2025 Theses Doctoral

Hepatic Stellate Cell and Nonparenchymal LTBP3/TGFβ Contributes to Hepatic Triglyceride Content

Mayfield, Brent Charles

As obesity plagues the United States and the globe on a larger scale every year, finding treatments to manage its metabolic complications, including metabolic dysfunction-associated steatotic liver disease (MASLD), become more critical. When MASLD transitions to metabolic associated steatohepatitis (MASH) and fibrosis, the damage may be irreversible. MASH has no approved pharmacotherapy, leaving a large unmet need. This therapeutic vacuum is related to an incomplete understanding of molecular mediators, exacerbated by diverse cell populations that worsen disease progression from liver inflammation that defines MASH and builds up to cirrhosis.

Our research focuses on understanding the role of hepatocytes in MASH. Through extensive RNA sequencing analyses, we identified latent TGFβ binding protein-3 (Ltbp3)—a key regulator of MASH and a crucial mediator of TGFβ secretion—as a novel player in the disease. We hypothesized that LTBP3 was, at least in part, a driver of hepatocyte induced fibrosis through a novel hepatocyte to hepatic stellate cell (HSC) communication axis. Using GalNAc tools, previously considered hepatocyte-specific, we reduced Ltbp3 expression in multiple diet-induced MASH models. Instead of a decrease in fibrosis, this led to a significant decrease in hepatic triglyceride levels.

Additionally, global suppression of hepatocyte TGFβ activity mirrored the effects of GalNAc tools, revealing that triglyceride regulation is linked to changes in de novo lipogenesis (DNL). We identified no change in VLDL-TG secretion, intestinal and systemic absorption of dietary triglyceride, or fatty acid oxidation. As we have not seen gene expression changes typical of DNL, we hypothesize that hepatocyte TGFβ activity may induce DNL in an atypical way. In future, we plan on performing RNA Sequencing in the hepatocyte TGFβ activity ablation Smad4 knockout mice to examine if any atypical lipogenesis genes may be affected. We are also studying hepatocyte TGFβ activity’s effect on typical DNL protein stability.

As the hepatocyte specific Ltbp3 knockout mouse does not recapitulate the loss in hepatic TG, further investigation revealed that at the administered dose, our GalNAc tools were targeting multiple liver cell types beyond hepatocytes. We discovered that non-parenchymal cell (NPC) derived Ltbp3 is primarily responsible for the observed phenotype. These findings suggest a previously unrecognized mechanism of NPC-hepatocyte communication, particularly involving hepatic stellate cells. Collectively, we propose that hepatic stellate cell and other NPC Ltbp3 is responsible for the secretion of TGFβ. This TGFβ is responsible for increases in the rate of DNL in the hepatocyte, producing more hepatic triglycerides and advances the disease.