IGF-1 fulfils crucial roles in skeletal myogenesis. However, the involvement of IGF-1-induced myoblast proliferation in muscle growth is still unclear. In the present study, we have characterised the role of IGF-1 in myoblast proliferation both in vitro and in vivo and have revealed novel details of how exogenous IGF-1 influences myogenic genes in chicken embryos. The results show that IGF-1 significantly induces the proliferation of cultured myoblasts in a dose-dependent manner. Additionally, the IGF-1 treatment significantly promoted myoblasts entering a new cell cycle and increasing the mRNA expression levels of cell cycle-dependent genes. However, these effects were inhibited by the PI3K inhibitor LY294002 and the Akt inhibitor KP372-1. These data indicated that the pro-proliferative effect of IGF-1 was mediated in response to the PI3K/Akt signalling pathway. Moreover, we also showed that exogenous IGF-1 stimulated myoblast proliferation in vivo. IGF-1 administration obviously promoted the incorporation of BrdU and remarkably increased the number of PAX7-positive cells in the skeletal muscle of chicken embryos. Administration of IGF-1 also significantly induced the upregulation of myogenic factors gene, the enhancement of c-Myc and the inhibition of myostatin (Mstn) expression. These findings demonstrate that IGF-1 has strong activity as a promoter of myoblast expansion and muscle fiber formation during early myogenesis. Therefore, this study offers insight into the mechanisms responsible for IGF-1-mediated stimulation of embryonic skeletal muscle development, which could have important implications for the improvement of chicken meat production.