Biology subjects

Obi, P.

Publications and source records attributed to Obi, P..

3 recordsLinked to original sources

bioRxiv2026

Plasma-derived extracellular vesicles as potential biomarkers and mediators of functional alterations in MELAS

Mitochondrial encephalomyopathy, lactic acidosis and stroke-like episodes (MELAS) syndrome is a genetic disorder characterized by progressive neuromuscular and multisystem symptoms. MELAS typically manifests during childhood, can be difficult to diagnose, and has no cure. Extracellular vesicles (EVs) are lipid-enclosed nanoparticles secreted from cells that contain biological cargo and have demonstrated potential as biomarkers. We investigated the potential of plasma-derived EVs as diagnostic biomarkers of MELAS and examined their functional effects on mitochondrial respiration in treated skeletal muscle myotubes. Plasma-derived EVs were isolated from MELAS patients and age- and sex-matched control individuals, and biophysical characteristics and cargo of EVs analyzed. A Mito Stress Test was performed to assess oxygen consumption rate (OCR) in healthy myotubes treated with Control- or MELAS-EVs to determine the functional effects of circulatory EVs. Nine MELAS patients from two families were studied, and the results were categorized by age, sex and mtDNA heteroplasmy level. EV size and zeta potential remained unchanged. However, total EV concentration was higher in MELAS patients, particularly for small-EVs (<200 nm) and in younger patients (<25 years old). Relative protein yield per EV was lower in the MELAS group, especially among female and younger individuals. EV double-stranded DNA (dsDNA) concentration did not differ between MELAS- and Control-EVs overall, but was higher in male MELAS patients. Protein markers typically enriched in small-EVs showed altered expression in MELAS EVs: TSG101 and CD63 were lower, while flotillin-1 was higher compared to Control-EVs. A decrease in basal OCR was shown in cells treated with MELAS-EVs, with a similar response noted in the group treated with EVs from female MELAS patients. Post-treatment analysis showed no differences in oxidative phosphorylation (OXPHOS) subunit levels between cells treated with MELAS- and Control-EVs. In conclusion, plasma-derived EVs show promise as potential biomarkers for MELAS, and circulating EVs in this patient population may contribute to systemic metabolic dysfunction.

Cell Biology↗

bioRxiv2025

Structural Mechanisms Underlying Distinct Binding and Activities of 18:0 and 18:1 Lysophosphatidic acids at LPA1 Receptor

Lysophosphatidic acids (LPAs) are bioactive lipids that regulate numerous physiological functions in humans. Cell signaling by LPAs is mediated mainly via six LPA receptors (LPA1-6), class A G protein-coupled receptors (GPCRs). Among these, LPA1 is recognized to play an essential role in cell proliferation, survival, migration, and tumorigenesis. Despite the structural similarity, 18:0-LPA and 18:1-LPA exhibit distinct functional responses in cell lines overexpressing LPA1. Specifically, our in vitro studies show that 18:1-LPA induces greater Erk activation than 18:0-LPA in PC-3 human prostate cancer cells. The structural basis underlying this differential receptor activation has not been previously studied. Using classical molecular dynamics and enhanced sampling techniques, we examined the access and binding mechanisms of the two LPA species to the active state LPA1 receptor. The results show that 18:0-LPA and 18:1-LPA adopt distinct and dynamic poses in the orthosteric pocket despite their similar starting configurations. Mainly, the alkyl tails of the ligands exhibit distinct orientations and residue interactions, leading to differential conformational changes in key activation switches on the conserved CWxP and PIF structural motifs of the receptor. Also, there are significant differences in interhelical interactions at the intracellular end of the transmembrane helices 1, 3, 6, and 7. These distinct arrangements lead to striking differences in LPA1 interactions with the G-helix of the heterotrimeric Gi-protein. Notably, 18:0-LPA and 18:1-LPA exhibit similar membrane partitioning characteristics and receptor entry processes through aqueous paths. Our comprehensive in-silico studies offer valuable structural insights into the observed differences in functional responses by 18:0-and 18:1-LPA.

biophysics↗

bioRxiv2024

Structural basis for the access and binding of resolvin D1 (RvD1) to formyl peptide receptor 2 (FPR2/ALX), a class A GPCR

Inflammation is essential to the bodys defense against tissue injury and microbial invasion. However, uncontrolled inflammation is highly detrimental and can result in chronic inflammatory diseases such as asthma, cancer, obesity, and diabetes. An increasing body of evidence suggests that specialized pro-resolving lipid mediators (SPMs), such as resolvins, are actively involved in critical cellular events that drive the resolution of inflammation and a return to homeostasis. An imbalance caused by insufficient SPMs can result in the unsuccessful resolution of inflammation. The D-series resolvins (metabolites of docosahexaenoic acid), such as resolvin D1 (RvD1) and resolvin D2 (RvD2), carry out their pro-resolving functions by directly binding to class A G protein-coupled receptors FPR2/ALXR and GPR32, and GPR18, respectively. We recently demonstrated that RvD1 and RvD2 preferentially partition and accumulate at the polar headgroup regions of the membrane. However, the mechanistic detail of how RvD1 gains access to the FPR2 binding site from a surrounding membrane environment remains unknown. In this study, we used classical MD and well-tempered metadynamics simulations to examine the structural basis for the access and binding of RvD1 to its target receptor from aqueous and membrane environments. The results offer valuable insights into the access path, potential binding pose, and key residue interactions essential for the access and binding of RvD1 to FPR2/ALXR and may help in identifying small molecule therapeutics as a possible treatment for inflammatory disorders.

biophysics↗