Starvation resistant cavefish reveal conserved mechanisms of starvation-induced hepatic lipotoxicity
Starvation is a severe form of malnutrition that occurs when an individual's intake of food is inadequate to meet their body's energy requirements. Prolonged starvation can cause permanent organ damage, stunted growth in children, and death if left untreated. It is estimated that approximately 45% of deaths among children under the age of 5 years are linked to undernutrition. Notably, the liver's health is compromised during starvation. More than 60 years ago, it was recognized that chronic severe malnutrition in children, such as kwashiorkor, leads to fatty liver. Subsequently, starvation has been shown to induce accumulation of liver fat (steatosis) in drosophila, zebrafish, and humans. To uncover potential strategies for protecting the liver, we turned to adaptation strategies present in a genetically tractable and naturally occurring model of starvation resistance - the Astyanax mexicanus model system. Cave populations of this species have adapted to survive in conditions of extreme starvation, while the surface populations of the same species display relatively normal vertebrate physiology. We took advantage of this unique system to study the response of the liver to starvation and identified reduced expression of the fatty acid uptake gene slc27a2a/fatp2 allowing cavefish to prevent liver damage under starvation. Targeting this pathway in both fish and flies mitigates starvation-induced hepatic steatosis and protects the liver from lipotoxicity in zebrafish. This demonstrates that the identified pathway is evolutionary conserved for over 400 million years, highlighting its potential as a druggable target. Overall design: For RNA-Seq, RNA was isolated from livers from fed and fasting animals. For this, livers from 40 larvae / replicate were dissected and collected in the lysis buffer from ReliaPrepTM RNA Miniprep Systems (Promega, Z6110). RNA was isolated from the lysed tissue by following the manufacture's instruction. cDNA synthesis, library preparation and Illumina sequencing was performed according to the manufacturer's instructions using the TruSeq Stranded mRNA Preparation Kit for Illumina (Ilumina #20020594). Purified libraries were quantified using a Quibit fluorometer (Life Technologies) and the quality assessed on the Agilent Bioanalyzer (Agilent Technologies). Sequencing was performed on the Illumina NextSeq 500 instrument as High Output with single-end 75bp reads. Following sequencing, raw reads were demultiplexed into Fastq format using Ilumina bclfastq2 v2.18. Raw reads were mapped using STAR aligner v2.7.3a against the UCSC genome astMex_2.0 genome, using Ensembl 102 gene models for annotations. Transcript abundance was quantified using RSEM v1.3.0.