IGFBP-5 regulates muscle cell differentiation by binding to IGF-II and switching on the IGF-II auto-regulation loop

Cellular Activity Modulation Mediated by Near Infrared-Irradiated Polydopamine Nanoparticles: In Vitro and Ex Vivo Investigation

The precise control of cell activity is crucial for understanding and potentially treating many disorders. Focusing on neurons and myotubes, recent advancements in nanotechnology have introduced photoresponsive nanoparticles as an alternative tool for modulating cell function with high spatial and temporal resolution. This approach offers a noninvasive alternative to traditional stimulation techniques, reducing potential tissue damage and improving the specificity of cell activation. Here, we introduce an approach envisioning fully organic polydopamine nanoparticles (PDNPs) to remotely modulate the activity of differentiated SH-SY5Y cells and differentiated C2C12 cells, via near-infrared (NIR) laser stimulation. Confocal microscopy imaging revealed the possibility of thermally activating individual neuron-like cells, eliciting a significant cellular response characterized by the generation of calcium transients and the subsequent release of the neurotransmitter acetylcholine. Similarly, we demonstrated the possibility of precisely triggering the muscle contraction of single myotubes. Additionally, we investigated the antioxidant properties of PDNPs, demonstrating their capacity to prevent an increase in oxidative stress levels related to an increase in intracellular temperature. Moreover, proteomic analysis revealed that a PDNP treatment could positively affect neuronal plasticity and nervous system maturation, besides promoting muscle growth and preserving its functional integrity, underscoring its potential to support both neural and musculoskeletal development. Eventually, the effect of the NIR laser irradiation in the presence of PDNPs in neuron-like cells was successfully evaluated ex vivo on brains of Drosophila melanogaster, genetically modified to express the fluorescent calcium indicator jGCaMP7c.

Myogenic IGFBP5 levels in rhabdomyosarcoma are nourished by mesenchymal stromal cells and regulate growth arrest and apoptosis

BACKGROUND

Mesenchymal stromal cells belong to a diverse collection of cells in different states that are poorly characterized in soft-tissue sarcomas. In this study, we explored tumor growth-regulatory signaling between differentially educated non-malignant mesenchymal stromal cells and malignant cells in pediatric rhabdomyosarcoma (RMS).

METHODS

Xenograft experiments demonstrated that non-malignant stromal cells influence tumor behavior. Gene expression analysis identified deregulated genes, which were further studied using cell culture assays and patient data. Clinicopathological correlations were made in a discovery cohort (N = 147) and a validation cohort (N = 101).

RESULTS

The results revealed transiently suppressive paracrine effects of orthotopic stromal cells derived from skeletal muscle. These effects were lost when the stromal cells were exposed to RMS cells, either short-term in vitro, or long-term in hindlimb muscle in vivo. High resolution microarray-based Clariom D gene expression analysis identified insulin-like growth factor binding protein 5 (IGFBP5) as the top upregulated gene in RMS cells exposed to naïve stromal cells, and effects on growth arrest, caspase 3/7 activation, and myogenic cell identity were demonstrated in functional assays. Furthermore, IGFBP5 associated with the caspase 3 substrate growth arrest specific protein 2 (GAS2), lower disease stage and favorable survival in patient cohorts.

CONCLUSIONS

This study uses functional modeling and omics approaches to identify IGFBP5 as a candidate mediator of anti-tumor growth mechanisms originating from tumor-neighboring mesenchymal stromal cells. Tumors of mesenchymal origin, such as RMS, are known for their heterogeneity, and this could potentially pose a limitation to the study. However, a clinical relevance is emphasized by consistent findings across patient cohorts. These insights pave the way for novel therapeutic strategies modulating activities of stromal cell subsets at primary and metastatic sites in RMS.

LMNA R482L mutation causes impairments in C2C12 myoblasts subpopulations, alterations in metabolic reprogramming during differentiation, and oxidative stress

LMNA mutations causing classical familial partial lipodystrophy of Dunnigan type (FPLD2) usually affect residue R482. FPLD is a severe metabolic disorder that often leads to cardiovascular and skeletal muscle complications. How LMNA mutations affect the functional properties of skeletal muscles is still not well understood. In the present project, we investigated the LMNA-R482L mutation-specific alterations in a transgenic mouse C2C12 cell line of myoblasts. Using single-cell RNA sequencing we have studied transcriptional diversity of cultured in vitro C2C12 cells. The LMNA-R482L mutation induces changes in C2C12 cluster composition and increases the expression of genes related to connective tissue development, oxidative stress, stress defense, and autophagy in a population-specific manner. Bulk RNA-seq confirmed these results and revealed the dysregulation of carbohydrate metabolism in differentiated R482L myotubes that was supported by ATP production profile evaluation. The measurement of reactive oxygen species (ROS) levels and glutathione accumulation in myoblasts and myotubes indicates R482L mutation-related dysregulation in mechanisms that control ROS production and scavenging through antioxidant glutathione system. The increased accumulation of autophagy-related structures in R482L myoblasts was also shown. Overall, our experiments showed a connection between the redox status and metabolic alterations with skeletal muscle pathological phenotypes in cells bearing pathogenic LMNA mutation.

Regulation and function of insulin and insulin-like growth factor receptor signalling

Receptors of insulin and insulin-like growth factors (IGFs) are receptor tyrosine kinases whose signalling controls multiple aspects of animal physiology throughout life. In addition to regulating metabolism and growth, insulin-IGF receptor signalling has recently been linked to a variety of new, cell type-specific functions. In the last century, key questions have focused on how structural differences of insulin and IGFs affect receptor activation, and how insulin-IGF receptor signalling translates into pleiotropic biological functions. Technological advances such as cryo-electron microscopy have provided a detailed understanding of how native and engineered ligands activate insulin-IGF receptors. In this Review, we highlight recent structural and functional insights into the activation of insulin-IGF receptors, and summarize new agonists and antagonists developed for intervening in the activation of insulin-IGF receptor signalling. Furthermore, we discuss recently identified regulatory mechanisms beyond ligand-receptor interactions and functions of insulin-IGF receptor signalling in diseases.

Profiling growth performance, insulin-like growth factors, and IGF-binding proteins in rainbow trout lacking IGFBP-2b

Insulin-like growth factor-binding proteins (IGFBPs) regulate insulin-like growth factor (IGF) signaling, but IGFBP-specific functions are not well characterized in fishes. A line of rainbow trout (Oncorhynchus mykiss) lacking a functional IGFBP-2b was produced using gene editing and subsequent breeding to an F2 generation. This loss-of-function model [IGFBP-2b knockout (2bKO)] was subjected to either continuous feeding or feed deprivation (3 wk) followed by refeeding (1 wk). During continuous feeding, the 2bKO line displayed faster specific growth rate for both body weight and fork length, higher feed intake, and reduced feed conversion ratio compared with a wild-type (WT) line. However, loss of IGFBP-2b did not affect the feed deprivation or refeeding response in terms of weight loss or weight gain, respectively. Several components of the IGF/IGFBP system were affected by loss of IGFBP-2b. Total serum IGF-1 in the 2bKO line was reduced to 0.5- to 0.8-fold of the WT line, although the concentration of free serum IGF-1 was not affected. Gene expression differences include reduced abundance of igfbp1a1, igfbp1b2, igfbp5b2, and igfbp6b1 transcripts and elevated igf2 and igfbp6b2 transcripts in liver of the 2bKO line. Collectively, these findings suggest that although IGFBP-2b is a carrier of circulating IGF-1 in salmonids, the presence of IGFBP-2a and compensatory responses of other IGF/IGFBP system components support an anabolic response that improved growth performance in the loss-of-function model.NEW & NOTEWORTHY Knocking out IGFBP-2b in rainbow trout improved food intake, growth performance, and feed conversion ratio and reduced serum IGF-1 by 0.5- to 0.8-fold, without changes in the concentration of free serum IGF-1. Based on these findings, we propose that, in addition to IGFBP-2b, the 32-kDa IGFBP (putative IGFBP-2a) also serves as a major carrier of circulating IGF-1 in salmonids.

Loss or inhibition of lysosomal acid lipase in vitro leads to cholesteryl ester accumulation without affecting muscle formation or mitochondrial function

Skeletal muscle (SM) is essential for movement, stability, and overall body function, and it readily adapts to changes in energy demand. Myogenesis is energy-intensive and involves complex molecular and cellular events. We recently demonstrated that the absence of lysosomal acid lipase (LAL) in vivo significantly impacts the SM phenotype, primarily by disrupting energy homeostasis and reducing ATP production. As systemic LAL deficiency affects multiple organs, we hypothesized that the altered SM phenotype resulted from systemic rather than SM-specific loss of LAL activity. To distinguish between systemic and cell-intrinsic effects, we used primary myoblasts isolated from Lal-deficient (-/-) mice as well as C2C12 cells treated with the pharmacological inhibitor of LAL, Lalistat-2. We found a significant accumulation of cholesteryl esters in both models studied, highlighting the central role of LAL in lipid catabolism in the SM. However, lipid accumulation was absent under lipoprotein-deficient culture conditions. Neither genetic loss nor pharmacological inhibition of LAL affected myofiber formation or mitochondrial function in vitro, in contrast to what we observed in SM isolated from Lal-/- mice. Tracing [13C6]-labeled glucose in both cell culture models revealed only minor changes in tricarboxylic acid cycle metabolites. These results suggest that although LAL plays an essential role in lipid metabolism, its impact on the processes involved in muscle differentiation and cellular energy production is minor. We conclude that the cell-intrinsic effects of Lal-/- SM are unlikely to drive the SM phenotype observed in vivo.

IGF2 promotes the differentiation of chicken embryonic myoblast by regulating mitochondrial remodeling

Skeletal muscle is crucial for animal movement and posture maintenance, and it serves as a significant source of meat in the livestock and poultry industry. The number of muscle fibers differentiated from myoblast in the embryonic stage is one of the factors determining the content of skeletal muscle. Insulin-like growth factor 2 (IGF2), a well-known growth-promoting hormone, is crucial for embryonic and skeletal muscle growth and development. However, the specific molecular mechanism underlying its impact on chicken embryonic myoblast differentiation remains unclear. To elucidate the molecular mechanism by which IGF2 regulates chicken myoblast differentiation, we manipulated IGF2 expression in chicken embryonic myoblast. The results demonstrated that IGF2 was upregulated during chicken skeletal muscle development and myoblast differentiation. On the one hand, we found that IGF2 promotes mitochondrial biogenesis through the PGC1/NRF1/TFAM pathway, thereby enhancing mitochondrial membrane potential, oxidative phosphorylation, and ATP synthesis during myoblast differentiation. This process is mediated by the PI3K/AKT pathway. On the other hand, IGF2 regulates BNIP3-mediated mitophagy, clearing dysfunctional mitochondria. Collectively, our findings confirmed that IGF2 cooperatively regulates mitochondrial biogenesis and mitophagy to remodel the mitochondrial network and enhance mitochondrial function, ultimately promoting myoblast differentiation.

Investigating the basis of lineage decisions and developmental trajectories in the dorsal spinal cord through pseudotime analyses

Dorsal interneurons (dIs) in the spinal cord encode the perception of touch, pain, heat, itchiness and proprioception. Previous studies using genetic strategies in animal models have revealed important insights into dI development, but the molecular details of how dIs arise as distinct populations of neurons remain incomplete. We have developed a resource to investigate dI fate specification by combining a single-cell RNA-Seq atlas of mouse embryonic stem cell-derived dIs with pseudotime analyses. To validate this in silico resource as a useful tool, we used it to first identify genes that are candidates for directing the transition states that lead to distinct dI lineage trajectories, and then validated them using in situ hybridization analyses in the developing mouse spinal cord in vivo. We have also identified an endpoint of the dI5 lineage trajectory and found that dIs become more transcriptionally homogeneous during terminal differentiation. This study introduces a valuable tool for further discovery about the timing of gene expression during dI differentiation and demonstrates its utility in clarifying dI lineage relationships.

Investigating the basis of lineage decisions and developmental trajectories in the dorsal spinal cord through pseudotime analyses

Dorsal interneurons (dIs) in the spinal cord encode the perception of touch, pain, heat, itch, and proprioception. While previous studies using genetic strategies in animal models have revealed important insights into dI development, the molecular details by which dIs arise as distinct populations of neurons remain incomplete. We have developed a resource to investigate dI fate specification by combining a single-cell RNA-Seq atlas of mouse ESC-derived dIs with pseudotime analyses. To validate this in silico resource as a useful tool, we used it to first identify novel genes that are candidates for directing the transition states that lead to distinct dI lineage trajectories, and then validated them using in situ hybridization analyses in the developing mouse spinal cord in vivo . We have also identified a novel endpoint of the dI5 lineage trajectory and found that dIs become more transcriptionally homogenous during terminal differentiation. Together, this study introduces a valuable tool for further discovery about the timing of gene expression during dI differentiation and demonstrates its utility clarifying dI lineage relationships.

Summary statement

Pseudotime analyses of embryonic stem cell-derived dorsal spinal interneurons reveals both novel regulators and lineage relationships between different interneuron populations.

A transcriptomics-based drug repositioning approach to identify drugs with similar activities for the treatment of muscle pathologies in spinal muscular atrophy (SMA) models

Spinal muscular atrophy (SMA) is a genetic neuromuscular disorder caused by the reduction of survival of motor neuron (SMN) protein levels. Although three SMN-augmentation therapies are clinically approved that significantly slow down disease progression, they are unfortunately not cures. Thus, complementary SMN-independent therapies that can target key SMA pathologies and that can support the clinically approved SMN-dependent drugs are the forefront of therapeutic development. We have previously demonstrated that prednisolone, a synthetic glucocorticoid (GC) improved muscle health and survival in severe Smn-/-;SMN2 and intermediate Smn2B/- SMA mice. However, long-term administration of prednisolone can promote myopathy. We thus wanted to identify genes and pathways targeted by prednisolone in skeletal muscle to discover clinically approved drugs that are predicted to emulate prednisolone's activities. Using an RNA-sequencing, bioinformatics, and drug repositioning pipeline on skeletal muscle from symptomatic prednisolone-treated and untreated Smn-/-; SMN2 SMA and Smn+/-; SMN2 healthy mice, we identified molecular targets linked to prednisolone's ameliorative effects and a list of 580 drug candidates with similar predicted activities. Two of these candidates, metformin and oxandrolone, were further investigated in SMA cellular and animal models, which highlighted that these compounds do not have the same ameliorative effects on SMA phenotypes as prednisolone; however, a number of other important drug targets remain. Overall, our work further supports the usefulness of prednisolone's potential as a second-generation therapy for SMA, identifies a list of potential SMA drug treatments and highlights improvements for future transcriptomic-based drug repositioning studies in SMA.

Comparison of secreted miRNAs and proteins during proliferation and differentiation of bovine satellite cells in culture implies potential roles in regulating myogenesis

Cultivated meat is an emerging new technology to produce sustainable meat for the future. The common approach for cultivated meat, is the isolation of satellite cells from donor animals, followed by in vitro proliferation and differentiation into primitive muscle fibers. The transformation of satellite cells into myofibers is tightly orchestrated by intra-cellular signaling, while the inter-cellular signaling is less well understood. Thus, the current study was conducted to map the secretion of potential signaling molecules (MicroRNAs and proteins) during proliferation and differentiation. Primary cultures of satellite cells were grown to 50% and 80% confluence, representing the proliferative phase or serum-starved for 1 and 3 days to induce differentiation. Post incubation in FBS-free media, the media were collected and analyzed for miRNA and protein content using gene-arrays and LC-MS/MS, respectively. When comparing the miRNA secretome at 50% and 80% confluence, we observed four differentially expressed miRNA, while only five were differentially expressed when comparing Day 1 to Day 3. A subsequent in silico analysis suggested that pathways of importance for myogenesis, e.g., MAPK and AMPK signaling, could be regulated by the secreted miRNAs. In addition, >300 proteins were secreted, including insulin-like growth factor 1 binding proteins 2, 3, 4, 5 and 6. In conclusion, this study demonstrated differential secretion of several miRNAs and proteins during both proliferation and differentiation of bovine satellite cells in vitro.

Loss of lysosomal acid lipase results in mitochondrial dysfunction and fiber switch in skeletal muscles of mice

OBJECTIVE

Lysosomal acid lipase (LAL) is the only enzyme known to hydrolyze cholesteryl esters (CE) and triacylglycerols in lysosomes at an acidic pH. Despite the importance of lysosomal hydrolysis in skeletal muscle (SM), research in this area is limited. We hypothesized that LAL may play an important role in SM development, function, and metabolism as a result of lipid and/or carbohydrate metabolism disruptions.

RESULTS

Mice with systemic LAL deficiency (Lal-/-) had markedly lower SM mass, cross-sectional area, and Feret diameter despite unchanged proteolysis or protein synthesis markers in all SM examined. In addition, Lal-/- SM showed increased total cholesterol and CE concentrations, especially during fasting and maturation. Regardless of increased glucose uptake, expression of the slow oxidative fiber marker MYH7 was markedly increased in Lal-/-SM, indicating a fiber switch from glycolytic, fast-twitch fibers to oxidative, slow-twitch fibers. Proteomic analysis of the oxidative and glycolytic parts of the SM confirmed the transition between fast- and slow-twitch fibers, consistent with the decreased Lal-/- muscle size due to the "fiber paradox". Decreased oxidative capacity and ATP concentration were associated with reduced mitochondrial function of Lal-/- SM, particularly affecting oxidative phosphorylation, despite unchanged structure and number of mitochondria. Impairment in muscle function was reflected by increased exhaustion in the treadmill peak effort test in vivo.

CONCLUSION

We conclude that whole-body loss of LAL is associated with a profound remodeling of the muscular phenotype, manifested by fiber type switch and a decline in muscle mass, most likely due to dysfunctional mitochondria and impaired energy metabolism, at least in mice.

Expressions of Insulin-like Growth Factor System among Different Breeds Impact Piglets' Growth during Weaning

The present study investigated the insulin-like growth factors (IGFs) and their receptors and binding proteins among three pig breeds during weaning. Sixty Duroc (DR), Taoyuan black (TYB), and Xiangcun black (XCB) piglets (20 piglets per breed) were selected at 21 and 24 (3 days of post-weaning) days of age to analyze organ indices, plasma concentrations of IGF and IGF-binding proteins (IGFBPs) using ELISA kits, and gene expression of IGF-system-related components in different tissues. The plasma IGFBP-3 concentration in TYB piglets was higher (p > 0.05) than in the XCB and DR piglets at 21 days of age. At 21 days of age, compared with the DR piglets, the IGF-1 expression was lower (p < 0.05) in the kidney, but it was higher (p < 0.05) in the spleen of XCB and TYB piglets. At 24 days of age, the IGF-1 expression was higher (p < 0.05) in the kidney of TYB piglets than in the XCB and DR piglets, while IGFBP-3 in the stomach and IGFBP-4 in the liver of XCB and TYB piglets were lower (p < 0.05) compared with the DR piglets. Weaning down-regulated (p < 0.05) IGF-1 expression in the jejunum, spleen, and liver of piglets, while it up-regulated (p < 0.05) IGFBP-3 expression in the stomach, IGFBP-4 in the liver, IGFBP-5 in the ileum, and IGFBP-6 in the jejunum of DR piglets. Spearman's correlation analysis showed a negative correlation (p < 0.05) between plasma IGFBP-2 and IGFBP-5 concentration and the organ indices of piglets. Collectively, there were significant differences in the IGF system components among the three pig breeds. The IGF system components were altered during weaning, which might be involved in weaning stress to decrease the growth of piglets.

Time-Dependent Changes in Muscle IGF1-IGFBP5-PAPP System after Sciatic Denervation

Denervation-induced muscle atrophy is a frequent cause of skeletal muscle diseases. However, the role of the most important muscle growth factor, insulin-like growth factor (IGF-1), in this process is poorly understood. IGF-1 activity is controlled by six IGF-1 binding proteins (IGFBPs). In skeletal muscle, IGFBP-5 seems to have an important role in atrophic processes. Furthermore, pappalysins (PAPP-A) modulate muscle growth by increasing IGF-1 bioavailability through IGFBP cleavage. We aimed to study the time-dependent changes in the IGF1-IGFBP5-PAPP system and its regulators in gastrocnemius muscle after sciatic denervation. Gastrocnemius atrophy and overexpression of IGF-1 was observed from day 3 post-denervation. The proteolytic factors measured were elevated from day 1 post-denervation onwards. Expression of both IGFBP-5 and pappalysins were increased on days 1 and 3. Subsequently, on days 7 to 14 pappalysins returned to control levels while IGFBP-5 remained elevated. The ratio IGFBP-5/PAPP-A was correlated with the main proteolytic markers. All data suggest that the initial increase of pappalysins could facilitate the IGF-1 action on muscle growth, whereas their subsequent decrease could lead to further muscle wasting.

Desmocollin-1 is associated with pro-metastatic phenotype of luminal A breast cancer cells and is modulated by parthenolide

BACKGROUND

Desmocollin-1 (DSC1) is a desmosomal transmembrane glycoprotein that maintains cell-to-cell adhesion. DSC1 was previously associated with lymph node metastasis of luminal A breast tumors and was found to increase migration and invasion of MCF7 cells in vitro. Therefore, we focused on DSC1 role in cellular and molecular mechanisms in luminal A breast cancer and its possible therapeutic modulation.

METHODS

Western blotting was used to select potential inhibitor decreasing DSC1 protein level in MCF7 cell line. Using atomic force microscopy we evaluated effect of DSC1 overexpression and modulation on cell morphology. The LC-MS/MS analysis of total proteome on Orbitrap Lumos and RNA-Seq analysis of total transcriptome on Illumina NextSeq 500 were performed to study the molecular mechanisms associated with DSC1. Pull-down analysis with LC-MS/MS detection was carried out to uncover DSC1 protein interactome in MCF7 cells.

RESULTS

Analysis of DSC1 protein levels in response to selected inhibitors displays significant DSC1 downregulation (p-value ≤ 0.01) in MCF7 cells treated with NF-κB inhibitor parthenolide. Analysis of mechanic cell properties in response to DSC1 overexpression and parthenolide treatment using atomic force microscopy reveals that DSC1 overexpression reduces height of MCF7 cells and conversely, parthenolide decreases cell stiffness of MCF7 cells overexpressing DSC1. The LC-MS/MS total proteome analysis in data-independent acquisition mode shows a strong connection between DSC1 overexpression and increased levels of proteins LACRT and IGFBP5, increased expression of IGFBP5 is confirmed by RNA-Seq. Pathway analysis of proteomics data uncovers enrichment of proliferative MCM_BIOCARTA pathway including CDK2 and MCM2-7 after DSC1 overexpression. Parthenolide decreases expression of LACRT, IGFBP5 and MCM_BIOCARTA pathway specifically in DSC1 overexpressing cells. Pull-down assay identifies DSC1 interactions with cadherin family proteins including DSG2, CDH1, CDH3 and tyrosine kinase receptors HER2 and HER3; parthenolide modulates DSC1-HER3 interaction.

CONCLUSIONS

Our systems biology data indicate that DSC1 is connected to mechanisms of cell cycle regulation in luminal A breast cancer cells, and can be effectively modulated by parthenolide.

Nutritional status affects Igf1 regulation of skeletal muscle myogenesis, myostatin, and myofibrillar protein degradation pathways in gopher rockfish (Sebastes carnatus)

Insulin-like growth factor-1 (Igf1) regulates skeletal muscle growth in fishes by increasing protein synthesis and promoting muscle hypertrophy. When fish experience periods of insufficient food intake, they undergo slower muscle growth or even muscle wasting, and those changes emerge in part from nutritional modulation of Igf1 signaling. Here, we examined how food deprivation (fasting) modulates Igf1 regulation of liver and skeletal muscle gene expression in gopher rockfish (Sebastes carnatus), a nearshore rockfish of importance for commercial and recreational fisheries in the northeastern Pacific Ocean, to understand how food limitation impacts Igf regulation of muscle growth pathways. Rockfish were either fed or fasted for 14 d, after which a subset of fish from each group was treated with recombinant Igf1 from sea bream (Sparus aurata). Fish that were fasted lost body mass and had lower body condition, reduced hepatosomatic index, and lower plasma Igf1 concentrations, as well as a decreased abundance of igf1 gene transcripts in the liver, increased hepatic mRNAs for Igf binding proteins igfbp1a, igfbp1b, and igfbp3a, and decreased mRNA abundances for igfbp2b and a putative Igf acid labile subunit (igfals) gene. In skeletal muscle, fasted fish showed a reduced abundance of intramuscular igf1 mRNAs but elevated gene transcripts encoding Igf1 receptors A (igf1ra) and B (igf1rb), which also showed downregulation by Igf1. Fasting increased skeletal muscle mRNAs for myogenin and myostatin1, as well as ubiquitin ligase F-box only protein 32 (fbxo32) and muscle RING-finger protein-1 (murf1) genes involved in muscle atrophy, while concurrently downregulating mRNAs for myoblast determination protein 2 (myod2), myostatin2, and myogenic factors 5 (myf5) and 6 (myf6 encoding Mrf4). Treatment with Igf1 downregulated muscle myostatin1 and fbxo32 under both feeding conditions, but showed feeding-dependent effects on murf1, myf5, and myf6/Mrf4 gene expression indicating that Igf1 effects on muscle growth and atrophy pathways is contingent on recent food consumption experience.

Comparative and Functional Analysis of miRNAs and mRNAs Involved in Muscle Fiber Hypertrophy of Juvenile and Adult Goats

MicroRNAs (miRNAs) are small non-coding RNAs that post-transcriptionally regulate several pathway intermediates and affect the skeletal muscle development in mice, pigs, sheep, and cattle. However, to date, only a small number of miRNAs have been reported in the muscle development of goats. In this report, the longissimus dorsi transcripts of one- and ten-month-old goats were analyzed by sequencing RNAs and miRNAs. The results showed that the ten-month-old Longlin goats had 327 up- and 419 down-regulated differentially expressed genes (DEGs) compared with the one-month-old. In addition, 20 co-up-regulated and 55 co-down-regulated miRNAs involved in the muscle fiber hypertrophy of goats were identified in ten-month-old Longlin and Nubian goats compared with one-month-old. Five miRNA-mRNA pairs (chi-let-7b-3p-MIRLET7A, chi-miR193b-3p-MMP14, chi-miR-355-5p-DGAT2, novel_128-LOC102178119, novel_140-SOD3) involved in the goat skeletal muscle development were identified by miRNA-mRNA negative correlation network analysis. Our results provided new insight into the functional roles of goat muscle-associated miRNAs, allowing a deeper understanding of the transformation of miRNA roles during mammalian muscle development.

Evolutionary analysis and functional characterization reveal the role of the insulin-like growth factor system in a diversified selection of chickens (Gallus gallus)

The insulin-like growth factor (IGF) system plays an indispensable role in embryonic and postnatal development in mammals. However, the effects of the system on growth, carcass, and egg-laying traits, and diversified selection have not been systematically studied in chickens. In the present study, firstly the composition and gene structures of the chicken IGF system were investigated using phylogenetic tree and conserved synteny analysis. Then the effects of the genetic variations in the IGF system genes on breeding of specialized varieties were explored by principal component analysis. In addition, the spatiotemporal expression properties of the genes in this system were analyzed by RT-qPCR and the functions of the genes in egg production performance and growth were explored by association study. Moreover, the effects of IGF-binding proteins 3 (IGFBP3) on skeletal muscle development in chicken were investigated by cell cycle analysis, 5-ethynyl-2'-deoxyuridine (EdU) and Cell Counting Kit-8 (CCK-8) assays. The results showed that the chicken IGF system included 13 members which could be classified into 3 groups based on their amino acid sequences: IGF binding proteins 1 to 5 and 7 (IGFBP1-5 and 7) belonged to the first group; IGF 1 and 2 (IGF1 and IGF2), and IGF 1 and 2 receptor (IGF1R and IGF2R) belonged to the second group; and IGF2 binding proteins 1-3 (IGF2BP1-3) belonged to the third group. The IGF2BP1 and 3, and IGFBP2, 3, and 7 genes likely contributed more to the formation of both the specialized meat-type and egg-type lines, whereas IGFBP1 and 5 likely contributed more to the formation of the egg-type lines. The SNPs in the IGF2BP3 and IGFBP2 and 5 genes were significantly associated with egg number, and SNPs in the IGFBP3 promoter region were significantly associated with body weight, breast muscle weight and leg muscle weight. The IGFBP3 inhibited proliferation but promoted differentiation of chicken primary myoblasts (CPMs). These results provide insights into the roles of the IGF system in the diversified selection of chickens. The SNPs associated with egg-laying performance, growth, and carcass traits could be used as genetic markers for breeding selection of chickens in the future.

Pappalysins and Stanniocalcins and Their Relationship With the Peripheral IGF Axis in Newborns and During Development

CONTEXT

Pappalysins (PAPP-A, PAPP-A2) modulate body growth by increasing insulin-like growth factor I (IGF-I) bioavailability through cleavage of insulin-like growth factor binding proteins (IGFBPs) and are inhibited by stanniocalcins (STC1, STC2). Normative data on these novel factors, as well as on free IGF-I and uncleaved fractions of IGFBPs, are not well established.

OBJECTIVE

This work aimed to determine serum concentrations of PAPP-A, PAPP-A2, STC1, and STC2 in relationship with other growth hormone (GH)-IGF axis parameters during development.

METHODS

Full-term newborns (150; gestational age: 39.30 ± 1.10 weeks), 40 preterm newborns (30.87 ± 3.35 weeks), and 1071 healthy individuals (aged 1-30 years) were included in the study and divided according to their Tanner stages (males and females): I:163 males, 154 females; II:100 males, 75 females; III:83 males, 96 females; IV: 77 males, 86 females; and V:109 males,128 females.

RESULTS

Serum concentrations of PAPP-A, PAPP-A2, STC1, STC2, IGFBP-2, total IGFBP-4, and total IGFBP-5 were elevated at birth and declined throughout childhood. In postnatal life, PAPP-A2 concentrations decreased progressively in concomitance with the free/total IGF-I ratio; however, stanniocalcin concentrations remained stable. PAPP-A2 concentrations positively correlated with the free/total IGF-I ratio (r = +0.28; P < .001) and negatively with the intact/total IGFBP-3 ratio (r = -0.23; P < .001). PAPP-A concentrations inversely correlated with intact/total IGFBP-4 ratio (r = -0.21; P < .001), with PAPP-A concentrations being lower in females at all ages. Association studies indicate the importance of stanniocalcins and pappalysins in the control of this axis in an age-specific manner.

CONCLUSION

This study provides reference values of pappalysins and stanniocalcins, which modulate IGF-I activity by changing the concentrations of cleaved and uncleaved IGFBPs.

Alterations in insulin-like growth factor system in spinal muscular atrophy

INTRODUCTION/AIMS

Spinal muscular atrophy (SMA) is an inherited neuromuscular disease caused by survival motor neuron (SMN) protein deficiency. Insulin-like growth factor-I (IGF-I) is a myotrophic and neurotrophic factor that has been reported to be dysregulated in in vivo SMA model systems. However, detailed analyses of the IGF-I system in SMA patients are missing. In this study, we analyzed the components of the IGF-I system in serum and archived skeletal muscle biopsies of SMA patients.

METHODS

Serum IGF-I, IGF binding protein (IGFBP)-3, and IGFBP-5 levels were analyzed in 11 SMA patients and 13 healthy children by immunoradiometric and enzyme-linked immunosorbent assays. The expression of IGF-I, IGF-I receptor, and IGFBP-5 proteins was investigated by immunofluorescence analysis in the archived skeletal muscle biopsies of 9 SMA patients, 6 patients with non-SMA-related neuromuscular disease and atrophic fibers in muscle biopsy, and 4 controls.

RESULTS

A significant decrease in IGF-I levels (mean ± SD: -1.39 ± 1.46 vs. 0.017 ± 0.83, p = 0.02) and increase in IGFBP-5 levels (mean ± SD: 2358.5 ± 1617.4 ng/mL vs. 1003.4 ± 274.3 ng/mL, p=0.03) were detected in serum samples of SMA patients compared to healthy controls. Increased expression of IGF-I, IGF-I receptor, and IGFBP-5 was detected in skeletal muscle biopsies of SMA patients and non-SMA neuromuscular diseases, indicating atrophy-specific alterations in the pathway.

DISCUSSION

Our findings suggested that the components of the IGF-I system are altered in SMA patients at both the systemic and tissue-specific levels.

Liver and muscle-specific effects of phoenixin-20 on the insulin-like growth factor system mRNAs in zebrafish

OBJECTIVE

Phoenixin-20 (Pnx-20) is a bioactive peptide with endocrine-like actions in vertebrates. Recent studies suggest Pnx-20 promotes growth hormone/insulin-like growth factors (Gh/Igf) axis, an important endocrine regulator of growth in mammals and fish.

DESIGN

In this research, we determined whether Pnx-20 affects the different members of the Igf family, its binding proteins and receptors (Igf-system) in zebrafish liver and muscle.

RESULTS

In vivo administration of Pnx-20 downregulated igfs, igf receptors (igfrs) and igf binding protein (igfbp) 5 mRNA expression in the liver of male and female zebrafish at both 1 and 6 h post-intraperitoneal (IP) injection. Interestingly, this effect occurred at a relatively earlier timepoint in female zebrafish suggesting sex-specific differences in Pnx-20 action. Besides, either 6 or 24 h in vitro incubations with Pnx-20 downregulated the expression of all igfs, igfrs and igfbp5 mRNAs (except igf2a) analyzed in a zebrafish liver cell (ZFL) line. Moreover, siRNA-mediated knockdown of Pnx-20 upregulated all Igf-system mRNAs analyzed in ZFL cells. Together, these results (both in vivo and in vitro) revealed a general suppressive action for both endogenous and exogenous Pnx-20 on the hepatic Igf-system of zebrafish. In contrast, a general sex-specific upregulation of the Igf-system mRNAs analyzed was found in the muscle of Pnx-20 injected fish. Future research should explore the sex- and time-differences observed in the present study.

CONCLUSIONS

Collectively, this research shows that Pnx-20 is a tissue-specific regulator of the liver (suppressor) and muscle (stimulant) Igf signaling in both male and female zebrafish.

CircCCDC91 regulates chicken skeletal muscle development by sponging miR-15 family via activating IGF1-PI3K/AKT signaling pathway

Circular RNAs (circRNAs) has been reported in various tissues of animals and associated with multiple biological processes. From our previous sequencing data, we found a novel circRNA, circCCDC91 which was generated from exon 2 to 8 of the CCDC91 gene. We observed that circCCDC91 was differentially expressed in the chicken breast muscle among 4 different embryonic developmental time points (embryonic day 10 [E10], E13, E16, and E19). Therefore, we assumed that circCCDC91 have a potential function in chicken skeletal muscle development. In this study, we firstly verify the annular structure and expression pattern of circCCDC91, and further investigate on whether circCCDC91 could promote chicken skeletal development. Mechanistically, circCCDC91 could absorb miR-15a, miR-15b-5p, and miR-15c-5p to modulate the expression of Insulin receptor substrate1 (IRS1), as well as activate insulin-1ike growth factor 1-phosphatidylinositol 3-kinase/AKT (IGF1-PI3K/AKT) signaling pathway. In addition, circCCDC91 could rescue skeletal muscle atrophy by activating IGF1-PI3K/AKT pathway. Taken together, the findings in this study revealed that the newly identified circCCDC91 promotes myoblasts proliferation and differentiation, and alleviates skeletal muscle atrophy by directly binding to miR-15 family via activating IGF1-PI3K/AKT signaling pathway in chicken.

Mapping and modeling the genomic basis of differential RNA isoform expression at single-cell resolution with LR-Split-seq

The rise in throughput and quality of long-read sequencing should allow unambiguous identification of full-length transcript isoforms. However, its application to single-cell RNA-seq has been limited by throughput and expense. Here we develop and characterize long-read Split-seq (LR-Split-seq), which uses combinatorial barcoding to sequence single cells with long reads. Applied to the C2C12 myogenic system, LR-split-seq associates isoforms to cell types with relative economy and design flexibility. We find widespread evidence of changing isoform expression during differentiation including alternative transcription start sites (TSS) and/or alternative internal exon usage. LR-Split-seq provides an affordable method for identifying cluster-specific isoforms in single cells.

Per1/Per2-Igf2 axis-mediated circadian regulation of myogenic differentiation

Circadian rhythms regulate cell proliferation and differentiation, but circadian control of tissue regeneration remains elusive at the molecular level. Here, we show that proper myoblast differentiation and muscle regeneration are regulated by the circadian master regulators Per1 and Per2. Depletion of Per1 or Per2 suppressed myoblast differentiation in vitro and muscle regeneration in vivo, demonstrating their nonredundant functions. Both Per1 and Per2 were required for the activation of Igf2, an autocrine promoter of myoblast differentiation, accompanied by Per-dependent recruitment of RNA polymerase II, dynamic histone modifications at the Igf2 promoter and enhancer, and the promoter–enhancer interaction. This circadian epigenetic priming created a preferred time window for initiating myoblast differentiation. Consistently, muscle regeneration was faster if initiated at night, when Per1, Per2, and Igf2 were highly expressed compared with morning. This study reveals the circadian timing as a significant factor for effective muscle cell differentiation and regeneration.

Duloxetine improves cancer-associated pain in a mouse model of pancreatic cancer through stimulation of noradrenaline pathway and its antitumor effects

Pancreatic ductal adenocarcinoma (PDAC) is an aggressive cancer with a poor prognosis. Patients with inoperative PDAC require effective chemotherapy and pain control to increase their quality of life. We investigated whether duloxetine, a serotonin-noradrenaline reuptake inhibitor, improves quality of life in a KPPC (LSL-Kras;Trp53;Pdx1-cre) mouse model of PDAC. Six-week-old KPPC mice were orally administered 4 mg/kg/d duloxetine (n = 12); 4 mg/kg/d duloxetine with 0.15 mg/kg/d atipamezole, a synthetic α2 adrenergic receptor antagonist (n = 9); or vehicle water (n = 11). Body weight and food intake were measured daily, and cancer pain was evaluated by the hunching score and mouse grimace scale. At the endpoint, the tumor status, angiogenesis, and immunoinflammatory condition were analyzed. The pain level using the hunching and mouse grimace scale scores improved by duloxetine in KPPC mice (P < 0.01), whereas the scores that had been reduced by duloxetine were elevated by administration of atipamezole. Kaplan-Meier analysis demonstrated that duloxetine-treated mice had significantly prolonged survival (P < 0.05) with delayed appetite loss, cachexia, and body weight loss. Duloxetine inhibited the proliferation of PDAC cells and cancer-associated fibroblasts in vivo with a shift into an antitumor immunoinflammatory condition and the corresponding plasma cytokine levels. The migrative/invasive potentials of PDAC were inhibited by duloxetine in vitro. Meanwhile, atipamezole did not inhibit the antitumor effects of duloxetine in vitro and in vivo. Therefore, our results indicate that duloxetine mainly improves cancer-associated pain by enhancement of the noradrenergic pathway rather than the serotonergic pathway, whereas duloxetine modulates antitumor effects on PDAC without involvement of the noradrenergic pathway.

Integrated Genome-Wide Analysis of MicroRNA Expression Quantitative Trait Loci in Pig Longissimus Dorsi Muscle

Determining mechanisms regulating complex traits in pigs is essential to improve the production efficiency of this globally important protein source. MicroRNAs (miRNAs) are a class of non-coding RNAs known to post-transcriptionally regulate gene expression affecting numerous phenotypes, including those important to the pig industry. To facilitate a more comprehensive understanding of the regulatory mechanisms controlling growth, carcass composition, and meat quality phenotypes in pigs, we integrated miRNA and gene expression data from longissimus dorsi muscle samples with genotypic and phenotypic data from the same animals. We identified 23 miRNA expression Quantitative Trait Loci (miR-eQTL) at the genome-wide level and examined their potential effects on these important production phenotypes through miRNA target prediction, correlation, and colocalization analyses. One miR-eQTL miRNA, miR-874, has target genes that colocalize with phenotypic QTL for 12 production traits across the genome including backfat thickness, dressing percentage, muscle pH at 24 h post-mortem, and cook yield. The results of our study reveal genomic regions underlying variation in miRNA expression and identify miRNAs and genes for future validation of their regulatory effects on traits of economic importance to the global pig industry.

Single-Cell Analysis of the Muscle Stem Cell Hierarchy Identifies Heterotypic Communication Signals Involved in Skeletal Muscle Regeneration

Muscle regeneration relies on the regulation of muscle stem cells (MuSCs) through paracrine signaling interactions. We analyzed muscle regeneration in mice using single-cell RNA sequencing (scRNA-seq) and generated over 34,000 single-cell transcriptomes spanning four time-points. We identified 15 distinct cell types including heterogenous populations of muscle stem and progenitor cells. We resolved a hierarchical map of these myogenic cells by trajectory inference and observed stage-specific regulatory programs within this continuum. Through ligand-receptor interaction analysis, we identified over 100 candidate regeneration-associated paracrine communication pairs between MuSCs and non-myogenic cells. We show that myogenic stem/progenitor cells exhibit heterogeneous expression of multiple Syndecan proteins in cycling myogenic cells, suggesting that Syndecans may coordinate myogenic fate regulation. We performed ligand stimulation in vitro and confirmed that three paracrine factors (FGF2, TGFβ1, and RSPO3) regulate myogenic cell proliferation in a Syndecan-dependent manner. Our study provides a scRNA-seq reference resource to investigate cell communication interactions in muscle regeneration.

Downregulated hypoxia-inducible factor 1α improves myoblast differentiation under hypoxic condition in mouse genioglossus

The treatment of obstructive sleep apnea-hypopnea syndrome targets the narrow anatomic structure of the upper airway (UA) and lacks an effective therapy for UA dilator muscle dysfunction. Long-term hypoxia can cause damage to UA dilator muscles and trigger a vicious cycle. We previously confirmed that hypoxia-inducible factor 1α (HIF-1α) upregulation mediates muscle fatigue in hypoxia condition, but the underlying mechanism remains to be determined. The present study investigated the intrinsic mechanisms and related pathways of HIF-1α that affect myoblast differentiation, with an aim to search for compounds that have protective effects in hypoxic condition. Differentiation of myoblasts was induced under hypoxia, and we found that hypoxia significantly inhibits the differentiation of myoblasts, damages the ultrastructure of mitochondria, and reduces the expression of myogenin, PGC-1β and pAMPKα1. HIF-1α has a negative regulation effect on AMPK. Downregulation of HIF-1α increases the expression of the abovementioned proteins, promotes the differentiation of myoblasts, and protects mitochondrial integrity. In addition, mitochondrial biogenesis occurs during myogenic differentiation. Inhibition of the AMPK pathway inhibits mitochondrial biogenesis, decreases the level of PGC-1β, and increases apoptosis. Resveratrol dimer can reverse the mitochondrial damage induced by AMPK pathway inhibition and decrease myoblast apoptosis. Our results provided a regulatory mechanism for hypoxic injury in genioglossus which may contribute to the pathogenesis and treatment of OSAHS.

The Roles of Insulin-Like Growth Factor Binding Protein Family in Development and Diseases

The insulin-like growth factor (IGF) system comprises ligands of IGF-I/II, IGF receptors (IGFR), IGF binding proteins (IGFBPs), and IGFBP hydrolases. The IGF system plays multiple roles during various disease development as IGFs are widely involved in cell proliferation and differentiation through regulating DNA transcription. Meanwhile, IGFBPs, which are mainly synthesized in the liver, can bind to IGFs and perform two different functions: either inhibition of IGFs by forming inactive compounds with IGF or enhancement of the function of IGFs by strengthening the IGF-IGFR interaction. Interestingly, IGFBPs may have wider functions through IGF-independent mechanisms. Studies have shown that IGFBPs play important roles in cardiovascular disease, tumor progression, fetal growth, and neuro-nutrition. In this review, we emphasize that different IGFBP family members have common or unique functions in numerous diseases; moreover, IGFBPs may serve as biomarkers for disease diagnosis and prediction.

The phosphoinositide 5-phosphatase INPP5K: From gene structure to in vivo functions

INPP5K (Inositol Polyphosphate 5-Phosphatase K, or SKIP (for Skeletal muscle and Kidney enriched Inositol Phosphatase) is a member of the phosphoinositide 5-phosphatases family. Its protein structure is comprised of a N-terminal catalytic domain which hydrolyses both PtdIns(4,5)P2 and PtdIns(3,4,5)P3, followed by a SKICH domain at the C-terminus which is responsible for protein-protein interactions and subcellular localization of INPP5K. Strikingly, INPP5K is mostly concentrated in the endoplasmic reticulum, although it is also detected at the plasma membrane, in the cytosol and the nucleus. Recently, mutations in INPP5K have been detected in patients with a rare form of autosomal recessive congenital muscular dystrophy with cataract, short stature and intellectual disability. INPP5K functions extend from control of insulin signaling, endoplasmic reticulum stress response and structural integrity, myoblast differentiation, cytoskeleton organization, cell adhesion and migration, renal osmoregulation, to cancer. The goal of this review is thus to summarize and comment recent and less recent data in the literature on INPP5K, in particular on the structure, expression, intracellular localization, interactions and functions of this specific member of the 5-phosphatases family.

Cancer-Associated Muscle Wasting-Candidate Mechanisms and Molecular Pathways

Excessive muscle loss is commonly observed in cancer patients and its association with poor prognosis has been well-established. Cancer-associated sarcopenia differs from age-related wasting in that it is not responsive to nutritional intervention and exercise. This is related to its unique pathogenesis, a result of diverse and interconnected mechanisms including inflammation, disordered metabolism, proteolysis and autophagy. There is a growing body of evidence that suggests that the tumor is the driver of muscle wasting by its elaboration of mediators that influence each of these pro-sarcopenic pathways. In this review, evidence for these tumor-derived factors and putative mechanisms for inducing muscle wasting will be reviewed. Potential targets for future research and therapeutic interventions will also be reviewed.

Intermittent fasting from dawn to sunset for four consecutive weeks induces anticancer serum proteome response and improves metabolic syndrome

Metabolic syndrome is characterized by central obesity, insulin resistance, elevated blood pressure, and dyslipidemia. Metabolic syndrome is a significant risk factor for several common cancers (e.g., liver, colorectal, breast, pancreas). Pharmacologic treatments used for the components of the metabolic syndrome appear to be insufficient to control cancer development in subjects with metabolic syndrome. Murine models showed that cancer has the slowest progression when there is no food consumption during the daily activity phase. Intermittent fasting from dawn to sunset is a form of fasting practiced during human activity hours. To test the anticancer effect of intermittent fasting from dawn to sunset in metabolic syndrome, we conducted a pilot study in 14 subjects with metabolic syndrome who fasted (no eating or drinking) from dawn to sunset for more than 14 h daily for four consecutive weeks. We collected serum samples before 4-week intermittent fasting, at the end of 4th week during 4-week intermittent fasting and 1 week after 4-week intermittent fasting. We performed serum proteomic analysis using nano ultra-high performance liquid chromatography-tandem mass spectrometry. We found a significant fold increase in the levels of several tumor suppressor and DNA repair gene protein products (GP)s at the end of 4th week during 4-week intermittent fasting (CALU, INTS6, KIT, CROCC, PIGR), and 1 week after 4-week intermittent fasting (CALU, CALR, IGFBP4, SEMA4B) compared with the levels before 4-week intermittent fasting. We also found a significant reduction in the levels of tumor promoter GPs at the end of 4th week during 4-week intermittent fasting (POLK, CD109, CAMP, NIFK, SRGN), and 1 week after 4-week intermittent fasting (CAMP, PLAC1) compared with the levels before 4-week intermittent fasting. Fasting from dawn to sunset for four weeks also induced an anti-diabetes proteome response by upregulating the key regulatory proteins of insulin signaling at the end of 4th week during 4-week intermittent fasting (VPS8, POLRMT, IGFBP-5) and 1 week after 4-week intermittent fasting (PRKCSH), and an anti-aging proteome response by upregulating H2B histone proteins 1 week after 4-week intermittent fasting. Subjects had a significant reduction in body mass index, waist circumference, and improvement in blood pressure that co-occurred with the anticancer, anti-diabetes, and anti-aging serum proteome response. These findings suggest that intermittent fasting from dawn to sunset actively modulates the respective genes and can be an adjunct treatment in metabolic syndrome. Further studies are needed to test the intermittent fasting from dawn to sunset in the prevention and treatment of metabolic syndrome-induced cancers.

Differential Expression of IGF1, IGFBP5, MSTN, and MYH1 Across Different Age Classes in American Quarter Horses

The objective of this study was to determine the influence of age on expression of insulin-like growth factor 1 (IGF1), insulin-like growth factor binding protein (IGFBP5), myostatin (MSTN), and myosin (MYH1) genes which are related to growth and muscle development in the American Quarter Horse. Thus, horses (n = 10) from weanling, yearling, 2-, 3-, and 10-year-old age classes were sampled and gene expression was assessed by RT-qPCR. ΔC_T was calculated using the hypoxanthine-guanine phosphoribosyltransferase gene as an internal normalizer. The generalized linear model was used to determine differentially expressed genes, by pairwise comparison between ages. Among technical replicates, the coefficient of variation ranged from 1.0 to 5.2% and was lower than the variation observed between biological replicates (2.1-12.9%). IGF1 demonstrated significantly lower expression in the 3-year-old age class than in weanlings and yearlings, but the 10-year-old age class displayed a significantly higher level than 2- and 3-year-old age classes. Expression of IGFBP5 was highest in weanlings compared with all other age classes. Expression of MSTN was significantly higher in weanlings than in other age classes, whereas 10-year-old horses had an intermediate level of expression, but significantly different from yearlings, 2- and 3-year-old fillies. Finally, expression of MYH1 was lower in 2- and 10-year-old horses than in weanlings and yearlings, whereas 3-year-old fillies demonstrated an intermediate level of expression. Differential expression patterns observed in this preliminary study provide insight into the physiological changes occurring throughout the life span of horses. These patterns could also help explain the variation in performance and endurance between individuals at different developmental stages.

Myogenic, genomic and non-genomic influences of the vitamin D axis in skeletal muscle

Despite vitamin D-deficiency clinically presenting with myopathy, muscle weakness and atrophy, the mechanisms by which vitamin D exerts its homeostatic effects upon skeletal muscle remain to be fully established. Recent studies have shown that the receptor by which 1α,25-dihydroxyvitamin D₃ (1,25[OH]₂ D₃ ) exerts its biological actions (ie, the vitamin D receptor, VDR) elicits both genomic and non-genomic effects upon skeletal muscle. The controversy surrounding skeletal muscle VDR mRNA/protein expression in post-natal muscle has been allayed by myriad recent studies, while dynamic expression of VDR throughout myogenesis, and association of higher VDR levels during muscle regeneration/immature muscle cells, suggests a role in myogenesis and perhaps an enrichment of VDR in satellite cells. Accordingly, in vitro studies have demonstrated 1,25(OH)₂ D₃ is anti-proliferative in myoblasts, yet pro-differentiation in latter stages of myogenesis. These effects involve modulation of gene expression (VDR as a transcriptional co-activator controls ~3% of the genome) and post-genomic intracellular signalling for example, via c-Src and alterations to intramuscular calcium homeostasis and proteostasis. The aim of this review is to consider the biomolecular role for the vitamin D/VDR axis in myogenesis, while also exploring global evidence for genomic and non-genomic mechanisms of action for 1,25(OH)₂ D₃ /VDR.

Delayed access to feed alters gene expression associated with hormonal signaling, cellular differentiation, and protein metabolism in muscle of newly hatch chicks

Birds rely solely on utilization of the yolk sac as a means of nutritional support throughout embryogenesis and early post-hatch, before first feeding occurs. Newly hatched broiler (meat-type) chickens are frequently not given immediate access to feed, and this can result in numerous alterations to developmental processes, including those that occur in muscle. The objective of this study was to characterize the gene expression profile of newly hatched chicks' breast muscle with regards to hormonal regulation of growth and metabolism and development and differentiation of muscle tissue, and determine impacts of delayed access to feed on these profiles. Within 3 h of hatch, birds were placed in battery pens and given immediate access to feed (Fed) or delayed access to feed for 48 h (Delayed Fed). Breast muscle collected from male birds at hatch, or 4 h, 1 day (D), 2D, 4D, and 8D after hatch was used for analysis of mRNA expression by reverse transcription-quantitative PCR. Under fully fed conditions, insulin-like growth factor receptor and leptin receptor mRNA expression decreased as birds aged; however, delayed access to feed resulted in prolonged upregulation of these genes so their mRNA levels were higher in Delayed Fed birds at 2D. These expression profiles suggest that delayed feed access alters sensitivity to hormones that may regulate muscle development. Myogenin, a muscle differentiation factor, showed increasing mRNA expression in Fed birds through 2D, after which expression decreased. A similar expression pattern in Delayed Fed birds was deferred until 4D. Levels of myostatin, a negative regulator of muscle growth, increased in Fed birds starting at 2D, while levels in Delayed Fed birds began to increase at 4D. In Fed birds, levels of transcripts for two genes associated with protein catabolism, F-box protein 32 and forkhead box O3, were lower at 2D, while Delayed Fed mRNA levels did not decrease until 4D. Mechanistic target of rapamycin mRNA levels decreased from 1D through 8D in both treatments, except for a transient increase in the Delayed Fed birds between 1D and 2D. These data suggest that within breast muscle, delayed feeding alters hormonal signaling, interrupts tissue differentiation, postpones onset of growth, and may lead to increased protein catabolism. Together, these processes could ultimately contribute to a reduction in proper growth and development of birds not given feed immediately after hatch, and ultimately hinder the long-term potential of muscle accretion in meat type birds.

The metalloproteinase Papp-aa controls epithelial cell quiescence-proliferation transition

Human patients carrying PAPP-A2 inactivating mutations have low bone mineral density. The underlying mechanisms for this reduced calcification are poorly understood. Using a zebrafish model, we report that Papp-aa regulates bone calcification by promoting Ca2+-transporting epithelial cell (ionocyte) quiescence-proliferation transition. Ionocytes, which are normally quiescent, re-enter the cell cycle under low [Ca2+] stress. Genetic deletion of Papp-aa, but not the closely related Papp-ab, abolished ionocyte proliferation and reduced calcified bone mass. Loss of Papp-aa expression or activity resulted in diminished IGF1 receptor-Akt-Tor signaling in ionocytes. Under low Ca2+ stress, Papp-aa cleaved Igfbp5a. Under normal conditions, however, Papp-aa proteinase activity was suppressed and IGFs were sequestered in the IGF/Igfbp complex. Pharmacological disruption of the IGF/Igfbp complex or adding free IGF1 activated IGF signaling and promoted ionocyte proliferation. These findings suggest that Papp-aa-mediated local Igfbp5a cleavage functions as a [Ca2+]-regulated molecular switch linking IGF signaling to bone calcification by stimulating epithelial cell quiescence-proliferation transition under low Ca2+ stress.

Upregulation of Systemic Inflammatory Pathways Following Anterior Cruciate Ligament Injury Relates to Both Cartilage and Muscular Changes: A Pilot Study

In conjunction with cartilage breakdown, muscle maladaptation including atrophy and increased fibrosis have been observed in the quadriceps following anterior cruciate ligament (ACL) injury. Previously observed upregulated muscle-related proteins in the synovial fluid following ACL rupture allude to cellular communication between the joint and muscle. Therefore, the purpose of this study was to determine whether muscle-related analytes are differentially expressed in the serum. Sixteen patients with an acute ACL tear participated in this IRB-approved study. Serum was obtained at two different time points at a mean of 6 and 14 days post-injury, and serum was analyzed by a highly multiplexed assay of 1,300 proteins. Pathway analysis using DAVID was performed; genes included met three criteria: significant change between the two study time points using a paired t test, significant change between the two study time points using a Mann-Whitney non-parametric test, and significant Benjamini post hoc analysis. Twelve analytes significantly increased between time points. Proteins chitinase-3-like protein 1 (p = 0.01), insulin-like growth factor binding protein 1 (p = 0.01), insulin-like growth factor binding protein 5 (p = 0.02), renin (p = 0.004), and lymphotoxin alpha 1: beta 2 (p = 0.03) were significantly upregulated in serum following acute ACL injury. The current results confirm the inflammatory pattern previously seen in the synovial fluid thought to play a role in the progression of post-traumatic osteoarthritis after ACL injury, and this data also provides further insights into important communication between the joint and quadriceps group, whose function is important in long term health. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 38:387-392, 2020.

Insulin-Like Growth Factor Binding Protein-5 in Physiology and Disease

Insulin-like growth factor (IGF) signaling is regulated by a conserved family of IGF binding proteins (IGFBPs) in vertebrates. Among the six distinct types of IGFBPs, IGFBP-5 is the most highly conserved across species and has the broadest range of biological activities. IGFBP-5 is expressed in diverse cell types, and its expression level is regulated by a variety of signaling pathways in different contexts. IGFBP-5 can exert a range of biological actions including prolonging the half-life of IGFs in the circulation, inhibition of IGF signaling by competing with the IGF-1 receptor for ligand binding, concentrating IGFs in certain cells and tissues, and potentiation of IGF signaling by delivery of IGFs to the IGF-1 receptor. IGFBP-5 also has IGF-independent activities and is even detected in the nucleus. Its broad biological activities make IGFBP-5 an excellent representative for understanding IGFBP functions. Despite its evolutionary conservation and numerous biological activities, knockout of IGFBP-5 in mice produced only a negligible phenotype. Recent research has begun to explain this paradox by demonstrating cell type-specific and physiological/pathological context-dependent roles for IGFBP-5. In this review, we survey and discuss what is currently known about IGFBP-5 in normal physiology and human disease. Based on recent in vivo genetic evidence, we suggest that IGFBP-5 is a multifunctional protein with the ability to act as a molecular switch to conditionally regulate IGF signaling.

The Insulin/IGF System in Mammalian Sexual Development and Reproduction

Persistent research over the past few decades has clearly established that the insulin-like family of growth factors, which is composed of insulin and insulin-like growth factors 1 (IGF1) and 2 (IGF2), plays essential roles in sexual development and reproduction of both males and females. Within the male and female reproductive organs, ligands of the family act in an autocrine/paracrine manner, in order to guide different aspects of gonadogenesis, sex determination, sex-specific development or reproductive performance. Although our knowledge has greatly improved over the last years, there are still several facets that remain to be deciphered. In this review, we first briefly outline the principles of sexual development and insulin/IGF signaling, and then present our current knowledge, both in rodents and humans, about the involvement of insulin/IGFs in sexual development and reproductive functions. We conclude by highlighting some interesting remarks and delineating certain unanswered questions that need to be addressed in future studies.

Interactions of long-term food ration variation and short-term fasting on insulin-like growth factor-1 (IGF-1) pathways in copper rockfish (Sebastes caurinus)

Variation in food intake affects somatic growth by altering the expression of hormones in the somatotropic endocrine axis including insulin-like growth factor-1 (IGF-1). Here, we examined IGF-1 pathway responses to long- and short-term variation in food availability in copper rockfish (Sebastes caurinus), a nearshore Pacific rockfish important for commercial and recreational fisheries. Juvenile copper rockfish were raised under differing ration amounts (3% or 9% mass feed·g^-1 fish wet mass·day^-1) for 140 d to simulate 'long-term' feeding variation, after which some fish from both rations were fasted for 12 d to generate 'short-term' conditions of food deprivation. Rockfish on the 9% ration treatment grew more quickly than those on the 3% ration and were larger in mass, length, and body condition (k) after 152 d. Fish on the 9% ration had higher blood glucose than those on the 3% ration, with fasting decreasing blood glucose in both ration treatments, indicating that both long-term and short-term feed treatments altered energy status. Plasma IGF-1 was higher in rockfish from the 9% ration than those in the 3% ration and was also higher in fed fish than fasted fish. Additionally, plasma IGF-1 related positively to individual variation in specific growth rate (SGR). The positive association between IGF-1 and SGR showed discordance in fish that had experienced different levels of food and growth over the long-term but not short-term, suggesting that long-term nutritional experience can influence the relationship between IGF-1 and growth in this species. Rockfish on the 3% ration showed a lower relative abundance of gene transcripts encoding igf1 in the liver, but higher hepatic mRNAs for IGF binding proteins igfbp1a and igfbp1b. Fasting similarly decreased the abundance of igf1 mRNAs in the liver of fish reared under both the 9% and 3% rations, while concurrently increasing mRNAs encoding the IGF binding proteins igfbp1a, -1b, and -3a. Hepatic mRNAs for igfbp2b, -5a, and -5b were lower with long-term ration variation (3% ration) and fasting. Fish that experienced long-term reduced rations also had higher mRNA levels for igfbp3a, -3b, and IGF receptors isoforms A (igf1rA) and B (igf1rB) in skeletal muscle, but lower mRNA levels for igf1. Fasting increased muscle mRNA abundance for igfbp3a, igf1rA, and igf1rB, and decreased levels for igfbp2a and igf1. These data show that a positive relationship between circulating IGF-1 and individual growth rate is maintained in copper rockfish even when that growth variation relates to differences in food consumption across varying time scales, but that long- and short-term variation in food quantity can shift basal concentrations of circulating IGF-1 in this species.

IGFBP5 suppresses oleate-induced intramyocellular lipids deposition and enhances insulin signaling

Excess intramyocellular lipids are often accompanied by muscle insulin resistance (IR) and type 2 diabetes. The mechanism of the formation of intramyocellular lipids is unclear yet. In this study, we optimized the cellular model of intramyocellular lipids from differentiated C2C12 cells and identified that the expression of insulin-like growth factor-binding protein 5 (IGFBP5) is diminished in this process. Then, we added exogenous recombinant IGFBP5 during myocyte triglyceride (TAG) formation and found decreased lipids accumulation. In addition, IGFBP5 could promote lipolysis when added to the cellular model after the formation of intramyocellular lipids. Moreover, IGFBP5 could enhance myocyte insulin sensitivity by inhibiting the expression of the thioredoxin-interacting protein (TXNIP) and arrestin domain-containing 4 (ARRDC4), which are a negative regulator of insulin signaling in both cases. Meanwhile, IGFBP5 also inhibited the expression of glycerol-3-phosphate acyltransferase (GPAM) and diglyceride acyltransferase 2 (DGAT2), which were involved in TAG synthesis from a fatty acid. IGFBP5 also reduced TAG storage by promoting lipolysis. Therefore, IGFBP5 may play a role in the excess accumulation of lipid in muscle cells of diabetic patients and serve as a reference for further research and treatment of muscle IR and diabetes.

Effects of long-term feeding of rapeseed meal on skeletal muscle transcriptome, production efficiency and meat quality traits in Norwegian Landrace growing-finishing pigs

This study was performed to investigate the effects of dietary inclusion of 20% rapeseed meal (RSM) as an alternative to soybean meal (SBM) in a three-month feeding experiment with growing finishing pigs. Dietary alteration affected growth performance, several carcass traits and transcriptional responses in the skeletal muscle, but did not affect measured meat quality traits. In general, pigs fed the RSM test diet exhibited reduced growth performance compared to pigs on SBM control diet. Significant transcriptional changes in the skeletal muscle of growing pigs fed RSM diet were likely the consequence of an increased amount of fiber and higher polyunsaturated fatty acids, and presence of bioactive phytochemicals, such as glucosinolates. RNAseq pipeline using Tophat2-Cuffdiff identified 57 upregulated and 63 downregulated genes in RSM compared to SBM pigs. Significantly enriched among downregulated pathways was p53-mediated signalling involved in cellular proliferation, while activation of negative growth regulators (IER5, KLF10, BTG2, KLF11, RETREG1, PRUNE2) in RSM fed pigs provided further evidence for reduced proliferation and increased cellular death, in accordance with the observed reduction in performance traits. Upregulation of well-known metabolic controllers (PDK4, UCP3, ESRRG and ESRRB), involved in energy homeostasis (glucose and lipid metabolism, and mitochondrial function), suggested less available energy and nutrients in RSM pigs. Furthermore, several genes supported more pronounced proteolysis (ABTB1, OTUD1, PADI2, SPP1) and reduced protein synthesis (THBS1, HSF4, AP1S2) in RSM muscle tissue. In parallel, higher levels of NR4A3, PDK4 and FGF21, and a drop in adropin, ELOVL6 and CIDEC/FSP27 indicated increased lipolysis and fatty acid oxidation, reflective of lower dressing percentage. Finally, pigs exposed to RSM showed greater expression level of genes responsive to oxidative stress, indicated by upregulation of GPX1, GPX2, and TXNIP.

RSRC1 mutation affects intellect and behaviour through aberrant splicing and transcription, downregulating IGFBP3

RSRC1, whose polymorphism is associated with altered brain function in schizophrenia, is a member of the serine and arginine rich-related protein family. Through homozygosity mapping and whole exome sequencing we show that RSRC1 mutation causes an autosomal recessive syndrome of intellectual disability, aberrant behaviour, hypotonia and mild facial dysmorphism with normal brain MRI. Further, we show that RSRC1 is ubiquitously expressed, and that the RSRC1 mutation triggers nonsense-mediated mRNA decay of the RSRC1 transcript in patients' fibroblasts. Short hairpin RNA (shRNA)-mediated lentiviral silencing and overexpression of RSRC1 in SH-SY5Y cells demonstrated that RSRC1 has a role in alternative splicing and transcription regulation. Transcriptome profiling of RSRC1-silenced cells unravelled specific differentially expressed genes previously associated with intellectual disability, hypotonia and schizophrenia, relevant to the disease phenotype. Protein-protein interaction network modelling suggested possible intermediate interactions by which RSRC1 affects gene-specific differential expression. Patient-derived induced pluripotent stem cells, differentiated into neural progenitor cells, showed expression dynamics similar to the RSRC1-silenced SH-SY5Y model. Notably, patient neural progenitor cells had 9.6-fold downregulated expression of IGFBP3, whose brain expression is affected by MECP2, aberrant in Rett syndrome. Interestingly, Igfbp3-null mice have behavioural impairment, abnormal synaptic function and monoaminergic neurotransmission, likely correlating with the disease phenotype.

Temperature Affects Musculoskeletal Development and Muscle Lipid Metabolism of Gilthead Sea Bream (Sparus aurata)

World population is expected to increase to approximately 9 thousand million people by 2050 with a consequent food security decline. Besides, climate change is a major challenge that humanity is facing, with a predicted rise in mean sea surface temperature of more than 2°C during this century. This study aims to determine whether a rearing temperature of 19, 24, or 28°C may influence musculoskeletal development and muscle lipid metabolism in gilthead sea bream juveniles. The expression of growth hormone (GH)/insulin-like growth factors (IGFs) system-, osteogenic-, myogenic-, and lipid metabolism-related genes in bone and/or white muscle of treated fish, and the in vitro viability, mineralization, and osteogenic genes expression in primary cultured cells derived from bone of the same fish were analyzed. The highest temperature significantly down-regulated igf-1, igf-2, the receptor igf-1ra, and the binding proteins igfbp-4 and igfbp-5b in bone, and in muscle, igf-1 and igf-1ra, suggesting impaired musculoskeletal development. Concerning myogenic factors expression, contrary responses were observed, since the increase to 24°C significantly down-regulated myod1 and mrf4, while at 28°C myod2 and myogenin were significantly up-regulated. Moreover, in the muscle tissue, the expression of the fatty acid transporters cd36 and fabp11, and the lipases lipa and lpl-lk resulted significantly increased at elevated temperatures, whereas β-oxidation markers cpt1a and cpt1b were significantly reduced. Regarding the primary cultured bone-derived cells, a significant up-regulation of the extracellular matrix proteins on, op, and ocn expression was found with increased temperatures, together with a gradual decrease in mineralization along with fish rearing temperature. Overall, these results suggest that increasing water temperature in this species appears to induce unfavorable growth and development of bone and muscle, through modulating the expression of different members of the GH/IGFs axis, myogenic and osteogenic genes, while accelerating the utilization of lipids as an energy source, although less efficiently than at optimal temperatures.

Insulin-like Growth Factor II: An Essential Adult Stem Cell Niche Constituent in Brain and Intestine

Tissue-specific stem cells have unique properties and growth requirements, but a small set of juxtacrine and paracrine signals have been identified that are required across multiple niches. Whereas insulin-like growth factor II (IGF-II) is necessary for prenatal growth, its role in adult stem cell physiology is largely unknown. We show that loss of Igf2 in adult mice resulted in a ∼50% reduction in slowly dividing, label-retaining cells in the two regions of the brain that harbor neural stem cells. Concordantly, induced Igf2 deletion increased newly generated neurons in the olfactory bulb accompanied by hyposmia, and caused impairments in learning and memory and increased anxiety. Induced Igf2 deletion also resulted in rapid loss of stem and progenitor cells in the crypts of Lieberkühn, leading to body-weight loss and lethality and the inability to produce organoids in vitro. These data demonstrate that IGF-II is critical for multiple adult stem cell niches.

Ca2+ concentration-dependent premature death of igfbp5a-/- fish reveals a critical role of IGF signaling in adaptive epithelial growth

The phenotype gap is a challenge for genetically dissecting redundant endocrine signaling pathways, such as the six isoforms in the insulin-like growth factor binding protein (IGFBP) family. Although overexpressed IGFBPs can inhibit or potentiate IGF actions or have IGF-independent actions, mutant mice lacking IGFBP-encoding genes do not exhibit major phenotypes. We found that although zebrafish deficient in igfbp5a did not show overt phenotypes when raised in Ca²⁺-rich solutions, they died prematurely in low Ca²⁺ conditions. A group of epithelial cells expressing igfbp5a take up Ca²⁺ and proliferate under low Ca²⁺ conditions because of activation of IGF signaling. Deletion of igfbp5a blunted low Ca²⁺ stress-induced IGF signaling and impaired adaptive proliferation. Reintroducing zebrafish Igfbp5a, but not its ligand binding-deficient mutant, restored adaptive proliferation. Similarly, adaptive proliferation was restored in zebrafish lacking igfbp5a by expression of human IGFBP5, but not two cancer-associated IGFBP5 mutants. Knockdown of IGFBP5 in human colon carcinoma cells resulted in reduced IGF-stimulated cell proliferation. These results reveal a conserved mechanism by which a locally expressed Igfbp regulates organismal Ca²⁺ homeostasis and survival by activating IGF signaling in epithelial cells and promoting their proliferation in Ca²⁺-deficient states. These findings underscore the importance of physiological context when analyzing loss-of-function phenotypes of endocrine factors.

Role of IGF-binding proteins in regulating IGF responses to changes in metabolism

The IGF-binding protein family contains six members that share significant structural homology. Their principal function is to regulate the actions of IGF1 and IGF2. These proteins are present in plasma and extracellular fluids and regulate access of both IGF1 and II to the type I IGF receptor. Additionally, they have functions that are independent of their ability to bind IGFs. Each protein is regulated independently of IGF1 and IGF2, and this provides an important mechanism by which other hormones and physiologic variables can regulate IGF actions indirectly. Several members of the family are sensitive to changes in intermediary metabolism. Specifically the presence of obesity/insulin resistance can significantly alter the expression of these proteins. Similarly changes in nutrition or catabolism can alter their synthesis and degradation. Multiple hormones such as glucocorticoids, androgens, estrogen and insulin regulate IGFBP synthesis and bioavailability. In addition to their ability to regulate IGF access to receptors these proteins can bind to distinct cell surface proteins or proteins in extracellular matrix and several cellular functions are influenced by these interactions. IGFBPs can be transported intracellularly and interact with nuclear proteins to alter cellular physiology. In pathophysiologic states, there is significant dysregulation between the changes in IGFBP synthesis and bioavailability and changes in IGF1 and IGF2. These discordant changes can lead to marked alterations in IGF action. Although binding protein physiology and pathophysiology are complex, experimental results have provided an important avenue for understanding how IGF actions are regulated in a variety of physiologic and pathophysiologic conditions.

IGF-Binding Proteins: Why Do They Exist and Why Are There So Many?

Insulin-like growth factors (IGFs) are key growth-promoting peptides that act as both endocrine hormones and autocrine/paracrine growth factors. In the bloodstream and in local tissues, most IGF molecules are bound by one of the members of the IGF-binding protein (IGFBP) family, of which six distinct types exist. These proteins bind to IGF with an equal or greater affinity than the IGF1 receptor and are thus in a key position to regulate IGF signaling globally and locally. Binding to an IGFBP increases the half-life of IGF in the circulation and blocks its potential binding to the insulin receptor. In addition to these classical roles, IGFBPs have been shown to modulate IGF signaling locally under various conditions. Although members of the IGFBP family share significant sequence homology, they each have unique structural features and play distinct roles. These IGFBP genes also have different modes of regulation and distinct expression patterns. Some IGFBPs have been found to bind to their own receptors or to translocate into the interior compartments of cells where they may execute IGF-independent actions. In spite of this functional and regulatory diversity, it has been puzzling that loss-of-function studies have yielded relatively little information about the physiological functions of IGFBPs. In this review, we suggest that evolution has tended to retain an array of IGFBPs in order to facilitate fine-tuning of IGF signaling. We explore the emerging explanation that many IGFBP functions have evolved to allow the targeted adjustment of IGF signaling under stressful or irregular conditions, which would likely not be revealed in a standard laboratory setting.