The role of sphingolipids in multi-organ lipotoxicity in metabolic syndrome.

The global incidence of metabolic dysfunction–associated steatohepatitis (MASH) and heart failure with preserved ejection fraction (HFpEF) is rising due to the increasing prevalence of metabolic syndrome (MetS). Both MASH and HFpEF share comorbidities such as obesity, type 2 diabetes, and hypertension, which suggest common pathophysiological mechanisms. These diseases are characterized by lipotoxicity and mitochondrial dysfunction. Current treatments for MetS, MASH, and HFpEF are limited and often target specific organs, increasing the risk of drug interactions and side effects. This study examines the role of sphingolipids, particularly ceramides, in multi-organ lipotoxicity within MetS. Preliminary data and current literature indicate that ceramides play a crucial role in metabolic diseases. By modeling biosynthetic pathways for ceramide, we aimed to identify new intracellular targets to modulate ceramide content. Given the lower SPTLC1 levels (key enzyme in ceramide de novo synthesis) in HFpEF hearts, reducing ceramide content using SPTLC1 inhibitor like myriocin, presents a challenge. Alternatively, adiponectin receptors have emerged as potential therapeutic targets, acting after ceramide synthesis. JT003, an AdipoR1/2 dual agonist, has proven its effectiveness improving lipid metabolism, reducing fibrosis and inflammation via AMPK and PPARα signaling pathways. Whether JT003 impact on ceramide metabolism has never been previously explored. In this study, we first investigated ceramide metabolism and triglyceride accumulation in the hearts of C57BL-6J-mice on standard (STD) or high-fat diets (HFD), with or without myriocin treatment. We used Oil Red O staining and immunofluorescence to quantify triglycerides and ceramides, respectively. Our results showed that HFD significantly increased both triglycerides and ceramides levels in WT mice, which were both reduced by myriocin treatment, further emphasizing the role of ceramide metabolism in the heart. Secondly, in in vitro experiments, we modeled ceramide accumulation using palmitate treatment on various cell lines, including 3T3-L1, HEK293, AC16, and HepG2 cells. JT003 treatment significantly reduced ceramide content across all cell lines by enhancing ceramide degradation through ceramidase activity without altering the transcription of de novo synthesis enzymes. Our findings suggest that JT003 could be a promising therapeutic compound for targeting ceramide accumulation in MetS, MASH, and HFpEF, providing a comprehensive treatment strategy for these complex and interconnected conditions.