Type 2 diabetes (T2D) and metabolic dysfunction-associated steatotic liver disease (MASLD) are increasingly prevalent and coexisting conditions. If untreated, MASLD progresses from simple steatosis to steatohepatitis, cirrhosis, or hepatocellular carcinoma, increasing T2D risk. Conversely, T2D, characterised by insulin resistance and chronic hyperglycemia, accelerates MASLD progression. Emerging evidence links these conditions with protein lysine acetylation (Kac), a reversible post-translational modification where acetyl-coenzyme A donates acetyl groups to the epsilon-amino group of lysine residues. However, the role of Kac in T2D-associated MASLD remains poorly characterised.
Thus, we induced T2D in 8-week-old male Sprague-Dawley rats using a high-fat diet (HFD) and low-dose streptozotocin (STZ), generating four cohorts with controls for each treatment. Alongside fasting blood glucose quantitation, plasma insulin, triglyceride, alanine transaminase (ALT), and aspartate aminotransferase (AST) levels were determined via colourimetry (n≥6/group). Assessments of microvesicular and macrovesicular steatosis were performed on haematoxylin and eosin-stained rat liver sections (n≥7/group) using QuPath. Western blotting with anti-acetyl-lysine antibodies was performed to examine hepatic Kac (n≥8/group). This was complemented by quantitative proteomics of the hepatic lysine acetylome using matched liver samples (n=4/group), anti-acetyl-lysine antibody-conjugated agarose beads, and two-dimensional liquid chromatography-tandem mass spectrometry.
Our findings show that HFD and STZ synergistically elevated fasting blood glucose and plasma insulin, triglyceride, and ALT levels. While STZ alone raised plasma ALT and AST levels, HFD alone did not impact these hepatic injury biomarkers. Histological assessment unveiled distinct histological patterns: STZ-induced hyperglycaemia promoted hepatic microvesicular steatosis, HFD-induced obesity and dyslipidaemia led to hepatic macrovesicular steatosis, and their combination generated mixed steatosis and fewer physiological hepatocytes. Western blotting revealed this coincided with synergistically elevated levels of global hepatic Kac in the HFD-STZ cohort, contrasting with HFD-induced hypoacetylation or STZ-induced hyperacetylation.
Overall, we defined a hepatic signature that reflects cellular and post-translational adaptations mediating the MASLD-T2D nexus.