Biology subjects

Kwok, T.

Publications and source records attributed to Kwok, T..

6 recordsLinked to original sources

bioRxiv2026

Spatial control of mitochondrial retrograde signaling by nuclear pore-associated contact sites

Mitochondria relay their functional state to the nucleus via retrograde signaling, yet whether the spatial organization of the mitochondrial network plays a role in this process remains unclear. Here, we show that stress-induced clustering of mitochondria around the nucleus is a crucial part of the retrograde response. Perinuclear clustering facilitates the formation of mitochondria- nucleus contact sites (MNCS) and the nuclear entry of GPS2, a key mediator of mitochondrial retrograde signaling essential for activating nuclear-encoded mitochondrial and stress-response genes in response to various mitochondrial stressors. Unexpectedly, TSPO-driven MNCS are dispensable for GPS2-based retrograde signaling. Instead, we identify the mitochondrial import receptor TOMM70 and the nucleoporin RanBP2/NUP358 as components of a stress-induced nuclear pore-associated tethering complex required for promoting GPS2 nuclear translocation and activation of downstream programs. These findings establish MNCS as a functional gateway for mitochondrial retrograde signaling, highlighting that organelle positioning and tethering at the nuclear pore provide an unexpected layer of stress regulation.

cell biology↗

bioRxiv2024

Bioinformatics analysis of the potential biomarkers of Multiple Sclerosis and Guillain-Barre syndrome

Recent research emphasizes the intricate interplay of genetics and epigenetics in neurological disorders, notably Multiple Sclerosis (MS) and Guillain-Barre Syndrome (GBS), both of which exhibit cardiovascular dysregulation, with GBS often featuring serious bradyarrhythmias requiring prompt recognition and treatment. While cardiovascular autonomic dysfunction in MS is typically less severe, orthostatic intolerance affects around half of MS patients. Their distinction lies in their autoimmune responses, MS is an autoimmune disease affecting the central nervous system, causes demyelination and axon damage, leading to cognitive, ocular, and musculoskeletal dysfunction. In contrast, GBS primarily affects the peripheral nervous system, resulting in paralysis and respiratory complications. Despite their differences, both diseases share environmental risk factors such as viral infections and Vitamin D deficiency. This study aims to explore shared gene expression pathways, functional annotations, and molecular pathways between MS and GBS to enhance diagnostics, pathogenesis understanding, and treatment strategies through molecular analysis techniques. Through the gene expression analysis, five significant genes were found UTS2, TNFSF10, GBP1, VCAN, FOS. Results shows that Common DEGs are linked to apoptosis, bacterial infections, and atherosclerosis. Molecular docking analysis suggests Aflatoxin B1 as a potential therapeutic compound due to its high binding affinity with common differentially expressed proteins.

bioinformatics↗

bioRxiv2022

Helicobacter pylori vacuolating cytotoxin A exploits human endosomes for intracellular activation

Helicobacter pylori infection is the main cause of gastric cancer. Vacuolating cytotoxin A (VacA) is a H. pylori pore-forming toxin and a key determinant of gastric cancer risk. VacA is secreted as an 88-kDa polypeptide (p88) that upon interaction with host cells induces cytotoxic effects, including cell vacuolation and mitochondrial dysfunction. These effects are currently believed to be due to VacA p88 accumulating inside host cells and forming oligomeric anion-specific channels in membranes of intracellular compartments. However, the molecular nature of intracellular VacA channels in host cells remains undefined. Here we show that VacA p88 does not accumulate inside human epithelial cells, but instead is rapidly processed in endosomes into smaller p31/p28 and p37 products in a manner that precedes VacA-induced vacuolation. VacA processing requires endosomal acidification and concerted cleavage by multiple endo-lysosomal proteases including cathepsins. In situ structural mapping reveals that upon processing, the toxins central hydrophilic linker and globular C-terminus are excised, whereas oligomerization determinants are retained. Congruently, the processed products are constituents of a high-molecular-weight complex inside the host cell [boxh] which we propose is the intracellular, mature and active VacA pore. These findings suggest that VacA exploits human endosomes for proteolytic processing and intracellular activation. Significance StatementHelicobacter pylori is a cancer-causing bacterium that infects the stomach of billions of people worldwide. Vacuolating cytotoxin A (VacA) is an important H. pylori virulence factor and its activity directly correlates with gastric carcinogenesis. Yet despite decades of intense research, the mechanisms underlying VacA activity in human cells remain incompletely understood. Here, we present evidence suggesting that VacA is activated inside human cells by multi-step proteolytic processing involving endo-lysosomal proteases including cathepsins. We also track and identify the functional processed VacA isoforms in host cells. These results revolutionize our understanding of the mechanism of VacA activation in human cells, whilst expanding our knowledge of the diversity of microbial virulence factors that exploit human endo-lysosomes for pathogenesis.

molecular biology↗

bioRxiv2019

Three dimensional nanoscopy of whole cells and tissues with in situ point spread function retrieval

Single-molecule localization microscopy is a powerful tool in visualizing organelle structures, interactions, and protein functions in biological research. However, whole-cell and tissue specimens challenge the achievable resolution and depth of nanoscopy methods. As imaging depth increases, photons emitted by fluorescent probes, the sole source of molecular positions, were scattered and aberrated, resulting in image artifacts and rapidly deteriorating resolution. We propose a method to allow constructing the in situ 3D response of single emitters directly from single-molecule dataset and therefore allow pin-pointing single-molecule locations with limit-achieving precision and uncompromised fidelity through whole cells and tissues. This advancement expands the routine applicability of super-resolution imaging from selected cellular targets near coverslips to intra- and extra-cellular targets deep inside tissues. We demonstrate this across a range of cellular-tissue architectures from mitochondrial networks, microtubules, and nuclear pores in 2D and 3D cultures, amyloid-{beta} plaques in mouse brains to developing cartilage in mouse forelimbs.

biophysics↗

bioRxiv2019

Shake-it-off: A simple ultrasonic cryo-EM specimen preparation device

Although microscopes and image analysis software for electron cryomicroscopy (cryo-EM) have improved dramatically in recent years, specimen preparation methods have lagged behind. Most strategies still rely on blotting microscope grids with paper to produce a thin film of solution suitable for vitrification. This approach loses more than 99.9% of the applied sample and requires several seconds, leading to problematic air-water interface interactions for macromolecules in the resulting thin film of solution and complicating time-resolved studies. Recently developed self-wicking EM grids allow use of small volumes of sample, with nanowires on the grid bars removing excess solution to produce a thin film within tens of milliseconds from sample application to freezing. Here we present a simple cryo-EM specimen preparation device that uses components from an ultrasonic humidifier to transfer protein solution onto a self-wicking EM grid. The device is controlled by a Raspberry Pi single board computer and all components are either widely available or can be manufactured by online services, allowing the device to be constructed in laboratories that specialize in cryo-EM, rather than instrument design. The simple open-source design permits straightforward customization of the instrument for specialized experiments.\n\nSynopsisA method is presented for high-speed low-volume cryo-EM specimen preparation with a device constructed from readily available components.

biophysics↗

bioRxiv2017

Thoracolumbar Intervertebral Disc Area Morphometry In Elderly Chinese Men And Women: Radiographic Quantifications At Baseline And Changes At Year-4 Follow-Up

The manuscript submitted does not contain information about medical device(s)/drug(s). No benefits in any form have been or will be received from a commercial party related directly or indirectly to the subject of this manuscript.\n\nStudy DesignA population-based radiographic study with longitudinal follow-up.\n\nObjectiveTo develop a quantitative index for lumbar disc space narrowing (DSN) evaluation in elderly subjects; to determine how DSN in the elderly is influenced by osteoporosis and gender.\n\nSummary of Background DataThere is paucity of research on quantitative classification of lumbar DSN based on disc areal morphometry.\n\nMethodsWith the database of Osteoporotic Fractures in Men (Hong Kong) and Osteoporotic Fractures in Women (Hong Kong) Studies and those who attended the year-4 follow-up (n = 1519 for men and n = 1546 for women), data of 491 women and 592 men were randomly selected. The anterior, middle, and posterior heights, anteroposterior diameter and area of intervertebral discs (T4T5 to L4L5) were measured on lateral radiographs. Disc Area Index for Lumbar Spine (DAIL, disc area divided by the mean of the sum of square of the adjacent upper and lower vertebrae mid-height anterior-posterior diameter) was developed and compared with semi-quantitative DSN expert grading.\n\nResultsDAIL correlated with semi-quantitative grading, with sensitivity and specificity varying from 87.3% to 96.8% for grade-1 DSN (<30% reduction in disc height), and 92.9 % to 100% for grade-3 DSN (>60% reduction in disc height). The thoracolumbar disc area loss among men and women during 4-years follow-up period varied between 1.32% and 3.56%, and it was greater for women (mean: 2.44%) than for men (mean: 1.90%, p=0.044). Majority of lumbar DSN progressions during 72 to 76 years old were progression from normal disc space to grade-1DSN. Osteoporosis was associated with greater disc area decrease, both for thoracic and lumbar discs.\n\nConclusionLumbar DSN can be quantified using DAIL. In elderly Chinese, intervertebral disc narrowing over a 4-year period was greater in women than men, and associated with the presence of osteoporosis.

epidemiology↗