The role of protein glycosylation in muscle diseases

Simultaneous magnetic purification and detection of transferrin in human serum using an imprinting-based fluorescence sensor by boronate affinity and secondary signal amplification assay

Transferrin (TRF) is an important glycoprotein for the early detection of disease. However, its rapid isolation and detection are challenging due to its complex structure, composition, and susceptibility to denaturation. Herein, a novel imprinting-based sensor was introduced to purify and detect TRF in human serum simultaneously. A magnetic molecularly imprinted sensor was developed by integrating boronate affinity-based MIPs with a boric acid-functionalized rod-like fluorescent porphyrin (TCPP) aggregate (A-TCPP-BA) to form a sandwich structure. When an alkaline solution (pH 10) was added, the TCPP was re-released due to disruption in the structure of the A-TCPP-BA, leading to a second "explosive" amplification of fluorescence signals. Therefore, sensitive detection of TRF was realized with a good linear range from 2-50 μg mL-1 and a detection limit of 0.74 μg mL-1. Furthermore, five pre-diagnosed serum samples were analyzed using this approach, obtaining recoveries in the range of 97.4% to 104.4%. In addition, the results of the significance tests (p-values of all five samples are greater than 0.05) were satisfactory compared with those of electrochemiluminescence (ECL). Therefore, this method shows great potential for the point-of-care testing of TRF and other glycoproteins in the future.

Arginine N-glycosylation of melittin enhances its bacteriostatic activity and antiproliferative therapeutic index

Melittin is a natural antimicrobial peptide isolated from bee venom, and the non-specific cytotoxicity and hemolytic activity severely limit its clinical application. Glycosylation of proteins is very common in physiological and biochemical processes and can modulate the interaction of proteins with their target. In this study, eight glycosyl groups were used to modify the arginine of melittin at sites 22 and/or 24, and single and double arginine N-glycosylated peptides were designed and synthesized. Among the acquired 24 glycopeptides, MLT-1c, MLT-3c, MLT-1f, MLT-3f, MLT-1g, and MLT-3h were found to possess higher helicity, while MLT-3c, MLT-3f and MLT-3h showed dramatically reduced hemolytic activity, especially MLT-3c, whose HC50 value is 199.3 μM. MLT-1a, MLT-3a and MLT-2c exhibited improved inhibitory activity against Puzza streptococcus, and the MIC was 4 μg mL-1. MLT-1e and MLT-2g have the strongest tolerance to trypsase, and MLT-3c has the highest therapeutic index. In general, rhamnosyl-modified melittin MLT-3c could be a potent agent for antibacterial and antitumor therapy with high stability and low hemolytic side effects.

Drosophila melanogaster: A Model Organism in Muscular Dystrophy Studies

Muscular dystrophy is a group of complicated, genetically heterogeneous disorders characterized by progressive muscle weakness and degeneration. Due to the intricate nature, understanding the molecular mechanisms underlying muscular dystrophy presents significant challenges. Drosophila, as a versatile and genetically tractable model organism, offers substantial advantages in muscular dystrophy research. In the present review, we summarize the application of Drosophila in studying various types of muscular dystrophy, highlighting the insights gained through genetic manipulations, disease modeling, and the exploration of molecular pathways. Drosophila serves as a powerful system for understanding disease progression, exploring the roles of key genes in muscle function and pathology, and identifying novel therapeutic targets. The review highlights the significant role of Drosophila in advancing our understanding of muscular dystrophy.

Neurexin facilitates glycosylation of Dystroglycan to sustain muscle architecture and function in Drosophila

Neurexin, a molecule associated with autism spectrum disorders, is thought to function mainly in neurons. Recently, it was reported that Neurexin is also present in muscle, but the role of Neurexin in muscle is still poorly understood. Here, we demonstrate that the overexpression of Neurexin in muscles effectively restored the locomotor function of Drosophila neurexin mutants, while rescuing effects are observed within the nervous. Notably, the defects in muscle structure and function caused by Neurexin deficiency were similar to those caused by mutations in dystroglycan, a gene associated with progressive muscular dystrophy. The absence of Neurexin leads to muscle attachment defects, emphasizing the essential role of Neurexin in muscle integrity. Furthermore, Neurexin deficiency reduces Dystroglycan glycosylation on the cell surface, which is crucial for maintaining proper muscle structure and function. Finally, Neurexin guides Dystroglycan to the glycosyltransferase complex through interactions with Rotated Abdomen, a homolog of mammalian POMT1. Our findings reveal that Neurexin mediates muscle development and function through Dystroglycan glycosylation, suggesting a potential association between autism spectrum disorders and muscular dystrophy.

Interglycosidic C5-C6 rotamer distributions of alkyl O-rutinosides

The conformational study of carbohydrates is critical to understand the molecular recognition mechanisms underlying their biological functions. Moreover, the systematic study of their conformational patterns can unlock useful tools to design optimized glycomimetics and drug candidates. Using nuclear magnetic resonance, we studied the interglycosidic rotamer equilibria of ester-protected and deprotected alkyl O-rutinosides (α-L-Rha(1,6)β-D-GlcOR). In the protected series, the equilibrium about the C5-C6 bond distributes among the three possible rotamers gg, gt, and tg, being gt the predominant conformer. In these series, the flexibility about C5-C6 shows a marked dependency on the aglycone's structure, where the increase on the aglycone's volume leads to a progressive increment on the tg contributions at the expense of gt, with gg remaining practically constant along the series. The removal of the protective groups results in rutinosides displaying an equilibrium equally distributed between gg and gt with no tg contributions regardless of the aglycone's structure.

Protein Extraction Methods Suitable for Muscle Tissue Proteomic Analysis

Muscle tissue is one of the most dynamic and plastic tissues of the mammalian body and covers different roles, such as force generation and metabolic control. Muscular proteomics provides an important opportunity to reveal the molecular mechanisms behind muscle pathophysiology. To ensure successful proteomic analysis, it is necessary to have an efficient and reproducible protein extraction method. This study aimed to evaluate the efficacy of two different extraction protocols of muscle samples for two-dimensional gel electrophoresis. In particular, mouse muscle proteins were extracted by an SDS-based buffer (Method A) and by a UREA/CHAPS/DTE/TRIS solution (Method B). The efficacies of the methods were assessed by performing an image analysis of the 2DE gels and by statistical and multivariate analyses. The 2DE gels in both preparations showed good resolution and good spot overlapping. Methods A and B produced 2DE gels with different means of total spots, higher for B. Image analysis showed different patterns of protein abundance between the protocols. The results showed that the two methods extract and solubilize proteins with different chemical-physical characteristics and different cellular localizations. These results attest the efficacy and reproducibility of both protein extraction methods, which can be parallelly applied for comprehensive proteomic profiling of muscle tissue.

Gut microbiota disturbances in hospitalized older adults with malnutrition and clinical outcomes

OBJECTIVE

Malnutrition is one of the most threatening conditions in geriatric populations. The gut microbiota has an important role in the host's metabolic and muscular health: however, its interplay with disease-related malnutrition is not well understood. We aimed to identify the association of malnutrition with the gut microbiota and predict clinical outcomes in hospitalized acutely ill older adults.

METHODS

We performed a secondary longitudinal analysis in 108 geriatric patients from a prospective cohort evaluated at admission and 72 h of hospitalization. We collected clinical, demographic, nutritional, and 16S rRNA gene-sequenced gut microbiota data. Microbiota diversity, overall composition, and differential abundance were calculated and compared between patients with and without malnutrition. Microbiota features associated with malnutrition were used to predict clinical outcomes.

RESULTS

Patients with malnutrition (51%) had a different microbiota composition compared to those who were well-nourished during hospitalization (ANOSIM R = 0.079, P = 0.003). Patients with severe malnutrition showed poorer α-diversity at admission (Shannon P = 0.012, Simpson P = 0.018) and follow-up (Shannon P = 0.023, Chao1 P = 0.008). Differential abundance of Lachnospiraceae NK4A136 group, Subdoligranulum, and Faecalibacterium prausnitzii were significantly lower and inversely associated with malnutrition, while Corynebacterium, Ruminococcaceae Incertae Sedis, and Fusobacterium were significantly increased and positively associated with malnutrition. Corynebacterium, Ruminococcaceae Incertae Sedis, and the overall composition were important predictors of critical care in patients with malnutrition during hospitalization.

CONCLUSION

Older adults with malnutrition, especially in a severe stage, may be subject to substantial gut microbial disturbances during hospitalization. The gut microbiota profile of patients with malnutrition might help us to predict worse clinical outcomes.

Coronavirus accessory protein ORF3 biology and its contribution to viral behavior and pathogenesis

Coronavirus porcine epidemic diarrhea virus (PEDV) is classified in the genus Alphacoronavirus, family Coronaviridae that encodes the only accessory protein, ORF3 protein. However, how ORF3 contributes to viral pathogenicity, adaptability, and replication is obscure. In this review, we summarize current knowledge and identify gaps in many aspects of ORF3 protein in PEDV, with emphasis on its unique biological features, including membrane topology, Golgi retention mechanism, potential intrinsic disordered property, functional motifs, protein glycosylation, and codon usage phenotypes related to genetic evolution and gene expression. In addition, we propose intriguing questions related to ORF3 protein that we hope to stimulate further studies and encourage collaboration among virologists worldwide to provide constructive knowledge about the unique characteristics and biological functions of ORF3 protein, by which their potential role in clarifying viral behavior and pathogenesis can be possible.

Protein O-GlcNAcylation in Metabolic Modulation of Skeletal Muscle: A Bright but Long Way to Go

O-GlcNAcylation is an atypical, dynamic and reversible O-glycosylation that is critical and abundant in metazoan. O-GlcNAcylation coordinates and receives various signaling inputs such as nutrients and stresses, thus spatiotemporally regulating the activity, stability, localization and interaction of target proteins to participate in cellular physiological functions. Our review discusses in depth the involvement of O-GlcNAcylation in the precise regulation of skeletal muscle metabolism, such as glucose homeostasis, insulin sensitivity, tricarboxylic acid cycle and mitochondrial biogenesis. The complex interaction and precise modulation of O-GlcNAcylation in these nutritional pathways of skeletal muscle also provide emerging mechanical information on how nutrients affect health, exercise and disease. Meanwhile, we explored the potential role of O-GlcNAcylation in skeletal muscle pathology and focused on its benefits in maintaining proteostasis under atrophy. In general, these understandings of O-GlcNAcylation are conducive to providing new insights into skeletal muscle (patho) physiology.

CREBH alleviates mitochondrial oxidative stress through SIRT3 mediating deacetylation of MnSOD and suppression of Nlrp3 inflammasome in NASH

Lipotoxicity and unresolved oxidative stress are key drivers of metabolic inflammation in nonalcoholic steatohepatitis (NASH). cAMP-response element binding protein H(CREBH) is a liver-specific transcription factor and regulates the glucose and lipid metabolism of NASH. However, its role in mitochondrial oxidative stress and its association with sirtuin 3 (SIRT3), a master regulator of deacetylation for mitochondrial proteins, remains elusive. In this study, AML-12 cells were treated with palmitic acid to imitate the pathological changes of NASH in vitro and 8-week-old male C57BL/6J mice were fed with a high-fat (HF) diet or a methionine-choline-deficient (MCD) diet to build the widely accepted in vivo model of NASH. We found that lipid overload induced mitochondrial oxidative stress and stimulated the expression of CREBH and SIRT3. CREBH overexpression alleviated the mitochondrial oxidative stress. Moreover, CREBH promoted SIRT3 expression, which regulated the deacetylation of manganese superoxide dismutase (MnSOD) and inhibited NOD-Like Receptor Pyrin Domain Containing 3 (Nlrp3) inflammasome activation whereas suppression of SIRT3 damaged the protecting ability of CREBH in mitochondrial oxidative stress. CREBH knockout mice were highly susceptible to HF and MCD diet-induced NASH with more severe oxidative stress. Collectively, our results firstly provided the support that CREBH could serve as a protective factor in the progression of NASH by regulating the acetylation of MnSOD and the activation of Nlrp3 inflammasome through SIRT3. These results suggest that CREBH might be a valuable therapeutic candidate for NASH.