Glycosphingolipid biosynthesis during myogenesis of rat L6 cells in vitro

Distinct microbial assemblages associated with genetic selection for high- and low- muscle yield in rainbow trout

Background

Fish gut microbial assemblages play a crucial role in the growth rate, metabolism, and immunity of the host. We hypothesized that the gut microbiota of rainbow trout was correlated with breeding program based genetic selection for muscle yield. To test this hypothesis, fecal samples from 19 fish representing an F2 high-muscle genetic line (ARS-FY-H) and 20 fish representing an F1 low-muscle yield genetic line (ARS-FY-L) were chosen for microbiota profiling using the 16S rRNA gene. Significant differences in microbial assemblages between these two genetic lines might represent the effect of host genetic selection in structuring the gut microbiota of the host.

Results

Tukey’s transformed inverse Simpson indices indicated that high muscle yield genetic line (ARS-FY-H) samples have higher microbial diversity compared to those of the low muscle yield genetic line (ARS-FY-L) (LMM, χ2(1) =14.11, p < 0.05). The fecal samples showed statistically distinct structure in microbial assemblages between the genetic lines (F_1,36 = 4.7, p < 0.05, R² = 11.9%). Functional profiling of bacterial operational taxonomic units predicted characteristic functional capabilities of the microbial communities in the high (ARS-FY-H) and low (ARS-FY-L) muscle yield genetic line samples.

Conclusion

The significant differences of the microbial assemblages between high (ARS-FY-H) and low (ARS-FY-L) muscle yield genetic lines indicate a possible effect of genetic selection on the microbial diversity of the host. The functional composition of taxa demonstrates a correlation between bacteria and improving the muscle accretion in the host, probably, by producing various metabolites and enzymes that might aid in digestion. Further research is required to elucidate the mechanisms involved in shaping the microbial community through host genetic selection.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-020-07204-7.

Systemic Actions of Breast Cancer Facilitate Functional Limitations

Breast cancer is a disease of a specific organ, but its effects are felt throughout the body. The systemic effects of breast cancer can lead to functional limitations in patients who suffer from muscle weakness, fatigue, pain, fibromyalgia, or many other dysfunctions, which hasten cancer-associated death. Mechanistic studies have identified quite a few molecular defects in skeletal muscles that are associated with functional limitations in breast cancer. These include circulating cytokines such as TNF-α, IL-1, IL-6, and TGF-β altering the levels or function of myogenic molecules including PAX7, MyoD, and microRNAs through transcriptional regulators such as NF-κB, STAT3, and SMADs. Molecular defects in breast cancer may also include reduced muscle mitochondrial content and increased extracellular matrix deposition leading to energy imbalance and skeletal muscle fibrosis. This review highlights recent evidence that breast cancer-associated molecular defects mechanistically contribute to functional limitations and further provides insights into therapeutic interventions in managing functional limitations, which in turn may help to improve quality of life in breast cancer patients.

Linking Cancer Cachexia-Induced Anabolic Resistance to Skeletal Muscle Oxidative Metabolism

Cancer cachexia, a wasting syndrome characterized by skeletal muscle depletion, contributes to increased patient morbidity and mortality. While the intricate balance between protein synthesis and breakdown regulates skeletal muscle mass, the suppression of basal protein synthesis may not account for the severe wasting induced by cancer. Therefore, recent research has shifted to the regulation of “anabolic resistance,” which is the impaired ability of nutrition and exercise to stimulate protein synthesis. Emerging evidence suggests that oxidative metabolism can regulate both basal and induced muscle protein synthesis. While disrupted protein turnover and oxidative metabolism in cachectic muscle have been examined independently, evidence suggests a linkage between these processes for the regulation of cancer-induced wasting. The primary objective of this review is to highlight the connection between dysfunctional oxidative metabolism and cancer-induced anabolic resistance in skeletal muscle. First, we review oxidative metabolism regulation of muscle protein synthesis. Second, we describe cancer-induced alterations in the response to an anabolic stimulus. Finally, we review a role for exercise to inhibit cancer-induced anabolic suppression and mitochondrial dysfunction.

Lipid modulation of skeletal muscle mass and function

Loss of skeletal muscle mass is a characteristic feature of various pathologies including cancer, diabetes, and obesity, as well as being a general feature of ageing. However, the processes underlying its pathogenesis are not fully understood and may involve multiple factors. Importantly, there is growing evidence which supports a role for fatty acids and their derived lipid intermediates in the regulation of skeletal muscle mass and function. In this review, we discuss evidence pertaining to those pathways which are involved in the reduction, increase and/or preservation of skeletal muscle mass by such lipids under various pathological conditions, and highlight studies investigating how these processes may be influenced by dietary supplementation as well as genetic and/or pharmacological intervention.

Altered microRNA expression in bovine skeletal muscle with age

Age-dependent decline in skeletal muscle function leads to several inherited and acquired muscular disorders in elderly individuals. The levels of microRNAs (miRNAs) could be altered during muscle maintenance and repair. We therefore performed a comprehensive investigation for miRNAs from five different periods of bovine skeletal muscle development using next-generation small RNA sequencing. In total, 511 miRNAs, including one putatively novel miRNA, were identified. Thirty-six miRNAs were differentially expressed between prenatal and postnatal stages of muscle development including several myomiRs (miR-1, miR-206 and let-7 families). Compared with miRNA expression between different muscle tissues, 14 miRNAs were up-regulated and 22 miRNAs were down-regulated in the muscle of postnatal stage. In addition, a novel miRNA was predicted and submitted to the miRBase database as bta-mir-10020. A dual luciferase reporter assay was used to demonstrate that bta-mir-10020 directly targeted the 3'-UTR of the bovine ANGPT1 gene. The overexpression of bta-mir-10020 significantly decreased the DsRed fluorescence in the wild-type expression cassette compared to the mutant type. Using three computational approaches - miranda, pita and rnahybrid - these differentially expressed miRNAs were also predicted to target 3609 bovine genes. Disease and biological function analyses and the KEGG pathway analysis revealed that these targets were statistically enriched in functionality for muscle growth and disease. Our miRNA expression analysis findings from different states of muscle development and aging significantly expand the repertoire of bovine miRNAs now shown to be expressed in muscle and could contribute to further studies on growth and developmental disorders in this tissue type.

A role for Galgt1 in skeletal muscle regeneration

BACKGROUND

Cell surface glycans are known to play vital roles in muscle membrane stability and muscle disease, but to date, roles for glycans in muscle regeneration have been less well understood. Here, we describe a role for complex gangliosides synthesized by the Galgt1 gene in muscle regeneration.

METHODS

Cardiotoxin-injected wild type (WT) and Galgt1 (-/-) muscles, and mdx and Galgt1 (-/-) mdx muscles, were used to study regeneration in response to acute and chronic injury, respectively. Muscle tissue was analyzed at various time points for morphometric measurements and for gene expression changes in satellite cell and muscle differentiation markers by quantitative real-time polymerase chain reaction (qRT-PCR). Primary cell cultures were used to measure growth rate and myotube formation and to identify Galgt1 expression changes after cardiotoxin by fluorescence-activated cell sorting (FACS). Primary cell culture and tissue sections were also used to quantify satellite cell apoptosis.

RESULTS

A query of a microarray data set of cardiotoxin-induced mouse muscle gene expression changes identified Galgt1 as the most upregulated glycosylation gene immediately after muscle injury. This was validated by qRT-PCR as a 23-fold upregulation in Galgt1 expression 1 day after cardiotoxin administration and a 16-fold upregulation in 6-week-old mdx muscles. These changes correlated with increased expression of Galgt1 protein and GM1 ganglioside in mononuclear muscle cells. In the absence of Galgt1, cardiotoxin-induced injury led to significantly reduced myofiber diameters after 14 and 28 days of regeneration. Myofiber diameters were also significantly reduced in Galgt1-deficient mdx mice compared to age-matched mdx controls, and this was coupled with a significant increase in the loss of muscle tissue. Cardiotoxin-injected Galgt1 (-/-) muscles showed reduced gene expression of the satellite cell marker Pax7 and increased expression of myoblast markers MyoD, Myf5, and Myogenin after injury along with a tenfold increase in apoptosis of Pax7-positive muscle cells. Cultured primary Galgt1 (-/-) muscle cells showed a normal growth rate but demonstrated premature fusion into myofibers, resulting in an overall impairment of myofiber formation coupled with a threefold increase in muscle cell apoptosis.

CONCLUSIONS

These experiments demonstrate a role for Galgt1 in skeletal muscle regeneration and suggest that complex gangliosides made by Galgt1 modulate the survival and differentiation of satellite cells.

Implications for the mammalian sialidases in the physiopathology of skeletal muscle

The family of mammalian sialidases is composed of four distinct versatile enzymes that remove negatively charged terminal sialic acid residues from gangliosides and glycoproteins in different subcellular areas and organelles, including lysosomes, cytosol, plasma membrane and mitochondria. In this review we summarize the growing body of data describing the important role of sialidases in skeletal muscle, a complex apparatus involved in numerous key functions and whose functional integrity can be affected by various conditions, such as aging, chronic diseases, cancer and neuromuscular disorders. In addition to supporting the proper catabolism of glycoconjugates, sialidases can affect different signaling pathways by desialylation of many receptors and modulation of ganglioside content in cell membranes, thus actively participating in myoblast proliferation, differentiation and hypertrophy, insulin responsiveness and skeletal muscle architecture.

Ganglioside GM3 levels are altered in a mouse model of HIBM: GM3 as a cellular marker of the disease

Objective

HIBM (Hereditary Inclusion Body Myopathy) is a recessive hereditary disease characterized by adult-onset, slowly progressive muscle weakness sparing the quadriceps. It is caused by a single missense mutation of each allele of the UDP-N-acetylglucosamine 2-epimerase/N-acetylmannosamine kinase (GNE) gene, a bifunctional enzyme catalyzing the first two steps of sialic acid synthesis in mammals. However, the mechanisms and cellular pathways affected by the GNE mutation and causing the muscle weakness could not be identified so far. Based on recent evidence in literature, we investigated a new hypothesis, i.e. the involvement in the disease of the GM3 ganglioside, a specific glycolipid implicated in muscle cell proliferation and differentiation.

Methods

qRT-PCR analysis of St3gal5 (GM3 synthase) gene expression and HPLC quantification of GM3 ganglioside were conducted on muscle tissue from a mouse model of HIBM harboring the M712T mutation of GNE (Gne^M712T/M712T mouse) vs control mice (Gne^+/+ mouse).

Results

St3gal5 mRNA levels were significantly lower in Gne^M712T/M712T mouse muscles vs Gne^+/+ mouse muscles (64.41%±10% of Gne^+/+ levels). GM3 ganglioside levels showed also a significant decrease in Gne^M712T/M712T mouse muscle compared to Gne^+/+ mouse muscle (18.09%±5.33% of Gne^+/+ levels). Although these Gne^M712T/M712T mice were described to suffer severe glomerular proteinuria, no GM3 alterations were noted in kidneys, highlighting a tissue specific alteration of gangliosides.

Conclusion

The M712T mutation of GNE hampers the muscle ability to synthesize normal levels of GM3. This is the first time that a mutation of GNE can be related to the molecular pathological mechanism of HIBM.

NEU3 sialidase strictly modulates GM3 levels in skeletal myoblasts C2C12 thus favoring their differentiation and protecting them from apoptosis

Membrane-bound sialidase NEU3, often referred to as the "ganglioside sialidase," has a critical regulatory function on the sialoglycosphingolipid pattern of the cell membrane, with an anti-apoptotic function, especially in cancer cells. Although other sialidases have been shown to be involved in skeletal muscle differentiation, the role of NEU3 had yet to be disclosed. Herein we report that NEU3 plays a key role in skeletal muscle differentiation by strictly modulating the ganglioside content of adjacent cells, with special regard to GM3. Induced down-regulation of NEU3 in murine C2C12 myoblasts, even when partial, totally inhibits their capability to differentiate by increasing the GM3 level above a critical point, which causes epidermal growth factor receptor inhibition (and ultimately its down-regulation) and an higher responsiveness of myoblasts to the apoptotic stimuli.

Overexpression of cytosolic sialidase Neu2 induces myoblast differentiation in C2C12 cells

Cytosolic sialidase Neu2 has been implicated in myoblast differentiation. Here we observed a significant upregulation of Neu2 expression during differentiation of murine C2C12 myoblasts. This was evidenced both as an increase in Neu2 mRNA steady-state levels and in the cytosolic sialidase enzymatic activity. To understand the biological significance of Neu2 upregulation in myoblast differentiation, C2C12 cells were stably transfected with the rat cytosolic sialidase Neu2 cDNA. Neu2 overexpressing clones were characterized by a marked decrement of cell proliferation and by the capacity to undergo spontaneous myoblast differentiation also when maintained under standard growth conditions. This was evidenced by the formation of myogenin-positive myotubes and by a significant decrease in the nuclear levels of cyclin D1 protein. No differentiation was on the contrary observed in parental and mock-transfected cells under the same experimental conditions. The results indicate that Neu2 upregulation per se is sufficient to trigger myoblast differentiation in C2C12 cells.

Glycosphingolipids of skeletal muscle: I. Subcellular distribution of neutral glycosphingolipids and gangliosides in rabbit skeletal muscle

Membrane vesicles were prepared from rabbit skeletal muscle, separated by sucrose density gradient centrifugation and characterized by their specific marker enzymes, ligand binding, and ion flux activities. The fractions obtained (in the order of increasing density) were sarcolemma (SL), T-tubules (TT), sarcoplasmic reticulum (SR1 and SR2) and triads/mitochondria (Tr/M). Their glycosphingolipid compositions were analyzed by biochemical and immunochemical methods with specific antibodies (TLC immunostaining) and characteristic patterns were obtained from respective membrane fractions, expressed on a protein basis. Glucosylceramide, the main neutral glycosphingolipid of rabbit muscle, was found in SL and TT fractions, whereas SR and Tr/M vesicles lack this compound. Lactosylceramide was selectively recovered in the SR1 fraction. GM3(Neu5Ac), the main ganglioside in rabbit muscle, was found to account for 64% in the SL, 13% in the TT, 7% in the SR1, 3% in the SR2 and 13% in the Tr/M fractions. IV3Neu5Ac-nLcOse4Cer was mostly abundant in SL and decreased in the order SL > TT, Tr/M > SR1, SR2. IV6Neu5Ac-nLcOse4Cer was only detected in the SL and Tr/M fractions in noteworthy quantities. Ganglioseries gangliosides GM1, GD1a, GD1b and GT1b displayed homogeneous distribution patterns in each membrane preparation. They were expressed only in small amounts but mainly in SL, TT and Tr/M vesicles and to less extent in SR1 and SR2 fractions. The presence of GM3(Neu5Ac) in the SL as well as on subcellular level was confirmed in transverse muscle cryosections by means of indirect immunofluorescence microscopy. The SL was brightly stained, but considerable intracellular fluorescence was observed as expected from the biochemical analyses. Thus, the neutral GSL and ganglioside expression of the SL and the intracellular membraneous network is different in skeletal muscle both in terms of quantitative and qualitative GSL composition as demonstrated in details by means of biochemical and immunochemical techniques. The modulatory functions of GM3 and gangliosides of the neolacto- and ganglio-series towards the voltage dependent Ca(2+)-channel, largely preponderant in the triads-containing Tr/M fraction, is the subject of the accompanying paper (J. Müthing, U. Maurer, and S. Weber-Schürholz, Carbohydr. Res., 307 (1998) 147-157).

Glycosphingolipid expression in human skeletal and heart muscle assessed by immunostaining thin-layer chromatography

In this study the comparative TLC immunostaining investigation of neutral GSLs and gangliosides from human skeletal and heart muscle is described. A panel of specific polyclonal and monoclonal antibodies as well as the GM1-specific choleragenoid were used for the overlay assays, combined with preceding neuraminidase treatment of gangliosides on TLC plates. This approach proved homologies but also quantitative and qualitative differences in the expression of ganglio-, globo- and neolacto-series neutral GSLs and gangliosides in these two types of striated muscle tissue within the same species. The main neutral GSL in skeletal muscle was LacCer, followed by GbOse3Cer, GbOse4Cer, nLcOse4Cer and monohexosylceramide, whereas in heart muscle GbOse3Cer and GbOse4Cer were the predominant neutral GSLs beside small quantities of LacCer, nLcOse4Cer and monohexosylceramide. No ganglio-series neutral GSLs and no Forssman GSL were found in either muscle tissue. GM3(Neu5Ac) was the major ganglioside, comprising almost 70% in skeletal and about 50% in cardiac muscle total gangliosides. GM2 was found in skeletal muscle only, while GD3 and GM1b-type gangliosides (GM1b and GD1 alpha) were undetectable in both tissues. GM1a-core gangliosides (GM1, GD1a, GD1b and GT1b) showed somewhat quantitative differences in each muscle; lactosamine-containing IV3Neu5Ac-nLcOse4Cer was detected in both specimens. Neutral GSLs were identified in TLC runs corresponding to e.g. 0.1 g muscle wet weight (GbOse3Cer, GbOse4Cer), and gangliosides GM3 and GM2 were elucidated in runs which corresponded to 0.2 g muscle tissue. Only 0.02 g and 0.004 g wet weight aliquots were necessary for unequivocal identification of neolacto-type and GM1-core gangliosides, respectively. Muscle is known for the lowest GSL concentration from all vertebrate tissues studied so far. Using the overlay technique, reliable GSL composition could be revealed, even from small muscle probes on a sub-orcinol and sub-resorcinol detection level.

Effects of ethanol on neuroblastoma cells in culture: role of gangliosides in neuritogenesis and substrate adhesion

Murine Neuro-2A neuroblastoma cells were exposed to ethanol in culture under two experimental paradigms: (1) short-term (24 hr or less) and low concentrations (0.05 to 0.5%; 8.5 to 86 mM) and (2) long-term (48 hr at 0.5%; 86 mM). Long-term ethanol exposure did not affect Neuro-2A viability, determined by DNA synthesis or the ability to exclude Trypan Blue. Similarly, long-term ethanol treatment did not inhibit differentiation, exhibited by the extension of neurites, promoted by either dibutyryl-cyclic-AMP or by incubation with exogenous ganglioside GM1. The incorporation of exogenous ganglioside GM1 into plasma membranes was not influenced by varying concentrations of ethanol (up to 1.2%; 204 mM). In contrast, ethanol did influence Neuro-2A cell attachment to collagen in a dualistic manner. During short-term ethanol exposure, cell attachment was enhanced. However, when cells were initially exposed to ethanol for 48 hr a marked inhibition of subsequent attachment was observed. Long-term ethanol exposure also inhibited attachment to other substrata, including laminin, fibronectin and vitronectin. Incubation of Neuro-2A cells with either exogenous ganglioside GM1 or a mixture of brain gangliosides partially reversed the inhibition of attachment to collagen. This reversal did not appear to be due to any one particular ganglioside structure, however. Mixed brain gangliosides were fractionated into three fractions, according to the number of sialic acid residues. Each of the three fractions were equally effective in partially restoring Neuro-2A cell attachment to collagen after long-term ethanol treatment. The results suggest that the mechanism by which these effects occur is at the level of plasma membrane fluidity, because both ethanol and glycosphingolipid content are known to influence membrane lateral mobility, although other mechanisms, such as changes in headgroup hydration, are possible.

Glycosphingolipids during skeletal muscle cell differentiation: comparison of normal and fusion-defective myoblasts

The regulation of glycosphingolipid (GSL) synthesis in culture by fusion-competent (E63) myoblasts and fusion-defective (fu-1) cells was examined. Upon reaching confluency E63 cells fused to form multinucleated myotubes and demonstrated many characteristics of developing skeletal muscle including induction of creatine kinase activity and a shift in creatine kinase isozymes to the MM isoform. The fu-1 cells displayed none of these characteristics, despite the fact that both cells were cloned from the same parental myoblast line (rat L8). There was a transient increase in the synthesis of total neutral GSLs by E63 cells at the time of membrane fusion. In contrast, neutral GSL synthesis by fu-1 cells gradually decreased with time in culture. The major GSLs synthesized by both cell types were lactosylceramide and ganglioside GM3, with more complex structures being observed with prolonged time in culture. Several glycosyltransferase activities were assayed at varying times in culture. Generally, the changes in activities fell into three groups. One group was maximally activated at the end of the culture period (GalT-3, GalNAcT-1 and GalT-6). Another group was maximally activated during the time of active membrane fusion (GlcT and SAT-1). A third group was maximally activated at the time of cell contact and the beginning of membrane fusion (GlcNAcT-1 and GalT-2). In terms of the times of maximal activation there were few differences between E63 and fu-1 cells, with one notable exception. The activity of GalT-2 (lactosylceramide synthase) in E63 cells increased dramatically upon contact and the beginning of membrane fusion, whereas there were no changes in GalT-2 activity in fu-1 cells during time in culture. These results support our hypothesis that membrane glycosphingolipids play an important role in the differentiation of skeletal muscle cells.

Regulation of glycolipid synthesis during differentiation of clonal murine muscle cells

The two clonal murine muscle cell lines G7 and G8, originally derived from the M114 line, represent unique models for comparative studies of myogenesis. Glycolipid synthesis was examined during differentiation using [3H]-galactose and [3H]-glucosamine as precursors. Upon G7 contact glucosylceramide labeling increased and nLcOse5Cer labeling stopped. During membrane fusion, glucosylceramide labeling stopped and lactosylceramide became the major synthetic product. G8 cells presented a different pattern, with increased labeling of GbOse3Cer during myogenesis. The major ganglioside synthesized by both myoblasts was GM3, and more complex structures were observed following completion of myotube formation. Total glycopeptide labeling increased when G8 myoblasts fused and remained elevated in myotubes, whereas no differences during fusion of G7 cells were noted. Upon comparison of the two clonal lines, the only consistent observation was a significant increase in the synthesis of total gangliosides and neutral glycolipid during cell contact and membrane fusion (p less than 0.02). The results suggest that changes in the synthesis of specific glycolipid structures during myogenesis are unique to each muscle cell line examined. However, transient increases in synthesis of total myoblast gangliosides and neutral glycolipids may be a more general phenomenon, possibly by curbing proliferation or by altering myoblast membrane fluidity characteristics during differentiation.