Polysome Profiling in Liver Identifies Dynamic Regulation of Endoplasmic Reticulum Translatome by Obesity and Fasting

Abstract

Obesity-associated metabolic complications are generally considered to emerge from abnormalities in carbohydrate and lipid metabolism, whereas the status of protein metabolism is not well studied. Here, we performed comparative polysome and associated transcriptional profiling analyses to study the dynamics and functional implications of endoplasmic reticulum (ER)–associated protein synthesis in the mouse liver under conditions of obesity and nutrient deprivation. We discovered that ER from livers of obese mice exhibits a general reduction in protein synthesis, and comprehensive analysis of polysome-bound transcripts revealed extensive down-regulation of protein synthesis machinery, mitochondrial components, and bile acid metabolism in the obese translatome. Nutrient availability also plays an important but distinct role in remodeling the hepatic ER translatome in lean and obese mice. Fasting in obese mice partially reversed the overall translatomic differences between lean and obese nonfasted controls, whereas fasting of the lean mice mimicked many of the translatomic changes induced by the development of obesity. The strongest examples of such regulations were the reduction in Cyp7b1 and Slco1a1, molecules involved in bile acid metabolism. Exogenous expression of either gene significantly lowered plasma glucose levels, improved hepatic steatosis, but also caused cholestasis, indicating the fine balance bile acids play in regulating metabolism and health. Together, our work defines dynamic regulation of the liver translatome by obesity and nutrient availability, and it identifies a novel role for bile acid metabolism in the pathogenesis of metabolic abnormalities associated with obesity.

ALOX5AP Overexpression in Adipose Tissue Leads to LXA4 Production and Protection Against Diet-Induced Obesity and Insulin Resistance

“…This improvement may be, at least partially, due to the leaner phenotype of these mice, associated with decreased lipid accumulation in nonadipose tissues and decreased inflammation in WAT. The increase in Cyp7b1 hepatic expression observed in transgenic mice may also have contributed to their protection against diet-induced glucose intolerance and hepatic steatosis, as suggested by the beneficial effects of hepatic Cyp7b1 overexpression on these parameters previously reported (60).…”

Quantitative analysis of the murine lipid droplet-associated proteome during diet-induced hepatic steatosis

“…screens have found that the knockdown of ribosomal proteins increases LD storage ( 63,64 ). In obese mouse livers, ER-associated protein synthesis and the number of ribosome proteins bound to the ER membrane were found to be decreased, while lipid metabolism was increased ( 65,66 ). It has been postulated that LDs provide a reservoir for unfolded proteins and toxic lipids from the ER, because during times of ER dysfunction, LDs accumulate ( 67 ).…”

High-fat diet caused widespread epigenomic differences on hepatic methylome in rat

“…The quantitative (q)PCR efficiency was calculated based on the slope from each individual run (https://www.lifetechnologies.com/us/en/home/ brands/thermo-scientific/molecular-biology/molecular-biology-learningcenter/molecular-biology-resource-library/thermo-scientific-web-tools/ qpcr-efficiency-calculator.html). 18S ribosomal RNA was used as a reference gene (13,14,16) for the normalization in qPCR, the expression of which didn't differ by treatment. A no-template control omits any cDNA template from a reaction and a no-reverse transcriptase control were two negative controls included in our experiments.…”