Revealing the biochemical regulations of L-PGDS in hepatic insulin-resistance using HepG2 cells

Metabolic dysfunction-associated steatotic liver disease (MASLD) is the most common chronic liver disease, and its prevalence poses a serious health threat globally. MASLD is a multifactorial hepatic disorder, but insulin resistance is a key player. Our prior in vivo studies revealed that the absence of lipocalin prostaglandin D₂ synthase (L-PGDS) leads to the development of MASLD, often coexisting with insulin resistance. Briefly, L-PGDS belongs to the arachidonic acid pathway and enzymatically catalyzes the conversion of prostaglandin H₂ to prostaglandin D_2, which imparts physiological effects via DP1 and DP2 receptors. L-PGDS plays a crucial role in MASLD; however, its mechanistic regulation remains unexplored. Therefore, we aimed to study the biochemical regulation of L-PGDS using a cellular model of MASLD. We successfully recapitulated the MASLD phenotype in HepG2 cells by co-treating with palmitate and insulin. Our results showed significant downregulation of L-PGDS and decreased PGD₂ levels in an insulin-resistant state. To study this L-PGDS downregulation, we employed MG132, chloroquine, cycloheximide, and immunoprecipitation to assess proteasomal degradation, autophagy, translational activity, and ubiquitination, respectively. However, the above pathways were not involved. Interestingly, gene and protein expression results revealed the clues for L-PGDS downregulation, showing significantly decreased transcription and subsequently protein levels. Additionally, subcellular localization results showed that insulin resistance induced the trafficking of L-PGDS from the cytoplasm to the nucleus. In summary, L-PGDS downregulation possibly involves transcription-translation and/or subcellular localization pathways. However, further studies are required to delineate the molecular mechanism of L-PGDS downregulation and apply this knowledge to MASLD pathogenesis and treatment.