Abstract 4836: Fasting induces greater expression of mitochondrial proteins associated with fatty acid metabolism and non-shivering thermogenesis in brown adipose tissue of knock-in ACSS1K635Q mice
Authors: Gargapati Aishani Sivasai , Varmazyad Mahboubeh , Gius David 
Published: June 2023

Introduction: Acyl-CoA Synthetase Short Chain Family Member 1 (ACSS1) is an important mitochondrial enzyme for the production of ATP from short chain fatty acids under energetic stress. ACSS1 is highly expressed in brown adipose tissue, heart, and skeletal muscle. ACSS1 is regulated in part by a post-translational modification of ACSS1, whereby the side chain of Lysine-635 is acetylated. The activity of ACSS1 is downregulated by the acetylation of Lysine-635. The downregulation of ACSS1 activity has been shown to impose changes on fatty acid metabolism and body temperature. Our lab observed that homozygous knock-in ACSS1 mice that fasted for 48 hours were hypothermic with a temperature of 30 °C. Here, we utilized mutant mice to simulate acetylated ACSS1, to investigate the role of ACSS1K635Q in mitochondrial fatty acid metabolism and maintenance of body temperature under fasting conditions.

Methods: A knock-in ACSS1 mouse model with a mutation of ACSS1K635Q was designed to model the downregulation of ACSS1. Wild Type mice and Homozygous Knock-in ACSS1K635Q mice were either fasted for 48 hours (F48) or fed with a normal diet (ND). Four experimental groups - Wild Type ND and F48 mice and Homozygous Knock-in ACSS1K635Q ND and F48 mice - were examined. Protein was extracted from 10 samples each containing 20 mg of brown adipose tissue. Tissue samples were lysed and immunoblotted with primary and secondary antibodies. Western Blot Western Blot was performed on the proteins Uncoupling Protein 1 (UCP1), UCP2, ACC, and AMPK. Membranes were imaged using the FluorChem M system, and chemiluminescence was quantified using the NIH ImageJ software. ANOVA and t-test were used to conduct statistical analysis (P &lt; 0.05).

Results: Homozygous Ki-ACSS1K635Q F48 mice expressed higher levels of UCP1 and UCP2 in BAT than Homozygous Ki-ACSS1K635Q ND mice. We observed a greater difference in UCP1 expression between Homozygous Ki-CSS1K635Q ND and F48 mice compared to the difference in UCP1 expression between Wild Type ND and F48 mice. In Wild Type and Homozygous Ki-ACSS1K635Q mice, UCP1 expression was lower than UCP2 expression. Fasting for 48 hours significantly upregulated p-AMPK in Wild Type mice.

Conclusions: Under fasting conditions, metabolic processes may shift towards a greater proportion of non-shivering thermogenesis due to ACSS1 inactivity. UCP1 likely contributes more to non-shivering thermogenesis than UCP2. Understanding the impact of acetylating ACSS1 provides avenues towards developing personalized treatments that effectively respond to metabolic stressors.

Citation Format: Aishani Sivasai Gargapati, Mahboubeh Varmazyad, David Gius. Fasting induces greater expression of mitochondrial proteins associated with fatty acid metabolism and non-shivering thermogenesis in brown adipose tissue of knock-in ACSS1K635Q mice. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 4836.