Increased Lactate Can Promote Histone Lactylation in Failing Right Ventricular Cardiomyocytes in Pulmonary Arterial Hypertension

Abstract Background: Using a multimodal approach, we recently showed that, in pulmonary arterial hypertension (PAH), lactate is a key feature of altered cardiomyocyte metabolism in the failing right ventricle (RV) that is detectable in human plasma. Increased lactate production has been shown to stimulate histone lactylation thus linking dysregulated cellular metabolism with epigenetic modification. We hypothesized that elevated lactate in the failing RV cardiomyocytes can promote epigenetic modification in an autocrine and paracrine fashion. Methods: Immunoblotting was performed on frozen RV tissue from control (n=3), and PAH (n=9) patients with RV failure (autopsy tissue), and BMPR2-mutant mice (murine model of PAH with universal expression of BMPR2 mutation, n=4) and control mice (n=4), and immunofluorescence studies were conducted on paraffin-embedded human RV tissue from control (n=5), IPAH (n=5), and HPAH (n=5) patients, using L-lactyllysine, MCT1, and MCT4 antibodies. Mass spectrometric analysis was done to determine lactate concentration in organs and plasma from BMPR2-mutant (n=4) and control mice (n=4). Results: In human PAH-RVs, we examined the autocrine effect of increased lactate on histone lysine lactylation (a novel protein posttranslational modification driven by lactate). We observed a significant increase in lactyllysine in both human PAH-RVs and BMPR2-mutant mouse RVs (p<0.05) compared to controls. Human PAH-RV cardiomyocytes also showed significant immunolocalization of lactyllysine in the cytoplasm (p<0.05) compared to controls. To study the paracrine effects of lactate, we examined the efflux of lactate via lactate-transporter proteins MCT1 and MCT4 in human PAH-RVs vs controls. Human PAH-RVs demonstrated an increase in MCT-4 expression (p<0.05) and a trend towards an increase in MCT-1 expression compared to controls. MCT-1 localization in the cytoplasm was significantly increased in all PAH-RV cardiomyocytes (p<0.05), while MCT-4 was notably elevated in idiopathic PAH cardiomyocytes (p<0.05). Finally, to discern which tissues contribute to the elevated plasma lactate concentration (as shown in our published finding), we measured lactate levels in various organs of BMPR2-mutant and control mice by mass spectrometry. In BMPR2-mutant mice vs. controls, lactate was significantly increased in the RV, lung, and plasma (p<0.01) but not spleen, kidney, liver gastrocnemius muscle, and LV. Conclusion: In the human PAH-RV, lactate can promote epigenetic modification in an autocrine fashion, manifesting as histone lactylation in the cytoplasm. Elevated plasma lactate likely originates specifically in key PAH-related organs (lung and RV), potentially causing both local and systemic adverse effects. Altered cardiomyocyte metabolism resulting in elevated lactate production may have significant implications for RV dysfunction in PAH.