Biology subjects

Martin, M. G.

Publications and source records attributed to Martin, M. G..

6 recordsLinked to original sources

bioRxiv2026

Calcineurin B-mediated Ca2+ sensing translates stress signal intensity into the assembly of phase-separated condensates at PERK complexes.

Endoplasmic reticulum (ER) stress activates protein kinase RNA-like ER kinase (PERK), which initially promotes adaptive responses but remains the only active UPR branch during prolonged stress, mediating both early cytoprotective and chronic pro-apoptotic signaling. Recently, we identified translocon-generated Ca2+ microdomains that promote PERK phosphorylation during early UPR, revealing a mechanism by which local Ca2+ signals regulate UPR activation. However, the molecular mechanism linking these Ca2+ microdomains to PERK activation remains elusive. Previously, we showed that calcineurin (CN), a Ca2+ -dependent heterodimer composed of catalytic (CNA) and regulatory (CNB) subunits, exerts a non-canonical pro-survival function by promoting PERK autophosphorylation. Here, using super-resolution microscopy, CRISPR-Cas9 editing, in silico analyses, and optogenetic droplet assays, we identify CNB as a local Ca2+ sensor that couples translocon-generated Ca2+ signals to liquid condensate assembly, thereby promoting adaptive PERK phosphorylation. These findings establish CNB-mediated condensate assembly as a mechanism that translates local Ca2+ signals into spatially organized early adaptive PERK signaling.

cell biology↗

bioRxiv2024

Extensive PFAS accumulation by human gut bacteria

Per- and polyfluoroalkyl Substances (PFAS) - the so-called forever chemicals - are a major cause of environmental and health concern due to their toxicity and long-term persistence1,2. Yet, no efficient mechanisms for their removal have been identified. Here we report bioaccumulation of PFAS by several gut bacterial species over a wide range of concentrations from nanomolar up to 500 M. For bioaccumulating Bacteroides uniformis, a highly prevalent species, we estimate intracellular PFAS concentration in the mM range - above that of most native metabolites. Despite this high bioaccumulation, B. uniformis cells could grow appreciably up to 250 M perfluorononanoic acid (PFNA) exposure. Escherichia coli, which accumulated PFAS to a much lesser extent, substantially increased PFAS bioaccumulation when lacking TolC efflux pump indicating trans-membrane transport in PFAS bioaccumulation. Electron microscopy and cryogenic Focused Ion Beam-Secondary Ion Mass-spectrometry revealed distinct morphological changes and intracellular localisation of PFNA aggregates. Bioaccumulation of PFAS and transmembrane transport is also evident in proteomics, metabolomics, thermal proteome profiling, and mutations following adaptive laboratory evolution. In an in vivo context, mice colonized with human gut bacteria showed, compared to germ-free controls or those colonized with low-bioaccumulating bacteria, higher PFNA levels in excreted feces. As the gut microbiota is a critical interface between exposure and human body, our results have implications for understanding and utilizing microbial contribution to PFAS clearance.

microbiology↗

bioRxiv2023

Impaired cholesterol transport from aged astrocytes to neurons can be rescued by cannabinoids.

Cholesterol is crucial for the proper functioning of eukaryotic cells, especially neurons, which rely on cholesterol to maintain their complex structure and facilitate synaptic transmission. However, brain cells are isolated from peripheral cholesterol by the blood-brain barrier and mature neurons primarily uptake the cholesterol synthesized by astrocytes for proper function. This study aimed to investigate the effect of aging on cholesterol trafficking in astrocytes and its delivery to neurons. Using in vitro and in vivo models of aging, we found that aged astrocytes accumulated high levels of cholesterol in the lysosomal compartment, and this cholesterol buildup can be attributed to the simultaneous occurrence of two events: decreased levels of the ABCA1 transporter which impairs ApoE-cholesterol export from astrocytes, and reduced expression of NPC1, which hinders cholesterol release from lysosomes. We show that these two events are accompanied by increased microR33 in aged astrocytes, which is known to downregulate ABCA1 and NPC1. In addition, we demonstrate that the microR33 increase is triggered by oxidative stress, one of the hallmarks of aging. By co-culture experiments we also show that aging in vitro impairs the cholesterol delivery from astrocytes to neurons. Remarkably, we found that this altered transport of cholesterol could be alleviated through treatment with endocannabinoids as well as cannabidiol or CBD. Given that reduced neuronal cholesterol affects synaptic plasticity, the ability of cannabinoids to restore cholesterol transport from aged astrocytes to neurons holds significant implications in the field of aging.

neuroscience↗

bioRxiv2023

Aster-dependent non-vesicular transport facilitates dietary cholesterol uptake

Intestinal cholesterol absorption is an important contributor to systemic cholesterol homeostasis. Niemann-Pick C1 Like 1 (NPC1L1), the target of the drug ezetimibe (EZ), assists in the initial step of dietary cholesterol uptake. However, how cholesterol moves downstream of NPC1L1 is unknown. Here we show that Aster-B and Aster-C are critical for non-vesicular cholesterol movement in enterocytes, bridging NPC1L1 at the plasma membrane (PM) and ACAT2 in the endoplasmic reticulum (ER). Loss of NPC1L1 diminishes accessible PM cholesterol in enterocytes and abolishes Aster recruitment to the intestinal brush border. Enterocytes lacking Asters accumulate cholesterol at the PM and display evidence of ER cholesterol depletion, including decreased cholesterol ester stores and activation of the SREBP-2 transcriptional pathway. Aster-deficient mice have impaired cholesterol absorption and are protected against diet-induced hypercholesterolemia. Finally, we show that the Aster pathway can be targeted with a small molecule inhibitor to manipulate dietary cholesterol uptake. These findings identify the Aster pathway as a physiologically important and pharmacologically tractable node in dietary lipid absorption. One-Sentence SummaryIdentification of a targetable pathway for regulation of dietary cholesterol absorption

physiology↗

bioRxiv2019

A Holistic Analysis of the Intestinal Stem Cell Niche Network

Although many studies into the intestinal stem cell (ISC) niche have been carried out, they have focused on the role of a single cell type or molecular signal. However, no holistic comparisons of the predominant cell types and signals present within the intestinal mucosa have been conducted to date. We utilize bulk RNA sequencing to profile 20 different mucosal cell types covering four major cell categories: epithelial, stromal, endothelial and immune. We further examined the stromal signaling environment using scRNAseq to provide a more comprehensive view of the signaling microenvironment within the intestinal mucosa. We identified the primary signals for the major ISC regulatory pathways and their respective cellular sources. Our analysis suggests that a niche network exists, with no single cell type being responsible for ISC self-renewal, proliferation, or differentiation; rather, each cell type within the network carries out specific functions in a highly cooperative and coordinated manner.

cell biology↗

bioRxiv2017

Bioengineered intestinal muscularis complexes with long-term spontaneous and periodic contractions

Although critical for studies of gut motility and intestinal regeneration, the in vitro culture of intestinal muscularis with peristaltic function remains a significant challenge. Periodic contractions of intestinal muscularis result from the coordinated activity of smooth muscle cells (SMC), the enteric nervous system (ENS), and interstitial cells of Cajal (ICC). Reproducing this activity requires the preservation of all these cells in one system. Here we report the first serum-free culture methodology that consistently maintains spontaneous and periodic contractions of murine and human intestinal muscularis cells for months. In this system, SMC expressed the mature marker myosin heavy chain, and multipolar/dipolar ICC, uniaxonal/multipolar neurons and glial cells were present. Furthermore, drugs affecting ENS, ICC or SMC altered the contractions. Combining this method with scaffolds, contracting cell sheets were formed with organized architecture. With the addition of intestinal epithelial cells, this platform enabled at least 9 types of cells from mucosa and muscularis to coexist and function. The method constitutes a powerful tool for mechanistic studies of gut motility disorders and the regeneration of full-thickness engineered intestine.\n\nIn the small intestine, the mucosa processes partially digested food and absorbs nutrients while the muscularis actuates the peristaltic flow to transport luminal content aborally. Gut motility is central to its digestive and absorptive function. The intestinal muscularis contains various types of cells: of these, smooth muscle cells, the enteric nervous system (ENS)1,2, and the pacemaker interstitial cells of Cajal (ICC)3 are three important players involved in the development of gut motility. Recent studies on intestinal tissue engineering have highlighted the importance of regenerating the functional intestinal muscularis4-9. A variety of systems derived from different cell sources, including pluripotent stem cells (PSC)4-6, embryonic stem cells (ESC)7 and primary tissue8,9, have been established to accomplish this goal and different contractile activities were developed in these systems. Notably, spontaneous contractions have been generated in culture systems that contained both ICC and smooth muscle cells4,6,10-13. In addition, electrical-induced neurogenic contractions were also successfully produced4,5,8 when ENS was introduced into culture. In one of the most recent studies, both spontaneous contractions and electrical-induced neurogenic contractions were developed in a PSC-based culture system4.

bioengineering↗