Background: Sphingosine-1-phosphate (S1P) is a bioactive sphingolipid that regulates vascular tone, inflammation, and central aspects of cardiac function, including cardiomyocyte survival and contractility. It is generated by two kinases, SphK1 and SphK2, which differ in subcellular localization and function. While SphK1 is well established as a modulator of vascular barrier integrity and cardioprotection, the role of SphK2 in cardiac physiology remains insufficiently understood. SphK2-derived S1P has been implicated in mitochondrial function and cardiomyocyte survival, suggesting a critical role in maintaining myocardial homeostasis. We investigated whether SphK2 deficiency affects cardiac structure and function in response to chronic Angiotensin II-induced stress.
Methods: Male SphK2-/- and wild-type (WT) littermate controls were infused with Angiotensin II (Ang II; 1000 ng/kg/min) for 28 days using subcutaneously implanted osmotic minipumps. Cardiac function was evaluated by echocardiography at baseline and 14 days after pump implantation. Molecular markers of heart failure, including B-type natriuretic peptide (BNP), atrial natriuretic peptide (ANP), and β-myosin heavy chain (Myh7), were quantified by qPCR from cardiac tissue, while NT-proBNP levels were determined in plasma by ELISA. Myocardial fibrosis was analysed histologically by Sirius Red staining and quantified as the ratio of fibrotic to total myocardial area. Targeted sphingolipidomic profiling was performed to assess alterations in cardiac and plasma sphingolipid composition. In addition, myofilament calcium sensitivity and passive tension were determined in isolated permeabilized cardiomyocytes to evaluate sarcomeric function and stiffness.
Results: SphK2-/- mice displayed a significantly higher mortality rate under Ang II infusion compared with WT controls (42% vs. 14%, p = 0.048). Echocardiography revealed a marked reduction in ejection fraction (WT: 41.02; SphK2-/-: 31.25%; p <0.0001), accompanied by increased ESV (41.19 vs. 50.71 µl, p = 0.0108). At the molecular level, cardiac mRNA expression of ANP, BNP, Myh-7 was strongly upregulated, while NT-proBNP was increased in the plasma as compared to littermate controls. Sirius Red staining demonstrated enhanced collagen deposition (4.66% vs. 7.8%; p < 0.0213), paralleled by elevated expression of fibrotic markers including Col1a1, Col3a1, and α-SMA. Sphingolipidomic profiling of hearts revealed elevated cardiac ceramide (Cer16:0; Cer18:0) levels under Ang II, with substantially higher increase in SphK2-/- mice. Isolated cardiomyocytes from SphK2-/- hearts displayed increased passive tension, reflecting higher stiffness and impaired mechanical relaxation.
Conclusion: SphK2 deficiency markedly exacerbates Ang II-induced cardiac dysfunction, fibrosis, and maladaptive remodelling. The loss of SphK2 appears to compromise cardiomyocyte structural integrity with adverse effects on tension. The exact mechanisms are under investigation. These findings identify SphK2 as an important regulator of cardiac stress responses and a potential therapeutic target to preserve cardiac function during chronic pressure overload.
