Aquatic animals are increasingly challenged by O₂ fluctuations as a result of global warming, as well as eutrophication processes. Teleost fish show important species-specific adaptability to O₂ deprivation, moving from intolerance to a full tolerance of hypoxia and even anoxia. An example is provided by members of Cyprinidae which includes species that are amongst the most tolerant hypoxia/anoxia teleosts. Living at low water O₂ requires the mandatory preservation of the cardiac function to support the metabolic and hemodynamic requirements of organ and tissues which sustain whole organism performance. A number of orchestrated events, from metabolism to behavior, converge to shape the heart response to the restricted availability of the gas, also limiting the potential damages for cells and tissues. In cyprinids, the heart is extraordinarily able to activate peculiar strategies of functional preservation. Accordingly, by using these teleosts as models of tolerance to low O₂, we will synthesize and discuss literature data to describe the functional changes, and the major molecular events that allow the heart of these fish to sustain adaptability to O₂ deprivation. By crossing the boundaries of basic research and environmental physiology, this information may be of interest also in a translational perspective, and in the context of conservative physiology, in which the output of the research is applicable to environmental management and decision making.

Cardiac lipotoxicity is an important contributor to cardiovascular complications during obesity. Given the fundamental role of the endoplasmic reticulum (ER)-resident Selenoprotein T (SELENOT) for cardiomyocyte differentiation and protection and for the regulation of glucose metabolism, we took advantage of a small peptide (PSELT), derived from the SELENOT redox-active motif, to uncover the mechanisms through which PSELT could protect cardiomyocytes against lipotoxicity. To this aim, we modeled cardiac lipotoxicity by exposing H9c2 cardiomyocytes to palmitate (PA). The results showed that PSELT counteracted PA-induced cell death, lactate dehydrogenase release, and the accumulation of intracellular lipid droplets, while an inert form of the peptide (I-PSELT) lacking selenocysteine was not active against PA-induced cardiomyocyte death. Mechanistically, PSELT counteracted PA-induced cytosolic and mitochondrial oxidative stress and rescued SELENOT expression that was downregulated by PA through FAT/CD36 (cluster of differentiation 36/fatty acid translocase), the main transporter of fatty acids in the heart. Immunofluorescence analysis indicated that PSELT also relieved the PA-dependent increase in CD36 expression, while in SELENOT-deficient cardiomyocytes, PA exacerbated cell death, which was not mitigated by exogenous PSELT. On the other hand, PSELT improved mitochondrial respiration during PA treatment and regulated mitochondrial biogenesis and dynamics, preventing the PA-provoked decrease in PGC1-α and increase in DRP-1 and OPA-1. These findings were corroborated by transmission electron microscopy (TEM), revealing that PSELT improved the cardiomyocyte and mitochondrial ultrastructures and restored the ER network. Spectroscopic characterization indicated that PSELT significantly attenuated infrared spectral-related macromolecular changes (i.e., content of lipids, proteins, nucleic acids, and carbohydrates) and also prevented the decrease in membrane fluidity induced by PA. Our findings further delineate the biological significance of SELENOT in cardiomyocytes and indicate the potential of its mimetic PSELT as a protective agent for counteracting cardiac lipotoxicity.

Oxidative stress and endoplasmic reticulum stress (ERS) are strictly involved in myocardial ischemia/reperfusion (MI/R). Selenoprotein T (SELENOT), a vital thioredoxin-like selenoprotein, is crucial for ER homeostasis and cardiomyocyte differentiation and protection, likely acting as a redox-sensing protein during MI/R. Here, we designed a small peptide (PSELT), encompassing the redox site of SELENOT, and investigated whether its pre-conditioning cardioprotective effect resulted from modulating ERS during I/R. The Langendorff rat heart model was employed for hemodynamic analysis, while mechanistic studies were performed in perfused hearts and H9c2 cardiomyoblasts. PSELT improved the post-ischemic contractile recovery, reducing infarct size and LDH release with and without the ERS inducer tunicamycin (TM). Mechanistically, I/R and TM upregulated SELENOT expression, which was further enhanced by PSELT. PSELT also prevented the expression of the ERS markers CHOP and ATF6, reduced cardiac lipid peroxidation and protein oxidation, and increased SOD and catalase activities. An inert PSELT (I-PSELT) lacking selenocysteine was ineffective. In H9c2 cells, H₂O₂ decreased cell viability and SELENOT expression, while PSELT rescued protein levels protecting against cell death. In SELENOT-deficient H9c2 cells, H₂O₂ exacerbated cell death, that was partially mitigated by PSELT. Microscopy analysis revealed that a fluorescent form of PSELT was internalized into cardiomyocytes with a perinuclear distribution. Conclusions: The cell-permeable PSELT is able to induce pharmacological preconditioning cardioprotection by mitigating ERS and oxidative stress, and by regulating endogenous SELENOT.

The extraordinary capacity of the goldfish (Carassius auratus) to increase its cardiac performance under acute hypoxia is crucial in ensuring adequate oxygen supply to tissues and organs. However, the underlying physiological mechanisms are not yet completely elucidated. By employing an ex vivo working heart preparation, we observed that the time-dependent enhancement of contractility, distinctive of the hypoxic goldfish heart, is abolished by the Nitric Oxide Synthase (NOS) antagonist L-NMMA, the Nitric Oxide (NO) scavenger PTIO, as well as by the PI3-kinase (PI3-K) and sarco/endoplasmic reticulum Ca²⁺-ATPase 2a (SERCA2a) pumps’ inhibition by Wortmannin and Thapsigargin, respectively. In goldfish hearts exposed to hypoxia, an ELISA test revealed no changes in cGMP levels, while Western Blotting analysis showed an enhanced expression of the phosphorylated protein kinase B (pAkt) and of the NADPH oxidase catalytic subunit Nox2 (gp91phox). A significant decrease of protein S-nitrosylation was observed by Biotin Switch assay in hypoxic hearts. Results suggest a role for a PI3-K/Akt-mediated activation of the NOS-dependent NO production, and SERCA2a pumps in the mechanisms conferring benefits to the goldfish heart under hypoxia. They also propose protein denitrosylation, and the possibility of nitration, as parallel intracellular events.

Cardiovascular diseases (CVDs) remain the leading cause of morbidity and mortality worldwide, with increasing evidence suggesting that their origins may lie in prenatal life. Endocrine-disrupting chemicals (EDCs), such as bisphenol A (BPA), have been implicated in the alteration of fetal programming mechanisms that cause a predisposition to long-term cardiovascular vulnerability. However, the impact of prenatal endocrine disruption on fetal heart development and its sex-specific nature remains incompletely understood. This study investigates the molecular and structural effects of low-dose prenatal BPA exposure on fetal rat hearts. Our results reveal that BPA disrupts estrogen receptor (ER) signaling in a sex-dependent manner, with distinct alterations in ERα, ERβ, and GPER expression. BPA exposure also triggers significant inflammation, oxidative stress, and ferroptosis; this is evidenced by elevated NF-κB, IL-1β, TNF-α, and NLRP3 inflammasome activation, as well as impaired antioxidant defenses (SOD1, SOD2, CAT, and SELENOT), increased lipid peroxidation (MDA) and protein oxidation, decreased GPX4, and increased ACSL4 levels. These alterations are accompanied by increased markers of cardiac distension (ANP, BNP), extracellular matrix remodeling mediators, and pro-fibrotic regulators (Col1A1, Col3A1, TGF-β, and CTGF), with a more pronounced response in males. Histological analyses corroborated these molecular findings, revealing structural alterations as well as glycogen depletion in male fetal hearts, consistent with altered cardiac morphogenesis and metabolic stress. These effects were milder in females, reinforcing the notion of sex-specific vulnerability. Moreover, prenatal BPA exposure affected myocardial fiber architecture and vascular remodeling in a sex-dependent manner, as evidenced by reduced expression of desmin alongside increased levels of CD34 and Ki67. Overall, our findings provide novel insights into the crucial role of prenatal endocrine disruption during fetal heart development and its contribution to the early origins of CVD, underscoring the urgent need for targeted preventive strategies and further research into the functional impact of BPA-induced alterations on postnatal cardiac function and long-term disease susceptibility.

Alamandine is a peptide of the Renin Angiotensin System (RAS), either generated from Angiotensin A via the Angiotensin Converting Enzyme 2 (ACE2), or directly from Ang-(1–7). In mammals, it elicits cardioprotection via Mas-related G-protein-coupled receptor D (MrgD), and the NOS/NO system. In teleost fish, RAS is known to modulate heart performance. However, no information is available on the presence of a cardioactive ACE2/Alamandine axis. To fill this gap, we used the cyprinid teleost Carassius auratus (goldfish) for in silico and in vitro analyses. Via the NCBI Blast P suite we found that in cyprinids ace2 is phylogenetically detectable in a subcluster of proteins including ace2-like isoforms, and is correlated with a hypoxia-dependent pathway. By real-time PCR, Western Blotting, and HPLC, ACE2 and Alamandine were identified in goldfish heart and plasma, respectively. Both increased after chronic exposure to low O₂ (2.6 mg O₂ L⁻¹). By using an ex-vivo working goldfish-heart preparation, we observed that in vitro administration of exogenous Alamandine dose-dependently stimulates myocardial contractility starting from 10⁻¹¹ M. The effect that involved Mas-related receptors and PKA occurred via the NOS/NO system. This was shown by exposing the perfused heart to the NOS inhibitor L-NMMA (10⁻⁵ M) that abolished the cardiac effect of Alamandine and was supported by the increased expression of the phosphorylated NOS enzyme in the extract from goldfish heart exposed to 10⁻¹⁰ M Alamandine. Our data are the first to show that an ACE2/Alamandine axis is present in the goldfish C. auratus and, to elicit cardiac modulation, requires the obligatory involvement of the NOS/NO system.