Genetic variability affects the development of brown adipocytes in white fat, but not in interscapular brown fat

Bingzhong Xue, Jong-Seop Rim, Jessica C Hogan, Ann A Coulter, Robert A Koza, and Leslie P Kozak

Pennington Biomedical Research Center, Baoon Rouge, LA 70808

Corresponding Author: Kozaklp{at}pbrc.edu

Cold exposure induces brown adipocytes in retroperitoneal (RP) white fat of adult A/J mice, but not in C57BL/6J (B6). In contrast, induction of the mitochondrial uncoupling protein 1 gene (Ucp1) in interscapular brown fat (iBAT) shows no strain dependence. We now show that unlike iBAT, in which Ucp1 expression was expressed in the fetus and continued to be expressed throughout life, Ucp1 in RP was transiently expressed between 10 and 30 days of age and then disappeared. Similar to the lack of genetic variation in expression of Ucp1 in iBAT during cold induction of adult mice, no genetic variation in Ucp1 expression in iBAT was detected during development. In contrast, UCP1-positive multilocular adipocytes, together with corresponding increases in Ucp1 expression, appeared in RP at 10 days of age in A/J and B6, but with much higher expression in A/J mice. At 20 days of age brown adipocytes represent the major adipocyte present in RP fat of A/J mice. The disappearance of brown adipocytes by 30 days of age suggested that tissue remodeling occurred in RP. Genetic variability in Ucp1 expression could not be explained by variation in expression of selective transcription factors and signaling molecules of adipogenesis. In summary, the existence of genetic variability between A/J and B6 mice during development of brown adipocyte expression in RP white fat, but not in iBAT, suggests that developmental mechanisms for the brown adipocyte differentiation program are different in these adipose tissues.

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