Biology subjects

Vazquez-Medina, J. P.

Publications and source records attributed to Vazquez-Medina, J. P..

12 recordsLinked to original sources

bioRxiv2026

Iron export and lipid droplets shield deep-diving elephant seal cells from lipid peroxidation

Elephant seals are remarkable breath-hold divers, capable of remaining submerged for up to two hours during diving bouts. These dives entail repeated, extreme hypoxia/reoxygenation events that would induce severe lipid peroxidation and tissue dysfunction in most mammals. Here, we show that primary vascular endothelial cells derived from elephant seals possess an intrinsic resistance to lipid peroxidation. Comparative transcriptomic and lipidomic profiling across seal, human, and sheep cells identified ferroptosis - an iron-dependent, lipid peroxidation-driven cell death pathway - as uniquely regulated in seal cells following hydroperoxide exposure. Mechanistically, seal cells exhibit robust baseline expression of acyl-CoA synthetase long-chain family member 3 (ACSL3), alongside rapid, seal-specific induction of the sole mammalian iron exporter, ferroportin (SLC40A1). Functional validation using genetic and pharmacological approaches revealed that seal cells are naturally enriched in monounsaturated fatty acids and triglycerides and utilize lipid droplet biogenesis and active iron export as dual protective axes to evade lipid peroxidation. Together, these findings show that elephant seal cells employ a coordinated cytoprotective network of lipid remodeling and iron handling to withstand the severe challenges of deep diving. SIGNIFICANCE STATEMENTDeep-diving marine mammals repeatedly experience extreme hypoxia-reoxygenation events that would induce severe oxidative damage in most terrestrial mammals. However, vascular cells derived from seals naturally resist lipid peroxidation, a major driver of ischemia-reperfusion injury. Here, we show that elephant seal endothelial cells evade lipid peroxidation through two complementary mechanisms: lipid droplets that sequester peroxidation-prone phospholipids, and rapid iron export that limits lipid peroxide formation. These findings reveal naturally evolved cellular strategies that protect against vascular oxidative stress, offering new insights into physiological resilience against ischemia-reperfusion injury.

physiology↗

bioRxiv2026

Phthalate exposure induces inflammatory signaling and alters mitochondrial respiration in marine mammal and human cells

This study investigated the transcriptional and bioenergetic responses to monoethylhexyl phthalate (MEHP) in primary fibroblasts derived from northern elephant seals (Mirounga angustirostris), common dolphins (Delphinus delphis), and humans, using RNA-seq, extracellular flux assays, and high-resolution microscopy of the mitochondrial reticulum. MEHP exposure did not induce cytotoxicity but triggered species-specific changes in gene expression and mitochondrial metabolism and morphology. Human cells showed the greatest transcriptional response, upregulating genes involved in detoxification, antioxidant, and inflammation while downregulating lipid metabolism pathways. The highest dose also decreased mitochondrial respiration and increased mitochondrial fragmentation, triggering a metabolic shift toward glycolysis. Elephant seal cells showed delayed glycolytic shifts, maintaining mitochondrial respiration and upregulating antioxidant, immune, and metabolic pathway genes through the highest dose. Despite mitochondrial fragmentation, they upregulated mitochondrial fusion/fission and trafficking genes. Dolphin cells exhibited the fewest changes in gene expression, mostly in hormone signaling and mitotic pathways. They showed dose-dependent declines in both respiration and glycolytic rates, even at the lowest concentration, yet maintained mitochondrial structural integrity while upregulating stress- and hypoxia-induced genes. These distinct strategies highlight species-specific susceptibility to toxicant-induced stress, offering new insights into how marine mammals respond to plastic-derived contaminants and reinforcing the need for species-specific ecotoxicological risk assessments.

physiology↗

bioRxiv2026

Molecular signatures and cellular responses underlying hypoxic adaptation in sea turtles

Hypoxia-inducible factors (HIFs) are transcriptional regulators that orchestrate the canonical response to low-oxygen tension in animal cells. Vertebrates possess three HIF- isoforms, which arose from two gene duplication events of the ancestral HIF-1 gene. Here, we examined whether the HIF gene family (HIF-1, HIF-2, HIF-3, and HIF-1N inhibitor) shows evidence of positive selection in hypoxia-tolerant reptiles (Testudines), compared evolutionary patterns within the family, and assessed the transcriptional response to hypoxia in primary cells derived from a hypoxia-tolerant (Caretta caretta) and a non-tolerant (Sceloporus occidentalis) reptile. We found that HIF-1, HIF-2, and HIF-1N are highly conserved across reptiles, whereas HIF-3 is under positive selection in Testudines. We also identified multiple novel regulatory motifs unique to Testudines. Transcriptional signatures of hypoxia exposure indicated stark differences between lizards and turtles. Whereas lizard cells exhibited a canonical response to hypoxia, characterized by enriched cell-survival pathways, sea turtle cells exhibit a robust, distinctive transcriptional response involving enriched pathways related to protein synthesis, quality maintenance, and mitochondrial integrity. Surprisingly, cis-regulatory element analysis did not show HIFs as key regulators of the transcriptional response in either species. Instead, TFDP1 in lizard cells and E2F1 in sea turtle cells emerged as potential key regulators. TFDP1 regulates the cell cycle, specifically DNA synthesis and cell cycle progression, while E2F regulates DNA-damage response, apoptosis, metabolism, and fatty acid biosynthesis. These results suggest that the reptilian response to hypoxia is shaped by transcriptional plasticity, while highlighting key regulatory mechanisms driving hypoxic adaptation in sea turtle cells. However, positive selection of HIF-3 and novel HIF motifs suggest a combined, but yet to be uncovered, contribution of regulatory and coding sequence evolutionary mechanisms shaping hypoxia tolerance in Testudines.

molecular biology↗

bioRxiv2025

Prolonged fasting and glucocorticoid exposure drive dynamic DNA methylation in elephant seals

Elephant seals experience prolonged fasting while breeding, molting, and undergoing postnatal development. Fasting elephant seals adjust neuroendocrine function and gene expression to cope with potentially detrimental effects associated with extended fasting. DNA methylation alters gene expression by modulating accessibility to regions necessary to initiate transcription. The role of fasting and glucocorticoids on DNA methylation in elephant seals is understudied. We evaluated whether fasting alters global blood DNA methylation, the potential correlation between increased glucocorticoids and methylation, and the effects of glucocorticoids on DNA methylation in seal muscle cells in primary culture. We found that fasting transiently increases blood DNA methylation and that blood DNA methylation levels correlate with plasma cortisol. Hence, we then conducted bioinformatic analyses to identify regions in the elephant seal glucocorticoid receptor (GR) promoter that influence gene transcription through methylation (CPG islands). We identified one CpG island within the putative promoter region of GR gene. Methylation in this region, however, was unaffected by prolonged fasting. We then investigated whether exogenous glucocorticoids alter DNA methylation and gene expression profiles in seal muscle cells in primary culture (myotubes). Exposure to glucocorticoids for 12 or 48 hours decreased DNA methylation while upregulating pro-survival gene expression in seal myotubes. Our results show that whereas prolonged fasting transiently increases DNA methylation in elephant seal blood, sustained exposure to exogenous glucocorticoids decreases DNA methylation and activates a pro-survival transcriptional program in seal myotubes. Therefore, our results suggest that DNA methylation is a plastic, potentially cell-type-specific response that regulates gene expression in fasting seals. Summary statementDNA methylation is a plastic response to fasting and increased glucocorticoids in elephant seals. Our work underscores the role of epigenetic regulation of gene expression during energetically challenging conditions in seals and potentially other mammals.

physiology↗

bioRxiv2025

Exogenous Thyroxine Increases Cardiac Nrf2-TRX in Insulin Resistant OLETF Rats

Cardiovascular disease (CVD) is the leading cause of death among individuals with Type II diabetes (T2D), affecting approximately 30 million people in the United States. During insulin resistance, the heart undergoes a metabolic shift, leading to increased reactive oxygen species (ROS) generation, lipotoxicity, and mitochondrial dysfunction, ultimately contributing to cardiovascular dysfunction. The effects of thyroid hormones (THs) on redox biology and oxidative stress remain inconclusive, necessitating further investigation. In this study, insulin-resistant Otsuka Long Evans Tokushima Fatty (OLETF) rats were used to assess the impact of exogenous thyroxine (exoT4) on NADPH oxidases (NOX) and antioxidant defenses in the heart. Rats were assigned to four groups: (1) lean control, Long Evans Tokushima Otsuka (LETO; n=6), (2) LETO + T4 (8 g/100g BM/day for 5 weeks; n=7), (3) untreated OLETF (n=6), and (4) OLETF + T4 (n=7). NOX4 mRNA expression was two-fold greater in OLETF rats compared to LETO. T4 treatment increased NOX4 protein abundance by 56% in OLETF. Additionally, T4 normalized lipid peroxidation (4-hydroxynonenal) and tumor necrosis factor- (TNF-) levels while increasing nuclear factor erythroid 2-related factor 2 (Nrf2) mRNA expression by 158% compared to LETO and enhancing nuclear Nrf2 protein expression by 45% compared to untreated OLETF. Thioredoxin (TRX) expression, suppressed in OLETF, was increased by 88% following T4 treatment. ExoT4 increased mitofusin 2 (Mfn2) protein abundance in OLETF by 49% compared to LETO. These findings suggest that thyroid hormone treatment may have cardioprotective effects mediated by Nrf2 in the heart during metabolic syndrome (MetS).

physiology↗

bioRxiv2024

Hypoxia exposure fine-tunes mitochondrial function in sea turtle cells

Sea turtles experience extreme fluctuations in oxygen availability derived from extended breath-hold diving, yet the cellular adjustments that underlie hypoxia tolerance in these animals remain poorly understood. Here, we used metabolite profiling, extracellular flux assays, and microscopic analyses of the mitochondrial reticulum to study how primary cells derived from sea turtles and lizards cope with extended hypoxia exposure. Cells from both species proliferate in primary culture, stain positive for fibroblast markers, are metabolically active, and stabilize HIF1- when exposed to chemical or environmental hypoxia. In contrast to lizard cells, sea turtle cells exhibit a faster and more robust response to 1 or 24-hour hypoxia exposure (0.1% O2), upregulating antioxidant pathways and optimizing oxygen use rather than relying on glycolytic metabolism. Similarly, the mitochondrial reticulum is maintained without apparent fragmentation during hypoxia exposure in sea turtle cells. Consistent with these observations, mitochondrial function readily recovers in sea turtle but not lizard cells upon reoxygenation. These findings show that sea turtle cells undergo intrinsic metabolic adjustments to cope with extreme oxygen fluctuations, aligning with the remarkable hypoxic tolerance exhibited by these animals, which can endure up to 7 hours of breath-holding underwater.

physiology↗

bioRxiv2024

Extensive longevity and DNA virus-driven adaptation in nearctic Myotis bats

Summary ParagraphThe genus Myotis is one of the largest clades of bats, and exhibits some of the most extreme variation in lifespans among mammals alongside unique adaptations to viral tolerance and immune defense1-3. To study the evolution of these phenotypes we generated cell lines and near-complete genome assemblies for eight closely related Myotis species. Using genome-wide screens of positive selection, analyses of structural variation, and functional experiments in primary cells, we identify patterns of adaptation contributing to longevity, cancer resistance, and viral interactions. We demonstrate distinct modes of adaptation to DNA and RNA viruses compared to all other mammals, with bats exhibiting genome-wide overrepresentation of positive selection for DNA virus-interacting proteins and elevated rates of copy number variation for RNA virus-interacting proteins. Characterization of Myotis-specific duplications of the key immune factor protein kinase R (PKR) reveals multiple ancient segregating trans-species copy number polymorphisms. We show that the recurrent evolution of longevity seen in Myotis is associated with positive selection in cancer pathways, and demonstrate a unique response to DNA damage in primary cells of the long-lived M. lucifugus. Together, our results suggest that bats remarkable longevity and immunity are linked through pleiotropic adaptations to viruses and aging-related disease.

genomics↗

bioRxiv2023

Hypoxia blunts angiogenic signaling and upregulates the antioxidant system in elephant seal endothelial cells

Elephant seals experience extreme hypoxemia during diving bouts. Similar depletions in oxygen availability characterize pathologies including myocardial infarction and ischemic stroke in humans, but seals manage these repeated episodes without injury. However, the real-time assessment of the molecular changes underlying protection against hypoxic injury in seals remains restricted by their at-sea inaccessibility. Hence, we developed a proliferative arterial endothelial cell culture system to assess the molecular response to prolonged hypoxia. Seal and human cells exposed to 1% O2 for up to 6 h demonstrated differential responses to both acute and prolonged hypoxia. Seal cells decouple stabilization of the hypoxia-sensitive transcriptional regulator HIF-1 from angiogenic signaling at both the transcriptional and cellular level. Rapid upregulation of genes involved in the glutathione (GSH) metabolism pathway supported maintenance of GSH pools and increases in intracellular succinate in seal but not human cells during hypoxia exposure. High maximal and spare respiratory capacity in seal cells after hypoxia exposure occurred in concert with increasing mitochondrial branch length and independent from major changes in extracellular acidification rate, suggesting seal cells recover oxidative metabolism without significant glycolytic dependency after hypoxia exposure. In sum, our studies show that in contrast to human cells, seal cells adapt to hypoxia exposure by dampening angiogenic signaling, increasing antioxidant protection, and maintaining mitochondrial morphological integrity and function.

physiology↗

bioRxiv2021

Oxidative stress is a potential cost of synchronous nesting in olive ridley sea turtles

Olive ridley sea turtles, Lepidochelys olivacea, exhibit a polymorphic reproductive behaviour nesting in solitary or in mass aggregations termed "arribadas", where thousands of turtles nest at once. Arribadas may provide fitness benefits including mate finding during nearshore aggregations and predator satiation at the time of hatching, but the potential costs of arribada nesting remain understudied. To explore the potential trade-offs of the fitness benefits associated with arribada nesting, we collected blood from olive ridley turtles nesting in arribada and solitary. We measured reproductive and metabolic hormones (progesterone, estradiol, testosterone, thyroxine, and triiodothyronine), triglycerides (TG), non-esterified fatty acids (NEFA) and markers of oxidative damage (4-hydroxynonenal, malondialdehyde, protein carbonyls, and nitrotyrosine). Arribada nesters were bigger and had higher levels of progesterone than solitary nesters. Similarly, thyroid hormones were higher in individuals nesting in arribada than in solitary nesters, while TG and NEFA were positively correlated in arribada but not in solitary nesters. Nesting in arribada was associated with increased lipid peroxidation and protein carbonyls compared to solitary nesting. These results suggest that nesting in arribada is potentially more energetically expensive than nesting solitarily, and that oxidative stress may be a trade-off of the fitness benefits associated with arribada nesting.

physiology↗

bioRxiv2021

Short-term elevations in glucocorticoids do not alter telomere lengths: A systematic review and meta-analysis of non-primate vertebrate studies

BackgroundThe neuroendocrine stress response allows vertebrates to cope with stressors via the activation of the Hypothalamic-Pituitary-Adrenal (HPA) axis, which ultimately results in the secretion of glucocorticoids (CORT). Glucocorticoids have pleiotropic effects on behavior and physiology, and might influence telomere length dynamics. During a stress event, CORT mobilizes energy towards survival mechanisms rather than to telomere maintenance. Additionally, reactive oxidative species produced in response to increased CORT levels can damage telomeres, also leading to telomere shortening. In our systematic review and meta-analysis, we tested whether CORT levels impact telomere length and if this relationship differs among time frame, life history stage, or stressor type. We hypothesized that elevated CORT levels are linked to a decrease in telomere length. MethodsTo test this hypothesis, we conducted a literature search for studies investigating the relationship between telomere length and CORT levels in non-human vertebrates using four search engines: Web of Science, Google Scholar, Pubmed and Scopus, last searched on September 27th, 2020. This review identified 31 studies examining the relationship between CORT and telomere length. We pooled the data using Fishers Z for 15 of these studies. All quantitative studies underwent a risk of bias assessment. This systematic review study was registered in the Open Science Framework Registry (https://osf.io/rqve6). ResultsThe pooled effect size from fifteen studies and 1066 study organisms shows no relationship between CORT and telomere length ((Fishers Z= 0.1042, 95% CI = 0.0235; 0.1836). While these results support some previous findings, other studies have found a direct relationship between CORT and telomere dynamics, suggesting underlying mechanisms or concepts that are not currently taken into account in our analysis. The risk of bias assessment revealed an overall low risk of bias with occasional instances of bias from missing outcome data or bias in the reported result. ConclusionWe highlight the need for more targeted experiments to understand how conditions, such as experimental timeframes, stressor(s), and stressor magnitudes can drive a relationship between the neuroendocrine stress response and telomere length.

physiology↗

bioRxiv2021

Repeated stimulation of the HPA axis alters white blood cell counts without increasing oxidative stress or inflammatory cytokines in fasting elephant seal pups

The hypothalamic-pituitary-adrenal (HPA) axis controls the release of glucocorticoids, which regulate immune and inflammatory function by modulating cytokines, white blood cells (WBCs), and oxidative stress via glucocorticoid receptor (GR) signaling. Although the response to HPA activation is well characterized in many species, little is known about the impacts of HPA activation during extreme physiological conditions in marine mammals. Hence, we challenged 18 simultaneously fasting and developing elephant seal pups with daily intramuscular injections of adrenocorticotropin (ACTH), a GR antagonist (RU486), or a combination (ACTH+RU486) for four days (4d). We collected blood at baseline, two hours (2h), and 4d after the beginning of treatment. ACTH and ACTH+RU486 elevated serum aldosterone and cortisol at 2h, with effects diminishing at 4d. RU486 alone induced a compensatory increase in aldosterone, but not cortisol, at 4d. ACTH decreased neutrophils at 2h while decreasing lymphocytes and increasing neutrophil:lymphocyte ratio at 4d. These effects were abolished by RU486. Despite alterations in WBCs, there was no effect of ACTH or RU486 on transforming growth factor-{beta} or interleukin-6 levels; however, both cytokines decreased with the 4-d fasting progression. Similarly, ACTH did not impact protein oxidation, lipid peroxidation, or antioxidant enzymes, but plasma isoprostanes and catalase activity decreased while glutathione peroxidase increased with fasting progression. These data demonstrate differential acute (2h) and chronic (4d) modulatory effects of HPA activation on WBCs and that the chronic effect is mediated, at least in part, by GR. These results also underscore elephant seals resistance to potential oxidative stress derived from repeated HPA activation. Summary statementMany species experience oxidative stress and inflammation after repeated activation of the hypothalamic-pituitary-adrenal axis. We show that simultaneously fasting and developing elephant seals are resistant to repeated hypothalamic-pituitary-adrenal axis activation.

physiology↗

bioRxiv2021

Elephant seal muscle cells adapt to sustained glucocorticoid exposure by shifting their metabolic phenotype

Elephant seals experience natural periods of prolonged food deprivation while breeding, molting, and undergoing postnatal development. Prolonged food deprivation in elephant seals increases circulating glucocorticoids without inducing muscle atrophy, but the cellular mechanisms that allow elephant seals to cope with such conditions remain elusive. We generated a cellular model and conducted transcriptomic, metabolic, and morphological analyses to study how seal cells adapt to sustained glucocorticoid exposure. Seal muscle progenitor cells differentiate into contractile myotubes with a distinctive morphology, gene expression profile, and metabolic phenotype. Exposure to dexamethasone at three ascending concentrations for 48h modulated the expression of 6 clusters of genes related to structural constituents of muscle and pathways associated with energy metabolism and cell survival. Knockdown of the glucocorticoid receptor (GR) and downstream expression analyses corroborated that GR mediates the observed effects. Dexamethasone also decreased cellular respiration, shifted the metabolic phenotype towards glycolysis, and induced mitochondrial fission and dissociation of mitochondria-ER interactions without decreasing cell viability. Knockdown of DDIT4, a GR target involved in the dissociation of mitochondria-ER membranes, recovered respiration and modulated antioxidant gene expression. These results show that adaptation to sustained glucocorticoid exposure in elephant seal myotubes involves a metabolic shift toward glycolysis, which is supported by alterations in mitochondrial morphology and a reduction in mitochondria-ER interactions, resulting in decreased respiration without compromising cell survival.

physiology↗