Wt1 haploinsufficiency induces browning of epididymal fat and alleviates metabolic dysfunction in mice on high-fat diet

Abstract

Aims/hypothesis Despite a similar fat storing function, visceral (intra-abdominal) white adipose tissue (WAT) is detrimental, whereas subcutaneous WAT is considered to protect against metabolic disease. Recent findings indicate that thermogenic genes, expressed in brown adipose tissue (BAT), can be induced primarily in subcutaneous WAT. Here, we investigate the hypothesis that the Wilms tumour gene product (WT1), which is expressed in intra-abdominal WAT but not in subcutaneous WAT and BAT, suppresses a thermogenic program in white fat cells. Methods Heterozygous Wt1 knockout mice and their wild-type littermates were examined in terms of thermogenic and adipocyte-selective gene expression. Glucose tolerance and hepatic lipid accumulation in these mice were assessed under normal chow and high-fat diet conditions. Pre-adipocytes isolated from the stromal vascular fraction of BAT were transduced with Wt1-expressing retrovirus, induced to differentiate and analysed for the expression of thermogenic and adipocyte-selective genes. Results Expression of the thermogenic genes Cpt1b and Tmem26 was enhanced and transcript levels of Ucp1 were on average more than tenfold higher in epididymal WAT of heterozygous Wt1 knockout mice compared with wild-type mice. Wt1 heterozygosity reduced epididymal WAT mass, improved whole-body glucose tolerance and alleviated severe hepatic steatosis upon diet-induced obesity in mice. Retroviral expression of WT1 in brown pre-adipocytes, which lack endogenous WT1, reduced mRNA levels of Ucp1, Ppargc1a, Cidea, Prdm16 and Cpt1b upon in vitro differentiation by 60–90%. WT1 knockdown in epididymal pre-adipocytes significantly lowered Aldh1a1 and Zfp423 transcripts, two key suppressors of the thermogenic program. Conversely, Aldh1a1 and Zfp423 mRNA levels were increased approximately five- and threefold, respectively, by retroviral expression of WT1 in brown pre-adipocytes. Conclusion/interpretation WT1 functions as a white adipocyte determination factor in epididymal WAT by suppressing thermogenic genes. Reducing Wt1 expression in this and other intra-abdominal fat depots may represent a novel treatment strategy in metabolic disease. Graphical abstract

WT1 in Adipose Tissue: From Development to Adult Physiology

“…Retroviral delivery of WT1 repressed thermogenic genes upon in vitro differentiation of immortalized brown preadipocytes. ( Kirschner et al, 2022 ). Likewise, overexpression of Wt1 reduced Ucp1, Ppargc1a, Cidea, Prdm16 and Cpt1b transcripts in differentiating Sca1 + :CD45 − :CD31 − preadipocytes isolated from the interscapular BAT of mice .…”

“…Likewise, overexpression of Wt1 reduced Ucp1, Ppargc1a, Cidea, Prdm16 and Cpt1b transcripts in differentiating Sca1 + :CD45 − :CD31 − preadipocytes isolated from the interscapular BAT of mice . ( Kirschner et al, 2022 ). WT1 caused no changes of adipocyte-selective genes that are expressed in both, white and brown fat cells.…”

“…WT1 also did not interfere with overall adipogenic differentiation assessed in terms of intracellular lipid storage. ( Kirschner et al, 2022 ). These findings let us conclude that ectopic WT1 suppresses the genetic signature of brown adipocytes.…”

“…Heterozygous Wt1 knockout mice show morphological and molecular signs of browning in their visceral (epididymal) WAT. ( Kirschner et al, 2022 ). It is currently unknown whether epididymal WAT browning is restricted to adipocytes originating from WT1 expressing progenitor cells (blue) as drawn in the figure, or also includes WT1-negative cells (pink).…”

“…The marked multilocular fat deposition in beige adipocytes is drawn for the sake of clarity but not seen in heterozygous Wt1 knockout mice. ( Kirschner et al, 2022 ). Adapted with modifications from ref.…”