Biology subjects

Hart, M. L.

Publications and source records attributed to Hart, M. L..

5 recordsLinked to original sources

bioRxiv2026

Functional partitioning of lipoic acid decouples cellular abundance from mitochondrial utilization

-Lipoic acid (LA) is widely included in "mitochondrial cocktails" recommended to patients with primary mitochondrial disorders, yet its mechanism of action remains unclear. Here, we define the intracellular availability and functional utilization of LA in mammalian cells. We show that LA exists in two functionally distinct cellular pools: a low-abundance free pool and a protein-bound pool generated through mitochondrial fatty acid synthesis (mtFAS). Disruption of the mtFAS pathway abolishes protein lipoylation and impairs oxidative phosphorylation without altering free LA levels. Conversely, supplementation with exogenous LA markedly increases free intracellular LA without restoring protein lipoylation, mitochondrial respiration, or cell proliferation. Instead, the cellular effects of LA supplementation resemble those of the antioxidant N-acetylcysteine. These findings clarify the mechanism of action of a widely used mitochondrial supplement and identify a fundamental disconnect between cellular LA abundance and mitochondrial utilization, challenging the rationale for using LA supplementation to restore mitochondrial function.

biochemistry↗

bioRxiv2026

Adaptive plasticity of aspartate metabolism in succinate dehydrogenase-deficient cancer cells

Succinate dehydrogenase (SDH) supports cancer cell proliferation by enabling oxidative biosynthesis of the amino acid aspartate, yet SDH loss can also drive tumorigenesis. To cope with SDH loss, cancer cells can engage alternative aspartate synthesis pathways; however, the variables dictating pathway usage and adaptive mechanisms involved are incompletely understood. Here, we systematically profile the adaptation of SDH-knockout cancer cells and find that cells can adapt to SDH loss via at least two distinct mechanisms: suppression of respiratory complex I or upregulation of pyruvate carboxylase. Each route gives rise to distinct metabolic states with both shared and unique dependencies, but either route allows cells to overcome aspartate limitation, improve proliferative fitness, and mitigate pyrimidine-dependent replication stress. Overall, this work provides a comprehensive view of adaptive aspartate synthesis in SDH-deficient cancer cells, highlights a remarkable redox-constrained metabolic plasticity, and nominates potential metabolic vulnerabilities likely to be shared among SDH-deficient cancer cells.

cancer biology↗

bioRxiv2025

Succinate Dehydrogenase loss causes cascading metabolic effects that impair pyrimidine biosynthesis

Decreased availability of the amino acid aspartate can constrain cell function in diverse biological contexts, but the temporal interplay between aspartate, downstream metabolic changes, and functional effects remains poorly understood. Using an aspartate biosensor and live-cell imaging, we examine the interaction between aspartate abundance and cell proliferation in several models of aspartate limitation. While aspartate deficiencies intuitively interface with proliferation in some contexts, aspartate limitation from succinate dehydrogenase (SDH) inhibition causes strikingly nonintuitive dynamics resulting from an outsized impairment of pyrimidine synthesis. Mechanistically, we find that SDH loss impairs pyrimidine biosynthesis by decreasing aspartate and accumulating succinate, which competitively inhibits mammalian aspartate transcarbamylase (ATCase). This metabolic interaction persists in multiple models of SDH deficiency, causing pyrimidine insufficiency, replication stress, and sensitivity to ATR kinase inhibition. These findings define a novel role for succinate in modulating cellular nucleotide homeostasis, suggest a potential therapeutic vulnerability of SDH-deficient tumors, and demonstrate how cascading metabolic interactions can unfold to impact cell function.

cell biology↗

bioRxiv2022

Mitochondrial Redox Adaptations Enable Aspartate Synthesis in SDH-deficient Cells

The oxidative tricarboxylic acid (TCA) cycle is a central mitochondrial pathway integrating catabolic conversions of NAD+ to NADH and anabolic production of aspartate, a key amino acid for cell proliferation. Several TCA cycle components are implicated in tumorigenesis, including loss of function mutations in subunits of succinate dehydrogenase (SDH), also known as complex II of the electron transport chain (ETC). Mechanistic understanding of how proliferating cells tolerate the metabolic defects of SDH loss is still lacking. Here, we identify that SDH supports cell proliferation through aspartate synthesis but, unlike other ETC impairments, is not restored by electron acceptor supplementation. Interestingly, we find aspartate production and cell proliferation are restored to SDH impaired cells by concomitant inhibition of ETC complex I (CI). We determine that the benefits of CI inhibition in this context are dependent on decreasing mitochondrial NAD+/NADH, which drives SDH-independent aspartate production. We also find that genetic loss or restoration of SDH selects for cells with concordant CI activity, establishing distinct modalities of mitochondrial metabolism for maintaining aspartate synthesis. Collectively, these data identify a metabolically beneficial mechanism for CI loss in proliferating cells and reveal that compartmentalized redox changes can impact cellular fitness.

biochemistry↗

bioRxiv2020

Gut Dysbiosis with a Pathobiont Shifts the Intestinal Microbiota Profile and Accelerates Lupus Nephritis

The gut microbiota (GM) exerts a strong influence over the host immune system and dysbiosis of this microbial community can affect the clinical phenotype in chronic inflammatory conditions. To explore the role of the GM in lupus nephritis, we colonized NZM2410 mice with Segmented Filamentous Bacteria (SFB). Gut colonization with SFB was associated with worsening glomerulonephritis, glomerular and tubular immune complex deposition and interstitial inflammation compared to NZM2410 mice free of SFB. With SFB colonization mice experienced an increase in small intestinal lamina propria Th17 cells and group 3 innate lymphoid cells (ILC3s). However, although serum IL-17A expression was elevated in these mice, Th17 cells and ILC3s were not detected in the inflammatory infiltrate in the kidney. In contrast, serum and kidney tissue expression of the macrophage chemoattractants MCP-1 and CXCL1 were significantly elevated in SFB colonized mice. Furthermore, kidney infiltrating F4/80+CD206+ M2-like macrophages were significantly increased in these mice. Evidence of increased gut permeability or "leakiness" was detected in SFB colonized mice. Finally, the intestinal microbiome of SFB colonized mice at 15 and 30 weeks of age exhibited dysbiosis when compared to uncolonized mice at the same time points. Both microbial relative abundance as well as biodiversity of colonized mice was found to be altered. Collectively, SFB gut colonization in the NZM2410 mouse exacerbates kidney disease, promotes kidney M2-like macrophage infiltration and overall intestinal microbiota dysbiosis.

immunology↗