# Hepatocellular EVs Regulate Lipid Metabolism via SIRT1/SREBP−1c/PGC−1α Signaling in Primary Calf Hepatocytes

## TL;DR

This study shows that EVs from healthy calf liver cells can help reduce fat metabolism issues in sick calves by regulating specific signaling pathways.

## Contribution

The study demonstrates the role of hepatocellular EVs in modulating lipid metabolism via SIRT1/SREBP−1c/PGC−1α signaling in calf hepatocytes.

## Key findings

- NK-derived EVs inhibited SREBP−1c and increased SIRT1 and PGC−1α expression, improving lipid metabolism.
- CK-derived EVs worsened lipid metabolism in normal and NEFA-treated hepatocytes.
- SIRT1 overexpression confirmed the pathway's role in EV-mediated lipid regulation.

## Abstract

SIRT1-SREBP−1c/PGC−1α signaling is involved in the production of non-esterified fatty acids (NEFAs) and liver lipid metabolism disorders in ketotic calf. The molecules contained in extracellular vesicles (EVs) regulate intercellular communication, and research on calf hepatocytes−derived EVs has become a hot spot. We hypothesized that EVs in cell culture supernatants could affect lipid metabolism in hepatocyte models via SIRT1/SREBP−1c/PGC−1α signaling. Non-ketosis (NK, 0 mM NEFA) and clinical ketosis calf models (CK, 2.4 mM NEFAs) were established in vitro cultured calf hepatocytes and EVs were extracted from their supernatants as NK−derived EVs and CK−derived EVs, respectively. In vitro hepatocyte models, comprising a normal culture group (normal) and the group treated with NEFAs at 2.4 mM (2.4 NEFA), were treated with NK and CK−derived EVs. In addition, we transfected an SIRT1−overexpressing adenovirus into calf hepatocytes and determined the expression of key genes, enzymes, and proteins involved in the SIRT1/SREBP−1c/PGC−1α pathway. The results showed that the NK−derived EVs inhibited the expression of the SREBP−1c gene and protein and increased the expression of the SIRT1 and PGC−1α genes and proteins (p < 0.05). In contrast, CK−derived EVs induced lipid metabolism disorders in the normal hepatocyte group and aggravated NEFA-induced lipid metabolism imbalances in hepatocytes (p < 0.05). Moreover, overexpression of SIRT1 confirmed that EVs exert vital functions in hepatocyte lipid metabolism via SIRT1/SREBP−1c/PGC−1α signaling to regulate hepatocyte lipid metabolism. In summary, NK−derived EVs alleviated liver lipid metabolism disorders caused by NEFAs via modulation of SIRT1/SREBP−1c/PGC−1α signaling, while CK−derived EVs had the opposite effect. NK−derived EVs upregulated lipid oxidation-related genes and downregulated lipid synthesis-related genes, suggesting that NK−derived EVs could be used as biological extracts to alleviate lipid metabolism disorders in ketotic calf.