Clinical features of Danon disease and insights gained from LAMP-2 deficiency models

Methylmalonic acidemia triggers lysosomal-autophagy dysfunctions

BACKGROUND

Methylmalonic acidemia (MMA) is a rare inborn error of propionate metabolism caused by deficiency of the mitochondrial methylmalonyl-CoA mutase (MUT) enzyme. As matter of fact, MMA patients manifest impairment of the primary metabolic network with profound damages that involve several cell components, many of which have not been discovered yet. We employed cellular models and patients-derived fibroblasts to refine and uncover new pathologic mechanisms connected with MUT deficiency through the combination of multi-proteomics and bioinformatics approaches.

RESULTS

Our data show that MUT deficiency is connected with profound proteome dysregulations, revealing molecular actors involved in lysosome and autophagy functioning. To elucidate the effects of defective MUT on lysosomal and autophagy regulation, we analyzed the morphology and functionality of MMA-lysosomes that showed deep alterations, thus corroborating omics data. Lysosomes of MMA cells present as enlarged vacuoles with low degradative capabilities. Notwithstanding, treatment with an anti-propionigenic drug is capable of totally rescuing lysosomal morphology and functional activity in MUT-deficient cells. These results indicate a strict connection between MUT deficiency and lysosomal-autophagy dysfunction, providing promising therapeutic perspectives for MMA.

CONCLUSIONS

Defective homeostatic mechanisms in the regulation of autophagy and lysosome functions have been demonstrated in MUT-deficient cells. Our data prove that MMA triggers such dysfunctions impacting on autophagosome-lysosome fusion and lysosomal activity.

Characterization of three lamp genes from largemouth bass (Micropterus salmoides): molecular cloning, expression patterns, and their transcriptional levels in response to fast and refeeding strategy

Lysosomes-associated membrane proteins (LAMPs), a family of glycosylated proteins and major constituents of the lysosomal membranes, play a dominant role in various cellular processes, including phagocytosis, autophagy and immunity in mammals. However, their roles in aquatic species remain poorly known. In the present study, three lamp genes were cloned and characterized from Micropterus salmoides. Subsequently, their transcriptional levels in response to different nutritional status were investigated. The full-length coding sequences of lamp1, lamp2 and lamp3 were 1251bp, 1224bp and 771bp, encoding 416, 407 and 256 amino acids, respectively. Multiple sequence alignment showed that LAMP1-3 were highly conserved among the different fish species, respectively. 3-D structure prediction, genomic survey, and phylogenetic analysis were further confirmed that these genes are widely existed in vertebrates. The mRNA expression of the three genes was ubiquitously expressed in all selected tissues, including liver, brain, gill, heart, muscle, spleen, kidney, stomach, adipose and intestine, lamp1 shows highly transcript levels in brain and muscle, lamp2 displays highly expression level in heart, muscle and spleen, but lamp3 shows highly transcript level in spleen, liver and kidney. To analyze the function of the three genes under starvation stress in largemouth bass, three experimental treatment groups (fasted group and refeeding group, control group) were established in the current study. The results indicated that the expression of lamp1 was significant induced after starvation, and then returned to normal levels after refeeding in the liver. The expression of lamp2 and lamp3 exhibited the same trend in the liver. In addition, in the spleen and the kidney, the transcript level of lamp1 and lamp2 was remarkably increased in the fasted treatment group and slightly decreased in the refed treatment group, respectively. Collectively, our findings suggest that three lamp genes may have differential function in the immune and energetic organism in largemouth bass, which is helpful in understanding roles of lamps in aquatic species.

State of Gene Therapy for Monogenic Cardiovascular Diseases

Over the past 2 decades, significant efforts have been made to advance gene therapy into clinical practice. Although successful examples exist in other fields, gene therapy for the treatment of monogenic cardiovascular diseases lags behind. In this review, we (1) highlight a brief history of gene therapy, (2) distinguish between gene silencing, gene replacement, and gene editing technologies, (3) discuss vector modalities used in the field with a special focus on adeno-associated viruses, (4) provide examples of gene therapy approaches in cardiomyopathies, channelopathies, and familial hypercholesterolemia, and (5) present current challenges and limitations in the gene therapy field.

Case Report: Multiple types of arrhythmias in a late-confirmed Danon disease

Introduction

Danon disease is an X-linked disorder caused by pathogenic variants in lysosome-associated membrane protein 2 (LAMP2) gene, typically characterized by the triad of hypertrophic cardiomyopathy, myopathy, and intellectual disability. However, many patients may not present the typical presentation, especially in the early stage. Electrocardiogram (ECG) abnormalities can be found in almost all patients, with Wolff-Parkinson-White (WPW) syndrome being the most common. We reported the case of a 51-year-old woman who experienced multiple types of arrhythmias over three decades and was diagnosed with Danon disease late by genetic testing.

Case summary

A 51-year-old woman with a 36-year history of intermittent palpitations was admitted due to hemodynamically stable ventricular tachycardia (VT). Her past medical history revealed multiple arrhythmias and ECG abnormalities in her 30s and 40s, including WPW syndrome with paroxysmal supraventricular tachycardia, paroxysmal atrial flutter, atrial fibrillation, ventricular tachycardia, and complete left bundle branch block. She denied any family history of cardiovascular disease or sudden death. Upon arrival, her vital signs were unremarkable. Cardiovascular magnetic resonance (CMR) imaging revealed left ventricular enlargement and late gadolinium enhancement (LGE) in the anterior, inferior, and lateral walls. Subsequent, whole-exome sequencing (WES) gene testing revealed a pathogenic heterozygous variant in LAMP2 gene (c.696T>A; p.Cys232Ter), which confirmed the diagnosis of Danon disease.

Conclusion

Genetic testing should be considered in patients who display multiple arrhythmias with LV structural abnormalities of unknown etiology for a possible Danon disease.

Rab44 deficiency accelerates recovery from muscle damage by regulating mTORC1 signaling and transport of fusogenic regulators

The skeletal muscle is a tissue that shows remarkable plasticity to adapt to various stimuli. The development and regeneration of skeletal muscles are regulated by numerous molecules. Among these, we focused on Rab44, a large Rab GTPase, that has been recently identified in immune cells and osteoclasts. Recently, bioinformatics data has revealed that Rab44 is upregulated during the myogenic differentiation of myoblasts into myotubes in C2C12 cells. Thus, Rab44 may be involved in myogenesis. Here, we have investigated the effects of Rab44 deficiency on the development and regeneration of skeletal muscle in Rab44 knockout (KO) mice. Although KO mice exhibited body and muscle weights similar to those of wild-type (WT) mice, the histochemical analysis showed that the myofiber cross-sectional area (CSA) of KO mice was significantly smaller than that of WT mice. Importantly, the results of muscle regeneration experiments using cardiotoxin revealed that the CSA of KO mice was significantly larger than that of WT mice, suggesting that Rab44 deficiency promotes muscle regeneration. Consistent with the in vivo results, in vitro experiments indicated that satellite cells derived from KO mice displayed enhanced proliferation and differentiation. Mechanistically, KO satellite cells exhibited an increased mechanistic target of rapamycin complex 1 (mTORC1) signaling compared to WT cells. Additionally, enhanced cell surface transport of myomaker and myomixer, which are essential membrane proteins for myoblast fusion, was observed in KO satellite cells compared to WT cells. Therefore, Rab44 deficiency enhances muscle regeneration by modulating the mTORC1 signaling pathway and transport of fusogenic regulators.

Identification of a novel splicing-altering LAMP2 variant in a Chinese family with Danon disease

AIMS

This study aimed to identify a novel splicing-altering LAMP2 variant associated with Danon disease.

METHODS AND RESULTS

To identify the potential genetic mutation in a Chinese pedigree, whole-exome sequencing was conducted in the proband, and Sanger sequencing was performed on the proband's parents. To verify the impact of the splice-site variant, a minigene splicing assay was applied. The AlphaFold2 analysis was used to analyse the mutant protein structure. A splice-site variant (NM_013995.2:c.864+5G>A) located at intron 6 of the LAMP2 gene was identified as a potential pathogenic variant. The minigene splicing revealed that this variant causes exon 6 to be skipped, resulting in a truncated protein. The AlphaFold2 analysis showed that the mutation caused a protein twist direction change, leading to conformational abnormality.

CONCLUSIONS

A novel splice-site variant (NM_013995.2:c.864+5G>A) located at intron 6 of the LAMP2 gene was identified. This discovery may enlarge the LAMP2 variant spectrum, promote accurate genetic counselling, and contribute to the diagnosis of Danon disease.

Deciphering core proteins of osteoporosis with iron accumulation by proteomics in human bone

Iron accumulation is an independent risk factor for postmenopausal osteoporosis, but mechanistic studies of this phenomenon are still focusing on molecular and genetic researches in model animal. Osteoporosis with iron accumulation is a distinct endocrine disease with complicated pathogenesis regulated by several proteins. However, the comprehensive proteome-wide analysis of human bone is lacking. Using multiplex quantitative tandem mass tag-based proteomics, we detected 2900 and quantified 1150 proteins from bone of 10 postmenopausal patients undergoing hip replacement. Comparing with non-osteoporosis patients, a total of 75 differentially expressed proteins were identified, comprising 53 downregulated proteins and 22 upregulated proteins. These proteins primarily affect oxidoreductase activity, GTPase activity, GTP binding, and neural nucleus development, were mainly enriched in neural, angiogenesis and energy-related pathways, and formed complex regulatory networks with strong interconnections. We ultimately identified 4 core proteins (GSTP1, LAMP2, COPB1, RAB5B) that were significantly differentially expressed in the bone of osteoporosis patients with iron accumulation, and validated the changed protein level in the serum of the medical examination population. Our systemic analysis uncovers molecular insights for revealing underlying mechanism and clinical therapeutics in osteoporosis with iron accumulation.