Cancer-induced FOXP1 disrupts and reprograms skeletal muscle circadian transcription in cachexia [circadian RNA-seq]

Cancer cachexia is a debilitating metabolic disorder characterized by involuntary loss of body and muscle mass, leading to increased morbidity and mortality. We previously found that Forkhead box P1 (FoxP1) upregulation in skeletal muscle causes muscle wasting and is required for muscle wasting in response to cancer. However, transcriptional networks targeted by FoxP1 in skeletal muscles undergoing cancer-induced wasting remain largely unknown. Here, we identify FoxP1 as a key disruptor of the skeletal muscle clock in response to cancer, that reprograms circadian patterns of gene expression at cachexia onset. Specifically, we show that cancer-induced FoxP1 rewires the skeletal muscle circadian transcriptome towards pathways associated with muscle wasting and disrupts the temporal patterning of pathways governing glucose, lipid, and oxidative metabolism. These findings thus implicate cancer/disease-specific functions of FOXP1 in the disruption and reprograming of the skeletal muscle circadian transcriptome which may contribute to muscle wasting and the development of cachexia. Following an acclimation period to ensure entrainment to 12-hour light/dark cycle (lights on: 6 am), mice were kept in constant darkness for 18 hours (circadian time 0: CT0) in light-tight circadian cabinets. Tibialis anterior muscles were isolated and flash frozen in liquid nitrogen for RNA-sequencing from 39- to 55-week-old male homozygous FoxP1fl/fl x ACTA1-Cre (FoxP1SkmKO) mice and FoxP1fl/fl mice, as a FoxP1-expressing control and are referred to as wild type (WT) hereafter, with and without orthotopic murine KPC pancreatic tumors at CT 18, 22, 26, 30, 34, and 38 (n = 2 mice/condition/genotype/time point). RNA isolation was performed by homogenization of TA muscles in Trizol followed by extraction with chloroform, precipitation with isopropanol, and treatment with DNAse. RNA sequencing was performed by Novogene (Novogene Co, Ltd., Sacramento, CA).