Biology subjects

Mullett, S. J.

Publications and source records attributed to Mullett, S. J..

8 recordsLinked to original sources

bioRxiv2025

CYB5R4 sustains endothelial proliferation and ischemia-induced angiogenesis by maintaining RRM2-dependent nucleotide balance

Angiogenesis is essential for revascularization in peripheral artery disease (PAD), yet pro-angiogenic therapies remain inconsistent. Here, we identify a cytosolic reductase, CYB5R4, as an intrinsic regulator of endothelial proliferation and ischemia-induced angiogenesis. In mice, global haploinsufficiency or inducible endothelial deletion of Cyb5r4 delayed perfusion recovery after femoral artery ligation and reduced capillary expansion. CYB5R4 is known to promote stearoyl-CoA desaturase (SCD) activity and is required for the de novo synthesis of monounsaturated fatty acids. In human endothelial cells, CYB5R4 silencing impaired proliferation with G1-S arrest that was not rescued by monounsaturated fatty acids and differed from the loss of SCD, indicating an SCD-independent mechanism. RNA sequencing with Bayesian network inference highlighted the ribonucleotide-reductase subunit RRM2 as a key downstream mediator. RRM2 overexpression partially restored proliferation. Integrated untargeted metabolomics and targeted nucleotide quantification revealed an imbalanced nucleotide pool in CYB5R4-deficient cells. These findings support a model in which CYB5R4 sustains endothelial proliferation and ischemia-driven angiogenesis by maintaining RRM2-dependent nucleotide balance. Targeting the CYB5R4-RRM2 axis may improve therapeutic angiogenesis in PAD.

molecular biology↗

bioRxiv2025

Reversible Dissociation of Mitochondrial Complex V Balances Anabolic and Energy-Generating Needs in Cancer

Cancer cell metabolic re-programming provides the excess energy and anabolic precursors necessary to sustain uncontrolled growth. This is partly mediated by the Warburg effect, whereby glucose is converted into ATP and a subset of these anabolic substrates. Concurrently, mitochondrial mass and ATP production decline in most tumors. This raises the question of how increased supplies of glycolysis-derived anabolic substrates can be balanced with those generated by the TCA cycle. Using primary murine liver cancers and cell lines, we show that this can be explained by the dissociation of mitochondrial Complex V (CV or ATP synthase) into its component and functionally-independent Fo and F1 domains. This occurs as a result of marked reductions in MT-ATP6, a CV subunit that stabilizes the Fo-F1 association. Serving as a proton pore, Fo maintains a normal mitochondrial membrane potential without generating ATP, thus allowing the TCA cycle, electron transport chain and anaplerotic reactions to function at high levels. Concurrently, free F1 functions as an ATPase to prevent excessive ATP accumulation. The uncoupling of TCA cycle-derived anabolic substrate production from membrane hyperpolarization and ATP synthesis by a smaller population of more efficient mitochondria allows TCA cycle-generated anabolic precursors to match those generated via glycolysis.

cancer biology↗

bioRxiv2025

Adropin protects against cardiac metabolic remodeling and dysfunction in HFpEF

Cardiometabolic heart failure with preserved ejection fraction (HFpEF) is a heterogenous metabolic disease, which in the heart presents as left ventricle diastolic dysfunction, ventricular stiffness, and myocardial structural remodeling. Deleterious changes in cardiac metabolism are central to HFpEF pathophysiology, and proposed treatments for the disease have focused on repairing these defects. In this study, we used a preclinical mouse model that recapitulates cardiometabolic HFpEF to elucidate the molecular mechanisms driving cardiac dysfunction, and tested whether recombinant Adropin (a liver- and brain-derived endogenous peptide hormone) could reverse observed defects. We show that long-term treatment with Adropin reversed multiple markers of HFpEF-related cardiac dysfunction (including fibrosis, diastolic dysfunction, and cardiomyocyte hypertrophy). Using untargeted metabolomics, we found that Adropin treatment reduced hexosamine biosynthesis pathway activity, leading to a reduction in the O-GlcNAcylation of the cardiac fatty acid oxidation enzyme long chain acyl-CoA dehydrogenase (LCAD). Reducing LCAD O-GlcNAcylation increased LCAD activity in vitro, and reduced the accumulation of long-chain acylcarnitines in HFpEF mouse hearts in vivo. Our results suggest that Adropin may restore cardiac metabolic function in HFpEF, and that targeting this pathway may be a novel therapeutic avenue for this disease. CLINICAL PERSPECTIVE- Adropin is a circulating liver- and brain-derived peptide that regulates energy metabolism in the heart and other high metabolic-demand tissues. The plasma abundance of Adropin is decreased in diabetic, hypertensive, and aged individuals; all comorbid risk factors for the development of heart failure with preserved ejection (HFpEF). We therefore examined the potential role of Adropin in HFpEF pathophysiology. - Patients with HFpEF display significant reductions in circulating Adropin levels, matching those seen in comorbid diseases. In a mouse model of HFpEF, treatment with recombinant Adropin reduced diastolic dysfunction, cardiac fibrosis, and cardiomyocyte hypertrophy. - These data suggest that targeting the Adropin pathway may represent a new therapeutic approach in HFpEF.

physiology↗

bioRxiv2025

Soma to neuron communication links stress adaptation to stress avoidance behavior

In multicellular organisms, signaling from the nervous system to the peripheral tissues can activate physiological responses to stress. Here, we show that inter-tissue stress communication can also function in reverse, i.e. from the peripheral tissue to the nervous system. osm-8 mutants, which activate the physiological osmotic stress response in the C. elegans skin, also exhibit defective osmotic avoidance (Osm) behavior, via a direct and specific effect on ASH osmosensory neuron excitability. Both osm-8 and the Patched-related gene ptr-23, mutations in which suppress all osm-8 phenotypes, function in the hypodermal lysosomes to regulate both physiology and behavior. Unbiased lipidomics shows that osm-8 leads to a ptr-23-dependent elevation of the lysosome specific lipid bis(monoacylglycero)phosphate (BMP) and expansion of the pool of hypodermal lysosomes. Just as genetic activation of the osmotic stress response by loss of osm-8 in the hypodermis causes an Osm phenotype, acute physiological exposure to osmotic stress also confers a reversible Osm phenotype. Behavioral and genetic plasticity requires biosynthesis of the compatible solute glycerol, a key physiological output of the organismal osmotic stress response. However, ptr-23 is only required for osm-8 induced behavioral plasticity and not physiological plasticity. Instead, both genetic and physiologically induced Osm phenotypes require the unusual non-neuronal lysosomal V-ATPase subunit vha-5, which is also critical for organismal osmotic stress survival. Together, these data reveal that genetic or physiological activation of stress signaling from the skin elicits lysosome-associated signals that modulate organismal neurophysiology to attenuate a sensory neuron circuit. Such body-brain interoceptive communication may allow organisms to better match neuronal decision-making with organismal physiological state.

physiology↗

bioRxiv2025

Cardiac-specific deletion of GCN5L1 promotes fatty liver disease in HFpEF

The prevalence of cardiometabolic heart failure with preserved ejection fraction (HFpEF) continues to grow, representing over half of heart failure cases in the United States. As no specific medication for HFpEF exists, treatment guidelines focus on the management of comorbidities related to metabolic syndrome (e.g. obesity, diabetes, hypertension) that promote the disease1. These same comorbidities also drive pathology in non-cardiac tissues, and the links between cardiometabolic disease presentations in different organs are increasingly being recognized. Preclinical studies on the potential crosstalk between HFpEF and metabolic disease in the liver (e.g. metabolic dysfunction-associated liver disease; MASLD) have focused on how liver dysfunction may affect the heart, particularly through the release of secreted liver proteins. This may reflect the situation in the clinic, where incident MASLD is a risk factor for future HFpEF development. Here, in contrast to this developing paradigm of liver-initiated cardiac disease, we report for the first time a defect in cardiac metabolism related to the mitochondrial metabolic protein GCN5L1 that drives hepatic steatosis and MASLD in HFpEF.

physiology↗

bioRxiv2024

Lipoxin A4 yields an electrophilic 15-oxo metabolite that mediates FPR2 receptor-independent anti-inflammatory signaling

The enzymatic oxidation of arachidonic acid is proposed to yield trihydroxytetraene species (termed lipoxins) that resolve inflammation via ligand activation of the formyl peptide receptor, FPR2. While cell and murine models activate signaling responses to synthetic lipoxins, primarily 5S,6R,15S-trihydroxy-7E,9E,11Z,13E-eicosatetraenoic acid (lipoxin A4, LXA4), there are expanding concerns about the biological formation, detection and signaling mechanisms ascribed to LXA4 and related di- and tri-hydroxy {omega}-6 and {omega}-3 fatty acids. Herein, the generation and actions of LXA4 and its primary 15-oxo metabolite were assessed in control, LPS-activated and arachidonic acid supplemented RAW 264.7 macrophages. Despite protein expression of all enzymes required for LXA4 synthesis, both LXA4 and its 15-oxo-LXA4 metabolite were undetectable. Moreover, synthetic LXA4 and the membrane permeable 15-oxo-LXA4 methyl ester that is rapidly de-esterified to 15-oxo-LXA4, displayed no ligand activity for the putative LXA4 receptor FPR2, as opposed to the FPR2 ligand WKYMVm. Alternatively, 15-oxo-LXA4, an electrophilic ,{beta}-unsaturated ketone, alkylates nucleophilic amino acids such as cysteine to modulate redox-sensitive transcriptional regulatory protein and enzyme function. 15-oxo-LXA4 activated nuclear factor (erythroid related factor 2)-like 2 (Nrf2)-regulated gene expression of anti-inflammatory and repair genes and inhibited nuclear factor (NF)-{kappa}B-regulated pro-inflammatory mediator expression. LXA4 did not impact these macrophage anti-inflammatory and repair responses. In summary, these data show an absence of macrophage LXA4 formation and receptor-mediated signaling actions. Rather, if LXA4 were present in sufficient concentrations, this, and other more abundant mono- and poly-hydroxylated unsaturated fatty acids can be readily oxidized to electrophilic ,{beta}-unsaturated ketone products that modulate the redox-sensitive cysteine proteome via G-protein coupled receptor-independent mechanisms.

biochemistry↗

bioRxiv2023

Alternate splice variants of the mitochondrial fission protein DNM1L/Drp1 regulate mitochondrial dynamics and cell fate in ovarian cancer.

Aberrant mitochondrial fission/fusion dynamics have been reported in cancer cells. While post translational modifications are known regulators of the mitochondrial fission/fusion machinery, we show that alternative splice variants of the fission protein Drp1 (DNM1L) have specific and unique roles in cancer, adding to the complexity of mitochondrial fission/fusion regulation in tumor cells. Ovarian cancer specimens express an alternative splice transcript variant of Drp1 lacking exon 16 of the variable domain, and high expression of this splice variant relative to other transcripts is associated with poor patient outcome. Unlike the full-length variant, expression of Drp1 lacking exon 16 leads to decreased association of Drp1 to mitochondrial fission sites, more fused mitochondrial networks, enhanced respiration, and TCA cycle metabolites, and is associated with a more metastatic phenotype in vitro and in vivo. These pro-tumorigenic effects can also be inhibited by specific siRNA-mediated inhibition of the endogenously expressed transcript lacking exon 16. Moreover, lack of exon 16 abrogates mitochondrial fission in response to pro-apoptotic stimuli and leads to decreased sensitivity to chemotherapeutics. These data emphasize the significance of the pathophysiological consequences of Drp1 alternative splicing and divergent functions of Drp1 splice variants, and strongly warrant consideration of Drp1 splicing in future studies.

cancer biology↗

bioRxiv2022

The magnitude of sex differences in host-microbe interactions are time-of-day dependent

Circadian rhythms dynamically regulate sex differences in metabolism and immunity, and circadian disruption increases the risk of metabolic disorders. We investigated the role of sex-specific microbial circadian rhythms in host metabolism using germ-free and conventionalized female and male mice, dietary manipulations, coupled with a systems biology approach. Sex differences in circadian rhythms of genes involved in immunity and metabolism are dependent on oscillations in the microbiota, microbial metabolic functions, and microbial metabolites. Further, dietary factors modify the magnitude of sex differences in host-microbe circadian dynamics. We show that consuming an obesogenic high-fat, low-fiber diet produced sex-specific changes in circadian rhythms in microbiota, metabolites, and host gene expression, which were linked to sex differences in the severity of metabolic dysfunction. These results reveal that microbial circadian rhythms contribute to sex differences in metabolism, emphasizing the need to consider sex as a biological variable in research on microbial contributions to metabolic dysfunction. HIGHLIGHTSO_LIMicrobial circadian rhythms differ by sex. C_LIO_LISex-specific rhythms in host transcriptional networks are microbiome-dependent. C_LIO_LIDiet-induced obesity entrains new sex-specific rhythms in microbiome and host genes. C_LIO_LITiming of data collection influences magnitude of sex differences. C_LI

systems biology↗