# Proteomic Analysis of Protein Ubiquitination Events in Dairy Goats with Fatty Liver

## TL;DR

This study identifies changes in protein ubiquitination in dairy goats with fatty liver, linking these changes to lipid metabolism pathways and offering new insights into the disease's development.

## Contribution

The study is the first to profile hepatic protein ubiquitination in dairy goats with fatty liver, revealing novel insights into its metabolic regulation.

## Key findings

- 238 ubiquitination sites across 921 proteins were differentially altered in fatty liver goats.
- Downregulated ubiquitination sites were enriched in lipid metabolism pathways like PPAR signaling and fatty acid degradation.
- Proteins with reduced ubiquitination were transcriptionally upregulated in fatty liver goats, suggesting complex regulatory mechanisms.

## Abstract

This study examined the hepatic protein ubiquitination profiles of periparturient dairy goats with fatty liver, a major metabolic disorder. Liver and blood samples were collected from healthy goats (Con, n = 3) and goats with fatty liver (FL, n = 3) and subjected to quantitative proteomics and bioinformatics analysis. FL goats exhibited elevated serum levels of β-hydroxybutyric acid (BHBA) and non-esterified fatty acids (NEFA), and histological analysis revealed extensive vacuolar degeneration and higher triglyceride levels in their hepatic tissues. In total, 238 differentially altered ubiquitination sites were identified across 921 proteins in FL goats, with 351 sites being upregulated and 570 sites being downregulated. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses showed that these proteins were enriched in lipid metabolism pathways, including PPAR signaling, fatty acid degradation, and peroxisome activity. Notably, proteins with downregulated ubiquitination (e.g., ACSL1, ACSL5, EHHADH, ACAA1) were transcriptionally upregulated in FL goats. These results highlight the critical role of ubiquitination in the pathogenesis of fatty liver and offer insights for future research on metabolic regulation in dairy goats.

Fatty liver is a major metabolic disease in periparturient dairy goats. Protein ubiquitination, a type of dynamic and multifaceted post-translational modification, plays an important role in metabolism by regulating the stability and function of target proteins. However, the hepatic protein ubiquitination profile in dairy goats with fatty liver is yet to be elucidated. In this study, we collected liver and blood samples from healthy dairy goats (Con, n = 3) and dairy goats with fatty liver (FL, n = 3). Then, we analyzed the overall ubiquitination of hepatic proteins in dairy goats with fatty liver through quantitative ubiquitin label-free proteomics and bioinformatics. Proteins showing significantly altered levels of ubiquitination were identified via bioinformatics, and related regulatory pathways were screened. The results showed that the blood levels of beta-hydroxybutyric acid and non-esterified fatty acids were significantly upregulated in dairy goats with fatty liver, and a total of 238 ubiquitination sites across 921 proteins were found to be differentially altered in the fatty liver group. Among them, ubiquitination was upregulated at 351 sites across 93 proteins and downregulated at 570 sites across 145 proteins. In addition, GO and KEGG pathway analysis revealed that the differentially ubiquitinated proteins were enriched in pathways regulating lipid metabolism, such as the PPAR signaling pathway, fatty acid degradation, and peroxisome activity. Notably, by observing the overlap among these three sub-networks, we found that proteins with downregulated ubiquitination—such as ACSL1, ACSL5, EHHADH, and ACAA1—were transcriptionally upregulated in dairy goats with fatty liver. This study reveals the key ubiquitinated proteins in dairy goats with fatty liver and provides a more comprehensive understanding of the pathogenesis of fatty liver in dairy goats.