Modeling Sialidosis with Neural Precursor Cells Derived from Patient-Derived Induced Pluripotent Stem Cells

Cellular translocation and secretion of sialidases

Sialidases (or neuraminidases) catalyze the hydrolysis of sialic acid (Sia)-containing molecules, mostly the removal of the terminal Sia on glycans (desialylation) of either glycoproteins or glycolipids. Therefore, sialidases can modulate the functionality of the target glycoprotein or glycolipid and are involved in various biological pathways in health and disease. In mammalian cells, there are four kinds of sialidase, which are Neu1, Neu2, Neu3, and Neu4, based on their subcellular locations and substrate specificities. Neu1 is the lysosomal sialidase, Neu2 is the cytosolic sialidase, Neu3 is the plasma membrane-associated sialidase, and Neu4 is found in the lysosome, mitochondria, and endoplasmic reticulum. In addition to specific subcellular locations, sialidases can translocate to different subcellular localizations within particular cell conditions and stimuli, thereby participating in different cellular functions depending on their loci. Lysosomal sialidase Neu1 can translocate to the cell surface upon cell activation in several cell types, including immune cells, platelets, endothelial cells, and epithelial cells, where it desialylates receptors and thus impacts receptor activation and signaling. On the other hand, cells secrete sialidases upon activation. Secreted sialidases can serve as extracellular sialidases and cause the desialylation of both extracellular glycoproteins or glycolipids and cell surface glycoproteins or glycolipids on their own and other cells, thus playing roles in various biological pathways as well. This review discusses the recent advances and understanding of sialidase translocation in different cells and secretion from different cells under different conditions and their involvement in physiological and pathological pathways.

Low molecular weight fucoidan restores diabetic endothelial glycocalyx by targeting neuraminidase2: A new therapy target in glycocalyx shedding

BACKGROUND AND PURPOSE

Diabetic vascular complication is a leading cause of disability and mortality in diabetes patients. Low molecular weight fucoidan (LMWF) is a promising drug candidate for vascular complications. Glycocalyx injury predates the occurrence of diabetes vascular complications. Protecting glycocalyx from degradation relieves diabetic vascular complications. LMWF has the potential to protect the diabetes endothelial glycocalyx from shedding.

EXPERIMENTAL APPROACH

The protective effect of LMWF on diabetic glycocalyx damage was investigated in db/db mice and Human Umbilical Vein Endothelial Cells (HUVEC) through transmission electron microscopy and WGA labelling. The effect of LMWF on glycocalyx degrading enzymes expression was investigated. Neuraminidase2 (NEU2) overexpression/knockdown was performed in HUVECs to verify the important role of NEU2 in glycocalyx homeostasis. The interaction between NEU2 and LMWF was detected by ELISA and surface plasmon resonance analysis (SPR).

KEY RESULTS

LMWF normalizes blood indexes including insulin, triglyceride, uric acid and reduces diabetes complications adverse events. LMWF alleviates diabetic endothelial glycocalyx damage in db/db mice kidney/aorta and high concentration glucose treated HUVECs. NEU2 is up-regulated in db/db mice and HUVECs with high concentration glucose. Overexpression/knockdown NEU2 results in glycocalyx shedding in HUVEC. Down-regulation and interaction of LMWF with NEU2 is a new therapy target in glycocalyx homeostasis. NEU2 was positively correlated with phosphorylated IR-β.

CONCLUSION AND IMPLICATIONS

NEU2 is an effective target for glycocalyx homeostasis and LMWF is a promising drug to alleviate vascular complications in diabetes by protecting endothelial glycocalyx.

Sialic acid biosynthesis pathway blockade disturbs neuronal network formation in human iPSC-derived excitatory neurons

N-acetylneuraminic acid (sialic acid) is present in large quantities in the brain and plays a crucial role in brain development, learning, and memory formation. How sialic acid contributes to brain development is not fully understood. The purpose of this study was to determine the effects of reduced sialylation on network formation in human iPSC-derived neurons (iNeurons). Using targeted mass spectrometry and antibody binding, we observed an increase in free sialic acid and polysialic acid during neuronal development, which was disrupted by treatment of iNeurons with a synthetic inhibitor of sialic acid biosynthesis. Sialic acid inhibition disturbed synapse formation and network formation on microelectrode array (MEA), showing short but frequent (network) bursts and an overall lower firing rate, and higher percentage of random spikes. This study shows that sialic acid is necessary for neuronal network formation during human neuronal development and provides a physiologically relevant model to study the role of sialic acid in patient-derived iNeurons.

Delineating the neuropathology of lysosomal storage diseases using patient-derived induced pluripotent stem cells

Lysosomal storage diseases (LSD) are inherited metabolic diseases caused due to deficiency of lysosomal enzymes, essential for the normal development of the brain and other organs. Approximately two-thirds of the patients suffering from LSD exhibit neurological deficits and impose an escalating challenge to the medical and scientific field. The advent of iPSC technology has aided researchers in efficiently generating functional neuronal and non-neuronal cells through directed differentiation protocols, as well as in decoding the cellular, subcellular and molecular defects associated with LSDs using two-dimensional cultures and cerebral organoid models. This review highlights the information assembled from patient-derived iPSCs on neurodevelopmental and neuropathological defects identified in LSDs. Multiple studies have identified neural progenitor cell migration and differentiation defects, substrate accumulation, axon growth and myelination defects, impaired calcium homeostasis and altered electrophysiological properties, using patient-derived iPSCs. In addition, these studies have also uncovered defective lysosomes, mitochondria, endoplasmic reticulum, Golgi complex, autophagy and vesicle trafficking and signaling pathways, oxidative stress, neuroinflammation, blood brain barrier dysfunction, neurodegeneration, gliosis, altered transcriptomes in LSDs. The review also discusses the therapeutic applications such as drug discovery, repurposing of drugs, synergistic effects of drugs, targeted molecular therapies, gene therapy, and transplantation applications of mutation corrected lines identified using patient-derived iPSCs for different LSDs.

Inborn errors of metabolism: Lessons from iPSC models

The possibility of reprogramming human somatic cells to pluripotency has opened unprecedented opportunities for creating genuinely human experimental models of disease. Inborn errors of metabolism (IEMs) constitute a greatly heterogeneous class of diseases that appear, in principle, especially suited to be modeled by iPSC-based technology. Indeed, dozens of IEMs have already been modeled to some extent using patient-specific iPSCs. Here, we review the advantages and disadvantages of iPSC-based disease modeling in the context of IEMs, as well as particular challenges associated to this approach, together with solutions researchers have proposed to tackle them. We have structured this review around six lessons that we have learnt from those previous modeling efforts, and that we believe should be carefully considered by researchers wishing to embark in future iPSC-based models of IEMs.

Altered Gene Expression Profiles in Neural Stem Cells Derived from Duchenne Muscular Dystrophy Patients with Intellectual Disability

Intellectual disability (ID) is a neurodevelopmental disorder defined by below-average intelligence (intelligence quotient of <70) accompanied by adaptive behavior deficits. Defects in the functions of neural stem cells during brain development are closely linked to the pathogenesis of ID. To understand the molecular etiology of ID, we examined neural stem cells from individuals with Duchenne muscular dystrophy (DMD), a genetic disorder in which approximately one-third of the patients exhibit ID. In this study, we generated induced pluripotent stem cells from peripheral blood mononuclear cells from a normal individual and DMD patients with and without ID to identify ID-specific functional and molecular abnormalities. We found defects in neural ectoderm formation in the group of DMD patients with ID. Our transcriptome analysis of patient-derived neural stem cells revealed altered expression of genes related to the hippo signaling pathway and neuroactive ligand-receptor interaction, implicating these in the pathogenesis of ID in patients with DMD.