Objective: We searched for genes whose alleles cause obesity and novel pathways correlated with obesity.
Research methods and procedures: BSB mice are a model of complex obesity due to interactions among genes from C57BL/6J (B) and Mus spretus (SPRET) in (B x SPRET) x B backcross mice. Stringent criteria identified 50 genes differentially expressed in epididymal adipose tissue from 7 pairs of lean vs. obese BSB mice. Quantitative reverse transcription-polymerase chain reaction of adipose tissue RNA from 48 BSB mice with a range of obesity was assayed. Leptin was evaluated in inbred (SPRET/Ei) and outbred (SPRET/Pt) BSB mice.
Results: Leptin (Lep) and adipsin expressions had the greatest fold differences between obese and lean mice. Four genes involved in iron homeostasis were included in the 50 differentially expressed genes [hemochromatosis (Hfe), diaphorase 1, transferrin receptor (Trfr) 2, and protoporphyrinogen oxidase] and two additional iron-related genes did not quite meet the stringent criteria for differential expression (Trfr and lactotransferrin). Hfe and Trfr mRNA levels and liver iron were negatively correlated with fat mass. Variation in obesity phenotypes explained 49%, 40%, and 37%, respectively, of the variance in Hfe, Lep, and Trfr mRNA levels. Leptin differed by haplotype at the Lep locus in outbred BSB. The quantitative trait locus identified in the outbred cross did not occur in inbred BSB.
Discussion: Our results suggest that iron homeostasis in BSB mice is coordinately regulated in vivo in adipose depots in response to obesity. Lep alleles derived from outbred, but not inbred, SPRET are a positional candidate for the chromosome 6 quantitative trait locus in BSB mice.