Biology subjects

Shin, K. C.

Publications and source records attributed to Shin, K. C..

7 recordsLinked to original sources

bioRxiv2026

GDF3 is an endogenous antagonist of the ActE-ALK7/ACVR2 pathway in adipocytes

Metabolic dysfunction-associated steatotic liver disease (MASLD) and steatohepatitis (MASH) arise, in part, from excessive free fatty acid flux from adipose tissue to the liver. Activin E (ActE, encoded by INHBE) suppresses adipocyte lipolysis through the type I receptor ALK7 (ACVR1C). Loss-of-function variants in INHBE and ACVR1C reduce waist-to-hip ratio in humans, yet genetic knockouts in mice produce insulin resistance and hepatic steatosis, suggesting discrepancies between human and mouse biology. We identify GDF3, a TGF-{beta} superfamily ligand upregulated in obese adipose tissue, as the principal endogenous antagonist of ActE/ALK7 signaling. Human transcriptomic datasets reveal coordinated dysregulation: hepatic INHBE expression and circulating ActE protein are elevated in obesity, while adipose ACVR1C is downregulated and GDF3 is reciprocally upregulated. Using ALK7-selective reporter assays, we show GDF3 inhibits ActE-driven SMAD2/3 signaling as a competitive antagonist rather than the weak agonist previously proposed. ActE suppressed beta-adrenergic-stimulated lipolysis in mouse and human adipocytes and primary human adipose tissue; GDF3 overexpression abolished this effect. In diet-induced obese mice, inducible Gdf3 deletion reduced adipose lipolysis, resolved hepatic steatosis and fibrosis, and improved insulin sensitivity, benefits abolished by Inhbe knockdown, confirming dependence on ActE signaling. Predicted loss-of-function variants in INHBE show only nominal, WHR-dependent associations with type 2 diabetes risk, potentially confounded by hematological effects on HbA1c. Gdf3 deficiency synergized with the clinical-stage anti-activin receptor antibody Bimagrumab to amplify fat-mass loss and improve glucose homeostasis in multiple MASH models. These findings establish GDF3 as an endogenous antagonist of ActE-ALK7 signaling and nominate GDF3 inhibition as a therapeutic strategy for MASLD/MASH.

physiology↗

bioRxiv2025

Synaptotagmin-1 and complexin inhibit spontaneous vesicle fusion by masking PIP2, not by clamping SNARE assembly

Vesicle fusion underlies neurotransmitter release, enabling cellular communication. The rapid kinetics of vesicle fusion, tight docking to the plasma membrane, and coordination by multiple SNARE complexes suggest that SNARE complexes are already pre-assembled before fusion. Synaptotagmin-1 (Syt-1) and complexin (CPLX) have been proposed to clamp SNARE assembly and arrest fusion. However, these models are largely based on studies conducted under low ionic strength and structural analyses utilizing SNARE-Syt-1 chimera conjugates. We propose phosphatidylinositol 4,5-bisphosphate (PIP2) as a critical lipid catalyst that facilitates fusion through electrostatic dehydration. Here we show that neither the C2AB domain of Syt-1 nor CPLX-2 has clamping or inhibitory effect on SNARE assembly. Instead, the C2AB domain and CPLX-2 inhibit Ca2+-independent vesicle fusion by masking PIP2. Our data resolve the long-standing question of increased spontaneous neurotransmitter release in Syt-1 and CPLX knockout neurons, emphasizing PIP2 as an electrostatic lipid catalyst for fusion. One Sentence SummarySyt-1 and complexin inhibit spontaneous fusion by masking PIP2.

neuroscience↗

bioRxiv2025

Seizure-like behavior and hyperactivity in napb knockout zebrafish as a model for autism and epilepsy

We identified N-ethylmaleimide-sensitive factor attachment protein beta (NAPB) as a potential risk gene for autism and epilepsy. Notably, Qatari monozygotic triplets with loss of function mutations in NAPB exhibit early onset epileptic encephalopathy and varying degrees of autism. In this study, we generated NAPB zebrafish model using CRISPR-Cas9-sgRNAs technology for gene editing of the two orthologs napba and napbb. We observed that napb crispants (CR) show shorter motor neuron axons length together with altered locomotion behavior, including significant increases in larvae total distance traveled, swimming velocity, and rotation frequency, indicating that these behavioral changes effectively mimic the human epileptic phenotype. We applied microelectrode array (MEA) technology to monitor neural activity and hyperexcitability in the zebrafish model. The napb CR shows hyperexcitability in the brain region. By combining behavioral tests with electrophysiological MEA assays, the established NAPB zebrafish model can be employed to study the pathophysiological mechanisms of ASD and epilepsy to screen potential therapeutic drugs.

neuroscience↗

bioRxiv2024

Longitudinal cellular and humoral immune responses following Covid-19 BNT162b2-mRNA-based booster vaccination of craft and manual workers in Qatar.

IntroductionIn March 2020, the rapid spread of SARS-CoV-2 prompted global vaccination campaigns to mitigate COVID-19 disease severity and mortality. The 2-dose BNT162b2- mRNA vaccine effectively reduced infection and mortality rates, however, waning vaccine effectiveness necessitated the introduction of a third vaccine dose or booster. To assess the magnitude and longevity of booster-induced immunity, we conducted a longitudinal study of SARS-CoV-2 specific cellular and humoral immune responses among Qatars vulnerable craft and manual worker community. We also investigated the impact of prior naturally acquired immunity on booster vaccination efficacy. MethodsSeventy healthy participants were enrolled in the study, of whom half had prior SARS-CoV-2 infection. Blood samples were collected before and after booster vaccination to evaluate immune responses through SARS- CoV-2 specific ELISpots, IgG ELISA, neutralization assays, and flow cytometric immunophenotyping ResultsT cell analysis revealed increased Th1 cellular responses, marked by enhanced IFN-{gamma} release, in recently infected participants, which was further enhanced by booster vaccination for up to 6-months. Furthermore, booster vaccination stimulated cytotoxic T cell responses in infection-naive participants, characterized by granzyme B production. Both natural SARS-CoV-2 infection and booster vaccination induced robust and durable SARS-CoV-2 specific humoral immune responses, with high neutralizing antibody levels. Prior natural infection was also linked to an increased number of class- switched B cells prior to booster vaccination. ConclusionThese findings underscore the importance of booster vaccination in enhancing anti-viral immunity across both infection-naive and previously infected individuals, enhancing distinct arms of the anti-viral immune response and prolonging naturally acquired immunity.

immunology↗

bioRxiv2023

PIP2 electrostatically triggers vesicle fusion: arresting full SNARE assembly and vesicle fusion by PIP2-masking

SNARE proteins drive vesicle fusion and neurotransmitters release. Given that exocytosis is fast, and vesicle docking is tight, SNARE proteins are likely pre-assembled before fusion. However, the molecular mechanisms of the partially-assembled SNARE complex remain controversial. We use amperometry and the reconstitution of native vesicle fusion to show that MARCKS arrests basal fusion by masking PIP2 in a vesicle docking state where the SNARE complex is partially assembled. Ca2+/CaM or PKC-epsilon unmask PIP2 through the MARCKS dissociation, and thus rescue basal fusion and potentiates synaptotagmin-1-mediated Ca2+-dependent vesicle fusion. Our data provide the novel model that PIP2 electrostatically triggers vesicle fusion by lowering the hydration energy, and that masking PIP2 arrests vesicle fusion in a state of the partial SNARE assembly. Vesicle-mimicking liposomes fail to arrest vesicle fusion by masking PIP2, indicating that native vesicles are essential for the reconstitution of physiological vesicle fusion. One Sentence SummaryMasking PIP2 by MARCKS arrests the full SNARE assembly and vesicle fusion.

neuroscience↗

bioRxiv2022

Deletion of TRPC6, an autism risk gene, induces hyperexcitability in cortical neurons derived from human pluripotent stem cells

Autism spectrum disorder (ASD) is a complex and heterogeneous neurodevelopmental disorder linked to numerous rare, inherited and arising de novo genetic variants. ASD often co-occurs with attention-deficit hyperactivity disorder and epilepsy, which are associated with hyperexcitability of neurons. However, the physiological and molecular mechanisms underlying hyperexcitability in ASD remain poorly understood. Transient receptor potential canonical-6 (TRPC6) is a Ca2+-permeable cation channel that regulates store-operated calcium entry (SOCE) and is a candidate risk gene for ASD. Using human pluripotent stem cell (hPSC)-derived cortical neurons, single cell calcium imaging, and electrophysiological recording, we show that TRPC6 knockout (KO) reduces SOCE signaling and leads to hyperexcitability of neurons by increasing action potential frequency and network burst frequency. Our data provide evidence that reduction of SOCE by TRPC6 KO results in neuronal hyperexcitability, which we hypothesize is an important contributor to the cellular pathophysiology underlying hyperactivity in some ASD.

neuroscience↗

bioRxiv2022

Requirement of cholesterol for calcium-dependent vesicle fusion by stabilizing synaptotagmin-1-induced membrane bending

Cholesterol is essential for neuronal activity and function. Cholesterol depletion in the plasma membrane impairs synaptic transmission. However, the molecular mechanisms by which cholesterol deficiency leads to defects in vesicle fusion remain poorly understood. Here we show that cholesterol is required for Ca2+-dependent native vesicle fusion using the in-vitro reconstitution of fusion and amperometry to monitor exocytosis in chromaffin cells. Purified native vesicles were crucial for the reconstitution of physiological Ca2+-dependent fusion, whereas vesicle-mimicking liposomes failed to reproduce the cholesterol effect. Intriguingly, cholesterol had no effect on membrane binding of synaptotagmin-1, a Ca2+ sensor for ultrafast fusion. Cholesterol stabilizes local membrane bending induced by synaptotagmin-1, thereby lowering the energy barrier for Ca2+-dependent fusion to occur. Our data provide evidence that cholesterol depletion abolishes Ca2+-dependent vesicle fusion by disrupting synaptotagmin-1-induced membrane bending, and suggests that cholesterol is an important lipid regulator for Ca2+-dependent fusion.

neuroscience↗