Lysosomal Abnormalities in Cardiovascular Disease

A lysosome-located and rhodamine-based fluorescence probe for recognizing hydrogen polysulfide

Hydrogen polysulfide (H2Sn, n≥2), as a kind of active sulfur species (RSS), has become a hot topic in RSS. It can regulate the biological activity of many proteins through S-sulfhydrylation of cysteine residues (protein Cys-SSH), and has a protective effect on cells. Although there have been some studies on hydrogen polysulfide, its production, degradation pathway and regulation mechanism still need further be researched. In presented study, an original lysosome-localized fluorescent probe for determining H2Sn was developed utilizing rhodamine as the fluorogen. The probe used morpholine as the locating unit of lysosomes and chose 2-fluoro-5-nitrobenzoate as the recognizing group. Before adding H2Sn, the proposed probe displayed a spironolactone structure and emitted very weak fluorescence. After adding H2Sn, a conjugated xanthene was formed and the probe demonstrated green fluorescence. When the H2Sn concentration was varied from 6.0×10-7 mol·L-1 to 10.0×10-5 mol·L-1, the fluorescence intensity of the probe was linearly dependent on the H2Sn concentration. And the detection limit was 1.5×10-7 mol·L-1. The presented probe owned a fast response speed, good selectivity, excellent sensitivity and broad pH work scope. In addition, the probe had been well utilized to sense endogenic and exogenic H2Sn in lysosomes.

Mimicomes: Mimicking Multienzyme System by Artificial Design

Enzymes are widely distributed in organelles of cells, which are capable of carrying out specific catalytic reactions. In general, several enzymes collaborate to facilitate complex reactions and engage in vital biochemical processes within cells, which are also called cascade systems. The cascade systems are highly efficient, and their dysfunction is associated with a multitude of endogenous diseases. The advent of nanotechnology makes it possible to mimic these cascade systems in nature and realize partial functions of natural biological processes both in vitro and in vivo. To emphasize the significance of artificial cascade systems, mimicomes is first proposed, a new concept that refers to the artificial cascade catalytic systems. Typically, mimicomes are able to mimic specific natural biochemical catalytic processes or facilitate the overall catalytic efficiency of cascade systems. Subsequently, the evolution and development of different types of mimicomes in recent decades are elucidated exhaustedly, from the natural enzyme-based mimicomes (immobilized enzyme and vesicle mimicomes) to the nanozyme-based mimicomes and enzyme-nanozyme hybrid mimicomes. In conclusion, the remaining challenges in the design of multifunctional mimicomes and their potential applications are summarized, offering insights into their future prospects.

Programmed death of cardiomyocytes in cardiovascular disease and new therapeutic approaches

Cardiovascular diseases (CVDs) have a complex pathogenesis and pose a major threat to human health. Cardiomyocytes have a low regenerative capacity, and their death is a key factor in the morbidity and mortality of many CVDs. Cardiomyocyte death can be regulated by specific signaling pathways known as programmed cell death (PCD), including apoptosis, necroptosis, autophagy, pyroptosis, and ferroptosis, etc. Abnormalities in PCD can lead to the development of a variety of cardiovascular diseases, and there are also molecular-level interconnections between different PCD pathways under the same cardiovascular disease model. Currently, the link between programmed cell death in cardiomyocytes and cardiovascular disease is not fully understood. This review describes the molecular mechanisms of programmed death and the impact of cardiomyocyte death on cardiovascular disease development. Emphasis is placed on a summary of drugs and potential therapeutic approaches that can be used to treat cardiovascular disease by targeting and blocking programmed cell death in cardiomyocytes.

A genetically-encoded fluorescence-based reporter to spatiotemporally investigate mannose-6-phosphate pathway

Maintenance of a pool of active lysosomes with acidic pH and degradative hydrolases is crucial for cell health. Abnormalities in lysosomal function are closely linked to diseases, such as lysosomal storage disorders, neurodegeneration, intracellular infections, and cancer among others. Emerging body of research suggests the malfunction of lysosomal hydrolase trafficking pathway to be a common denominator of several disease pathologies. However, available conventional tools to assess lysosomal hydrolase trafficking are insufficient and fail to provide a comprehensive picture about the trafficking flux and location of lysosomal hydrolases. To address some of the shortcomings, we designed a genetically-encoded fluorescent reporter containing a lysosomal hydrolase tandemly tagged with pH sensitive and insensitive fluorescent proteins, which can spatiotemporally trace the trafficking of lysosomal hydrolases. As a proof of principle, we demonstrate that the reporter can detect perturbations in hydrolase trafficking, that are induced by pharmacological manipulations and pathophysiological conditions like intracellular protein aggregates. This reporter can effectively serve as a probe for mapping the mechanistic intricacies of hydrolase trafficking pathway in health and disease and is a utilitarian tool to identify genetic and pharmacological modulators of this pathway, with potential therapeutic implications.

Compartmentalization proteomics revealed endolysosomal protein network changes in a goat model of atrial fibrillation

Endolysosomes (EL) are known for their role in regulating both intracellular trafficking and proteostasis. EL facilitate the elimination of damaged membranes, protein aggregates, membranous organelles and play an important role in calcium signaling. The specific role of EL in cardiac atrial fibrillation (AF) is not well understood. We isolated atrial EL organelles from AF goat biopsies and conducted a comprehensive integrated omics analysis to study the EL-specific proteins and pathways. We also performed electron tomography, protein and enzyme assays on these biopsies. Our results revealed the upregulation of the AMPK pathway and the expression of EL-specific proteins that were not found in whole tissue lysates, including GAA, DYNLRB1, CLTB, SIRT3, CCT2, and muscle-specific HSPB2. We also observed structural anomalies, such as autophagic-vacuole formation, irregularly shaped mitochondria, and glycogen deposition. Our results provide molecular information suggesting EL play a role in AF disease process over extended time frames.

eIF2α-mediated integrated stress response links multiple intracellular signaling pathways to reprogram vascular smooth muscle cell fate in carotid artery plaque

Background

Carotid arterial atherosclerotic stenosis is a well-recognized pathological basis of ischemic stroke; however, its underlying molecular mechanisms remain unknown. Vascular smooth muscle cells (VSMCs) play fundamental roles in the initiation and progression of atherosclerosis. Organelle dynamics have been reported to affect atherosclerosis development. However, the association between organelle dynamics and various cellular stresses in atherosclerotic progression remain ambiguous.

Methods

In this study, we conducted transcriptomics and bioinformatics analyses of stable and vulnerable carotid plaques. Primary VSMCs were isolated from carotid plaques and subjected to histopathological staining to determine their expression profiles. Endoplasmic reticulum (ER), mitochondria, and lysosome dynamics were observed in primary VSMCs and VSMC cell lines using live-cell imaging. Moreover, the mechanisms underlying disordered organelle dynamics were investigated using comprehensive biological approaches.

Results

ER whorls, a representative structural change under ER stress, are prominent dynamic reconstructions of VSMCs between vulnerable and stable plaques, followed by fragmented mitochondria and enlarged lysosomes, suggesting mitochondrial stress and lysosomal defects, respectively. Induction of mitochondrial stress alleviated ER stress and autophagy in an eukaryotic translation initiation factor (eIF)-2α-dependent manner. Furthermore, the effects of eIF2α on ER stress, mitochondrial stress, and lysosomal defects were validated using clinical samples.

Conclusion

Our results indicate that morphological and functional changes in VSMC organelles, especially in ER whorls, can be used as reliable biomarkers for atherosclerotic progression. Moreover, eIF2α plays an important role in integrating multiple stress-signaling pathways to determine the behavior and fate of VSMCs.

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.

Pathophysiology of Lysosomes in a Nutshell

Lysosomes are acidic organelles present in all nucleated mammalian cells [...].

Lysosomal dysfunction induced cytosolic vacuolation and increased intracellular amyloid-beta 42 (Aβ42) in human brain endothelial cells (HBEC-5i)

Lysosome is a primary degradative organelle and is crucial in cellular homeostasis. A reduction in its function due to ageing has been associated with the development of Alzheimer's disease (AD), a common neurodegenerative disorder characterised by the deposition of neurotoxic amyloid plaque in the brain and cerebral vessel walls. The breakdown of the blood-brain barrier (BBB) plays a vital role in the pathogenesis of AD. However, the impact of lysosomal dysfunction on brain endothelial cells, the key component of the BBB, in the disease progression is yet to be fully understood. In this study, human brain endothelial cells (HBEC-5i) were exposed to a lysosomotropic compound, chloroquine (CQ) for 24 h. Cell viability was assessed with the 3-(4,5-dimethylthiazol-2-yl)- 2,5-diphenyltetrazolium bromide (MTT) assay to determine the inhibitory concentration (IC) at IC₁₀ (17.5 µM), IC₂₅ (70.5 µM), and IC₅₀ (125 µM). The morphological changes observed include vacuoles arrested in the cytosols and cell shrinkage that were more prominent at IC₂₅ and IC₅₀. Lysosomal dysfunction was evaluated by measuring the lysosomal-associated membrane protein-1 (LAMP-1) and microtubule-associated protein light chain 3-II (LC3-II) using the capillary-based immunoassay. LC3-II was significantly increased at IC₂₅ and IC₅₀ (p < 0.05 and p < 0.001_, respectively). The concentration of intracellular and extracellular Aβ42 was quantitated using the enzyme-linked immunosorbent assay, which demonstrated a significant increase (p < 0.05) in intracellular Aβ42 at IC₂₅. This study showed that perturbation of lysosomal function impairs autophagy that leads to intracellular increment of Aβ, indicating the important roles of lysosomes in endothelial cells homeostasis and disease progression.

The regulatory mechanism between lysosomes and mitochondria in the aetiology of cardiovascular diseases

Coordinated action among various organelles maintains cellular functions. For instance, mitochondria and lysosomes are the main organelles contributing to cellular metabolism and provide energy for cardiomyocyte contraction. They also provide essential signalling platforms in the cell that regulate many key processes such as autophagy, apoptosis, oxidative stress, inflammation and cell death. Often, abnormalities in mitochondrial or lysosomal structures and functions bring about cardiovascular diseases (CVDs). Although the communication between mitochondria and lysosomes throughout the cardiovascular system is intensely studied, the regulatory mechanisms have not been completely understood. Thus, we summarize the most recent studies related to mitochondria and lysosomes' role in CVDs and their potential connections and communications under cardiac pathophysiological conditions. Further, we discuss limitations and future perspectives regarding diagnosis, therapeutic strategies and drug discovery in CVDs.

New Molecular and Organelle Alterations Linked to Down Syndrome Heart Disease

Down syndrome (DS) is a genetic disorder caused by a trisomy of the human chromosome 21 (Hsa21). Overexpression of Hsa21 genes that encode proteins and non-coding RNAs (ncRNAs) can disrupt several cellular functions and biological processes, especially in the heart. Congenital heart defects (CHDs) are present in 45–50% of individuals with DS. Here, we describe the genetic background of this condition (Hsa21 and non-Hsa21 genes), including the role of ncRNAs, and the relevance of these new players in the study of the pathophysiology of DS heart diseases. Additionally, we discuss several distinct pathways in cardiomyocytes which help maintain a functional heart, but that might trigger hypertrophy and oxidative stress when altered. Moreover, we highlight the importance of investigating how mitochondrial and lysosomal dysfunction could eventually contribute to understanding impaired heart function and development in subjects with the Hsa21 trisomy. Altogether, this review focuses on the newest insights about the gene expression, molecular pathways, and organelle alterations involved in the cardiac phenotype of DS.

A Compendium of Information on the Lysosome

For a long time, lysosomes were considered as mere waste bags for cellular constituents. Thankfully, studies carried out in the past 15 years were brimming with elegant and crucial breakthroughs in lysosome research, uncovering their complex roles as nutrient sensors and characterizing them as crucial multifaceted signaling organelles. This review presents the scientific knowledge on lysosome physiology and functions, starting with their discovery and reviewing up to date ground-breaking discoveries highlighting their heterogeneous functions as well as pending questions that remain to be answered. We also review the roles of lysosomes in anti-cancer drug resistance and how they undergo a series of molecular and functional changes during malignant transformation which lead to tumor aggression, angiogenesis, and metastases. Finally, we discuss the strategy of targeting lysosomes in cancer which could lead to the development of new and effective targeted therapies.

Lysosome (Dys)function in Atherosclerosis-A Big Weight on the Shoulders of a Small Organelle

Atherosclerosis is a progressive insidious chronic disease that underlies most of the cardiovascular pathologies, including myocardial infarction and ischemic stroke. The malfunctioning of the lysosomal compartment has a central role in the etiology and pathogenesis of atherosclerosis. Lysosomes are the degradative organelles of mammalian cells and process endogenous and exogenous substrates in a very efficient manner. Dysfunction of these organelles and consequent inefficient degradation of modified low-density lipoproteins (LDL) and apoptotic cells in atherosclerotic lesions have, therefore, numerous deleterious consequences for cellular homeostasis and disease progression. Lysosome dysfunction has been mostly studied in the context of the inherited lysosomal storage disorders (LSDs). However, over the last years it has become increasingly evident that the consequences of this phenomenon are more far-reaching, also influencing the progression of multiple acquired human pathologies, such as neurodegenerative diseases, cancer, and cardiovascular diseases (CVDs). During the formation of atherosclerotic plaques, the lysosomal compartment of the various cells constituting the arterial wall is under severe stress, due to the tremendous amounts of lipoproteins being processed by these cells. The uncontrolled uptake of modified lipoproteins by arterial phagocytic cells, namely macrophages and vascular smooth muscle cells (VSMCs), is the initial step that triggers the pathogenic cascade culminating in the formation of atheroma. These cells become pathogenic "foam cells," which are characterized by dysfunctional lipid-laden lysosomes. Here, we summarize the current knowledge regarding the origin and impact of the malfunctioning of the lysosomal compartment in plaque cells. We further analyze how the field of LSD research may contribute with some insights to the study of CVDs, particularly how therapeutic approaches that target the lysosomes in LSDs could be applied to hamper atherosclerosis progression and associated mortality.

Mitochondrial Homeostasis Mediates Lipotoxicity in the Failing Myocardium

Heart failure remains the most common cause of death in the industrialized world. In spite of new therapeutic interventions that are constantly being developed, it is still not possible to completely protect against heart failure development and progression. This shows how much more research is necessary to understand the underlying mechanisms of this process. In this review, we give a detailed overview of the contribution of impaired mitochondrial dynamics and energy homeostasis during heart failure progression. In particular, we focus on the regulation of fatty acid metabolism and the effects of fatty acid accumulation on mitochondrial structural and functional homeostasis.

Targeted Quantification of the Lysosomal Proteome in Complex Samples

In eukaryotic cells, lysosomes play a crucial role in the breakdown of a variety of components ranging from small molecules to complex structures, ascertaining the continuous turnover of cellular building blocks. Furthermore, they act as a regulatory hub for metabolism, being crucially involved in the regulation of major signaling pathways. Currently, ~450 lysosomal proteins can be reproducibly identified in a single cell line by mass spectrometry, most of which are low-abundant, restricting their unbiased proteomic analysis to lysosome-enriched fractions. In the current study, we applied two strategies for the targeted investigation of the lysosomal proteome in complex samples: data-independent acquisition (DIA) and parallel reaction monitoring (PRM). Using a lysosome-enriched fraction, mouse embryonic fibroblast whole cell lysate, and mouse liver whole tissue lysate, we investigated the capabilities of DIA and PRM to investigate the lysosomal proteome. While both approaches identified and quantified lysosomal proteins in all sample types, and their data largely correlated, DIA identified on average more proteins, especially for lower complex samples and longer chromatographic gradients. For the highly complex tissue sample and shorter gradients, however, PRM delivered a better performance regarding both identification and quantification of lysosomal proteins. All data are available via ProteomeXchange with identifier PXDD023278.