Biology subjects

Kory, N.

Publications and source records attributed to Kory, N..

8 recordsLinked to original sources

bioRxiv2026

Mitochondrial amino acid export preserves mitochondrial volume at the egg-to-embryo transition

In animals, the transition from egg to embryo marks a rapid shift in cellular physiology, yet how mitochondria adapt to support this conversion remains poorly understood. We performed a targeted RNAi screen of conserved, nuclear-encoded mitochondrial proteins in Drosophila melanogaster to identify maternal effects. We identified distinct phenotypic classes affecting mitochondrial distribution or morphology in early embryos. We focused on Sideroflexin-1/3 (Sfxn1-3), a conserved mitochondrial inner membrane transporter, because it uniquely affects embryonic mitochondrial morphology. Maternal loss of Sfxn1-3 causes striking mitochondrial enlargement in embryos but not in oocytes, placing the trigger at the egg-to-embryo transition. Combining mitochondrial immunopurification with LC/MS-based metabolomic profiling, we show that amino acids are markedly enriched in Sfxn1-3-deficient mitochondria in both oocytes and embryos. This accumulation developmentally uncouples the metabolic and morphological phenotypes. By selectively disrupting discrete steps of egg activation, including translational activation, cell cycle re-entry, and fertilization, we demonstrate that mitochondrial swelling is independent of each, prompted instead by egg hydration. Beyond its reported role in proliferating cells as a serine importer, our data support a role for germline Sfxn1-3 in regulating inner mitochondrial membrane permeability to osmotically active amino acids. This activity is crucial for preserving organelle volume during the osmotic challenge of oocyte hydration. When this export fails, amino acid accumulation amplifies osmotic stress and drives rapid mitochondrial swelling. Together, these findings identify mitochondrial inner membrane permeability to amino acids as a key regulatory step that couples pre-established metabolite compartmentalization to osmotic adaptation at egg activation, and reveal how mitochondrial metabolic integrity and volume control are coordinated at this critical developmental transition.

developmental biology↗

bioRxiv2026

Molecular basis of mitochondrial leucine transport by human Sideroflexin 1

Leucine is a central nutrient signal and a ketogenic amino acid that fuels metabolism, yet how it is imported into mitochondria remains incompletely defined. Sideroflexins are conserved inner mitochondrial membrane proteins implicated in amino acid transport, but their mechanism and substrate specificity remain unclear. Using cryogenic electron microscopy, we determined the structure of SFXN1 in its matrix-open conformation. AlphaFold and Boltz co-folding of SFXN1 with a library of human metabolites identified leucine as a candidate substrate, findings supported by thermal stability measurements and mitochondrial transport assays. Comparison with a cytoplasmic-open-model reveals an alternating-access "toggle-switch" mechanism of transport. Together, these findings uncover the molecular basis of leucine transport by SFXN1 and provide a framework for understanding its role in metabolism and disease.

Molecular Biology↗

bioRxiv2025

Inhibition of formate production blocks CD8+ T-cell responses and delays disease onset in a mouse model of type 1 diabetes

The one-carbon metabolic pathway is essential for proliferating cells and has recently been identified as an immunomodulatory target in CD4 T cells. However, its role in other immune cell types has not been fully established. We investigated the function of the one-carbon pathway in CD8 T cells, which are the primary effectors responsible for the destruction of pancreatic beta cells that causes type 1 diabetes. Enzymes involved in the one-carbon pathway, as well as levels of formate--a critical intermediate--were upregulated during CD8 T-cell activation. Pharmacological inhibition of MTHFD2, a mitochondrial enzyme involved in one-carbon metabolism, suppressed CD8 T-cell activation, proliferation, and effector function. Mechanistically, this effect was mediated by reduced signaling through KRAS and the mTORC1 downstream targets HIF1, S6, and STAT3. As previously shown in CD4 T cells, formate supplementation reversed the effects of MTHFD2 inhibition on activation, proliferation, and function of CD8+ T cells, and prevented the reduction of the TCF1high CD8 progenitor cell population, which has been shown to drive anti-beta cell autoimmunity. Formate levels were elevated in the immune cells isolated from pancreatic lymph nodes during the insulitis stage in non-obese diabetic mice. Treatment of euglycemic non-obese diabetic mice with an MTHFD2 inhibitor during the insulitis stage delayed CD8 T-cell infiltration into pancreatic islets and postponed the onset of type 1 diabetes. These findings reveal a new paradigm for preventing and delaying the onset of type 1 diabetes.

immunology↗

bioRxiv2025

Sideroflexins enable mitochondrial transport of polar neutral amino acids

Mitochondria contribute to compartmentalized metabolism in eukaryotic cells, supporting key enzymatic reactions for cell function and energy homeostasis. This compartmentalization necessitates regulated metabolite transport across mitochondrial membranes. While many transport proteins have been identified, several mitochondrial transporters remain poorly characterized. Among these are sideroflexins, an evolutionarily conserved family of mitochondrial inner membrane proteins with unclear function. Using CRISPR/Cas9-mediated candidate transporter knockouts coupled with assessment of mitochondrial membrane permeability via a swelling assay, we identify SFXN1, previously implicated in mitochondrial serine transport and iron homeostasis, as an enabler of mitochondrial transport of multiple neutral amino acids, including proline, glycine, threonine, taurine, hypotaurine, {beta}-alanine, and {gamma}-aminobutyric acid (GABA). We further show that SFXN paralogues exhibit substrate-dependent functional overlap, with SFXN2 and SFXN3 partially rescuing loss of SFXN1 function in glycine-related phenotypes, while SFXN2 and SFXN5 partially rescue SFXN1-dependent changes in enabling GABA transport and metabolism. Altogether, these data establish sideroflexins as key regulators of mitochondrial amino acid transport and metabolism.

biochemistry↗

bioRxiv2025

The mitochondrial NAD transporter SLC25A51 is a modulator of beta cell senescence and type 2 diabetes

AbstractNicotinamide adenine dinucleotide (NAD+) is an essential redox cofactor and signaling molecule linked to age-dependent metabolic decline, with its compartmentalization regulated by the mitochondrial carrier SLC25A51. The mechanisms contributing to declining NAD+ levels during aging and the consequences of altered NAD+ homeostasis across tissues are poorly understood. Here, we show that SLC25A51 is upregulated in aging and aging-associated conditions, particularly in senescent cells. In a mouse model of beta-cell senescence, upregulated SLC25A51 was associated with beta-cell identity loss, senescence progression, and a reduced NAD+/NADH ratio. SLC25A51 was elevated following p16INK4a-, replicative-, irradiation-, and H2O2-induced senescence, with NRF2 implicated as a potential transcriptional regulator. Overexpression of SLC25A51, but not a transport-dead mutant, induced senescence factors, while its deletion prevented this effect. Beta-cell-specific deletion of SLC25A51 lowered p16INK4a levels in pancreatic islets, circulating insulin, and glucose levels, improving insulin sensitivity and indicating its role in cellular senescence and the metabolic control of beta-cell function.

cell biology↗

bioRxiv2024

PNPLA3(148M) Promotes Hepatic Steatosis by Interfering with Triglyceride Hydrolysis Through a Gain-of-Function Mechanism

Background & AimsPNPLA3(148M) (patatin-like phospholipase domain-containing protein 3) is the most impactful genetic risk factor for steatotic liver disease (SLD), thus motivating a search for therapeutic modulators of its expression. A key unresolved issue is whether PNPLA3(148M) confers a loss- or gain-of-function. Here we used multiple approaches to further test the hypothesis that PNPLA3 causes steatosis by sequestering ABHD5 (/{beta} hydrolase domain containing protein 5), the cofactor of ATGL (adipose TG lipase), thus limiting mobilization of hepatic triglyceride (TG). MethodsWe quantified the physical interactions between ABHD5 and PNPLA3/ATGL in cultured hepatocytes using NanoBiT complementation assays. Immunocytochemistry was used to compare the relative binding of PNPLA3 and ATGL to ABHD5 and to determine if PNPLA3 must associate with lipid droplets (LDs) to inhibit ATGL. Adenoviruses and adeno-associated viruses were used to express PNPLA3 in liver-specific Atgl-/- mice and ABHD5 in livers of Pnpla3148M/M mice, respectively. We used purified recombinant proteins to compare the TG hydrolytic activities of PNPLA3 and ATGL in the presence and absence of ABHD5. ResultsABHD5 interacted preferentially with PNPLA3 relative to ATGL in cultured hepatocytes and in vitro, with no differences observed between PNPLA3(WT) or PNPLA3(148M). PNPLA3(148M)-associated inhibition of TG hydrolysis required localization of PNPLA3 to LDs and the presence of ATGL. Finally, overexpression of ABHD5 reversed the hepatic steatosis in Pnpla3M/M mice. ConclusionsThese findings support the premise that PNPLA3(148M) promotes hepatic steatosis by accumulating on LDs and inhibiting ATGL-mediated lipolysis in an ABHD5-dependent manner. Our results predict that reducing, rather that increasing PNPLA3 expression will be the best strategy to treat PNPLA3(148M)-associated SLD. Impact and implicationsSteatotic liver disease (SLD) is a common complex disorder associated with both environmental and genetic risk factors. PNPLA3(148M) is the most impactful genetic risk factor for SLD and yet its pathogenic mechanism remains controversial. Here we provide evidence that PNPLA3(148M) promotes triglyceride (TG) accumulation by sequestering ABHD5, thus limiting its availability to activate ATGL. Although the substitution of methionine for isoleucine reduces the TG hydrolytic activity of PNPLA3, the loss-of-function is only indirectly related to the steatotic effect of the variant. Here we provide evidence that PNPLA3(148M) confers a gain-of-function by interfering with ATGL-mediated TG hydrolysis. These findings have implications for the design of potential PNPLA3-based therapies. Reducing, rather than increasing, PNPLA3 levels is predicted to reverse steatosis in susceptible individuals. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=106 SRC="FIGDIR/small/606015v1_ufig1.gif" ALT="Figure 1"> View larger version (19K): org.highwire.dtl.DTLVardef@1dd7acaorg.highwire.dtl.DTLVardef@1a869dborg.highwire.dtl.DTLVardef@1bde743org.highwire.dtl.DTLVardef@99effc_HPS_FORMAT_FIGEXP M_FIG C_FIG HighlightsO_LIABHD5 binds preferentially to PNPLA3 relative to ATGL. C_LIO_LIPNPLA3(WT) and PNPLA3(148M) compete similarly for binding and inhibition of ATGL. C_LIO_LIABHD5 activates the triglyceride lipase activity of PNPLA3, as well as ATGL. C_LIO_LIThe steatotic effect of PNPLA3(148M) requires expression of ATGL. C_LIO_LIOverexpression of ABHD5 can rescue the steatosis associated with PNPLA3(148M). C_LI

cell biology↗

bioRxiv2024

iAAA-mitochondrial protease YME1L1 regulates the degradation of short-lived mitochondrial transporter SLC25A38

Mitochondrial transporters facilitate the exchange of diverse metabolic intermediates across the inner mitochondrial membrane, ensuring an adequate supply of substrates and cofactors to support redox and biosynthetic reactions within the mitochondrial matrix. However, the regulatory mechanisms governing the abundance of these transporters, crucial for maintaining metabolic compartmentalization and mitochondrial functions, remain poorly defined. Through analysis of protein half-life data and mRNA-protein correlations, we identified SLC25A38, a mitochondrial glycine transporter, as a short- lived protein with a half-life of 4 hours under steady-state conditions. Pharmacological inhibition and genetic depletion of various cellular proteolytic systems revealed that SLC25A38 is rapidly degraded by the iAAA-mitochondrial protease YME1L1. Depolarization of the mitochondrial membrane potential induced by the mitochondrial uncoupler carbonyl cyanide m-chlorophenylhydrozone prevented the degradation of SLC25A38. This dual regulation of SLC25A38 abundance by YME1L1 and mitochondrial membrane potential suggests a link between SLC25A38 turnover, the integrity of the inner mitochondrial membrane, and electron transport chain function. These findings open avenues for investigating whether mitochondrial glycine import coordinates with mitochondrial bioenergetics.

cell biology↗

bioRxiv2020

MCART1 is required for mitochondrial NAD transport

The nicotinamide adenine dinucleotide (NAD+/NADH) pair is a cofactor in redox reactions and is particularly critical in mitochondria as it connects substrate oxidation by the tricarboxylic acid (TCA) cycle to ATP generation by the electron transport chain (ETC) and oxidative phosphorylation. While a mitochondrial NAD+ transporter has been identified in yeast, how NAD enters mitochondria in higher eukaryotes is unknown. Here, we mine gene essentiality data from human cell lines to identify MCART1 (SLC25A51) as co-essential with ETC components. MCART1-null cells have large decreases in TCA cycle flux, mitochondrial respiration, ETC complex I activity, and mitochondrial levels of NAD+ and NADH. Isolated mitochondria from cells lacking or overexpressing MCART1 have greatly decreased or increased NAD uptake in vitro, respectively. Moreover, MCART1 and NDT1, a yeast mitochondrial NAD+ transporter, can functionally complement for each other. Thus, we propose that MCART1 is the long sought mitochondrial transporter for NAD in human cells.

cell biology↗