Biology subjects

Vartak, N.

Publications and source records attributed to Vartak, N..

3 recordsLinked to original sources

bioRxiv2023

RAB18 confers protection to lipid droplets from lysolipophagy and counters cellular steatosis

Lipid droplet (LD) enlargement is the most conspicuous cellular phenotype of steatotic liver diseases such as NAFLD and NASH. The small GTPase RAB18 localizes to lipid droplets yet its effects on LD dynamics are unknown. We show that RAB18 localizes to LDs dynamically via the acylation cycle in an activity dependent manner. Removal of RAB18 from LDs through acylation cycle inhibition of RNAi-mediated downregulation leads to an increase in LD size, that can be prevented by inhibition of autophagy. We propose a model where RAB18 on LDs decreases the susceptibility of LDs to autophagy by lysosomes, allowing them to exist longer in cells and enabling an even distribution of exogenous lipid load. In the absence of RAB18, fewer LDs survive autophagic removal, and enlarge disproportionately as they absorb the incumbent exogenous lipid load on cells - leading to cellular steatosis. Inhibition of autophagy prevented cellular steatosis in primary human hepatocytes. Finally, mice treated with the autophagy inhibitor chloroquine were resistant to the development of liver steatosis when on a steatogenic diet. The modulation of RAB18 activity and autophagy inhibition represents a promising approach to prevent steatotic liver disease in the clinical setting. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=112 SRC="FIGDIR/small/531838v1_ufig1.gif" ALT="Figure 1"> View larger version (52K): org.highwire.dtl.DTLVardef@57d8f8org.highwire.dtl.DTLVardef@165ad0aorg.highwire.dtl.DTLVardef@43964corg.highwire.dtl.DTLVardef@140746f_HPS_FORMAT_FIGEXP M_FIG C_FIG One line summaryRAB18 prevents lipid droplet autophagy to distribute lipid load in cells and prevent steatosis.

cell biology↗

bioRxiv2021

The repeat region of the circumsporozoite protein is an elastic linear spring with a functional role in Plasmodium sporozoite motility

The circumsporozoite protein (CSP) forms a dense coat on the surface of the sporozoite, the infective stage of the malaria parasite. The central repeat region of CSP is a critical component of the only licensed malaria vaccine yet little is known about its structure or function. We found that sporozoite mutants with severely truncated or scrambled repeats have impaired motility due to altered adhesion site formation and dynamics, suggesting that the CSP repeats provide a cohesive environment in which adhesion sites can form. We hypothesized that biophysical properties of the repeats are important in this role and interrogated this using single-molecule fluorescence-force spectroscopy. We show that the repeats are a stiff, linear spring with elastic properties, dependent upon length and lost when the repeats are scrambled. These data are the first evidence that the CSP repeat region serves a functional role during infection and motility, likely mediated through its biophysical properties. SummaryNo clear function of the central repeat region of the malaria circumsporozoite protein has been described to date, despite its central role in the only licensed malaria vaccine. Here we use mutational analysis and single-molecule fluorescence-force spectroscopy to describe the structural properties and determine the function of this conserved region and important vaccine target. HighlightsThe CSP repeats have properties of a linear spring Scrambling or large truncations of the repeats leads to defects in sporozoite motility Motility defects are attributed to abnormal formation of adhesion sites

microbiology↗

bioRxiv2019

Intravital multi-modal flux analysis reveals the transport mechanism of bile acids through hepatic microconduits

Small-molecule flux in tissue-microdomains is essential for organ function, but knowledge of this process is scant due to the lack of suitable methods. We developed two independent techniques that allow the quantification of advection (flow) and diffusion in individual bile canaliculi and in interlobular bile ducts of intact livers in living mice, namely Fluorescence Loss After Photoactivation (FLAP) and Intravital Arbitrary Region Image Correlation Spectroscopy (IVARICS). The results challenge the prevailing ‘mechano-osmotic’ theory of canalicular bile flow. After active transport across hepatocyte membranes bile acids are transported in the canaliculi primarily by diffusion. Only in the interlobular ducts, diffusion is augmented by regulatable advection. Photoactivation of fluorescein bis-(5-carboxymethoxy-2-nitrobenzyl)-ether (CMNB-caged fluorescein) in entire lobules demonstrated the establishment of diffusive gradients in the bile canalicular network and the sink function of interlobular ducts. In contrast to the bile canalicular network, vectorial transport was detected and quantified in the mesh of interlobular bile ducts. In conclusion, the liver consists of a diffusion dominated canalicular domain, where hepatocytes secrete small molecules and generate a concentration gradient and a flow-augmented ductular domain, where regulated water influx creates unidirectional advection that augments the diffusive flux.One Sentence Summary/Keywords Bile flux proceeds by diffusion in canaliculi, augmented by advection in ducts.Competing Interest StatementThe authors have declared no competing interest.View Full Text

physiology↗