Keratinocyte-specific Expression of Fatty Acid Transport Protein 4 Rescues the Wrinkle-free Phenotype in Slc27a4/Fatp4 Mutant Mice

Abstract

FATP4 (fatty acid transport protein 4; also known as SLC27A4) is the most widely expressed member of a family of six long chain fatty acid transporters. FATP4 is highly expressed in enterocytes and has therefore been proposed to be a major importer of dietary fatty acids. Two independent mutations in Fatp4 cause mice to be born with thick, tight, shiny, "wrinklefree" skin and a defective skin barrier; they die within hours of birth from dehydration and restricted movements. In contrast, induced keratinocyte-specific deficiency of FATP4 in adult mice causes only mild skin abnormalities. Therefore, whether the loss of FATP4 from skin or a systemic gestational metabolic defect causes the severe skin defects and neonatal lethality remain important unanswered questions. To investigate the basis for the phenotype, we first generated wild-type tetraploid/mutant diploid aggregates that should lead to rescue of any abnormalities caused by loss of FATP4 from the placenta. However, the skin phenotype was not ameliorated. We then generated transgenic mice expressing exogenous FATP4 either widely or specifically in suprabasal keratinocytes, and we bred the transgenes onto the Fatp4 ؊/؊ background. Both modes of FATP4 expression led to rescue of the neonatally lethal skin defects, and the resulting mice were viable and fertile. Keratinocyte expression of an FATP4 variant with mutations in the acyl-CoA synthetase domain did not provide any degree of rescue. We conclude that expression of FATP4 with an intact acyl-CoA synthetase domain in suprabasal keratinocytes is necessary for normal skin development and that FATP4 functions in establishing the cornified envelope. Fatty acid transport proteins (FATPs)2 compose a family of transmembrane proteins that facilitate cellular long chain fatty acid uptake (1-3). The most widely expressed member of this family is FATP4 (4, 5), which is encoded by Slc27a4 (solute carrier family 27 member 4 gene). The most robust expression of FATP4 is in intestinal epithelial cells (5), but its broad expression pattern is suggestive of functions in many organs.Surprisingly, the "wrinkle-free" phenotype we discovered in mice with a spontaneous mutation in Slc27a4 (Slc27a4 wrfr ) and the identical phenotype of mice with a targeted Slc27a4 mutation (Slc27a4) indicate critical roles for FATP4 in skin and hair development (6, 7). For these mutations, which both affect exon 3, homozygotes are born with tight, thick, shiny skin and a defective skin barrier; they die shortly after birth because of restricted movements and dehydration. These defects are reminiscent of human restrictive dermopathy, but this disease has recently been linked to mutations in zinc metalloproteinase STE24 (8 -10). Interestingly, deletion of Slc27a4 exons 2 and 3 (the first two coding exons; Slc27a4 tm1Asta ) results in embryonic lethality prior to embryonic day 9.5 (11). The reason for the striking difference in phenotypes remains unknown, but it may involve a partially functional truncated protein in the first two mutants or early ...

Fatty acid transport protein 4 is dispensable for intestinal lipid absorption in mice

“…1F). These data confirm that Fatp4 2/2 ;Ivl-Fatp4 tg/1 mice express neither endogenous nor transgenic FATP4 mRNA (15) or protein in the small intestine and suggest that there is no gradient of FATP4 expression in the intestine of wild-type mice. Furthermore, there was no change in FATP4 mRNA or protein expression in the intestine of wild-type mice fed a range of fat and/or cholesterol supplemented diets (including Western, high cholesterol, or high saturated fat), compared with mice fed a low-fat, low-cholesterol, chow diet (data not shown).…”

“…2/2 ;Ivl-Fatp4 tg/1 mice were generated as described and maintained on a mixed 129/B6/CBA strain background (15). Both Fatp4 1/2 ;Ivl-Fatp4 tg/1 and Fatp4 1/2 or Fatp4 1/1 mice (without the Ivl-Fatp4 transgene) were used as control mice, with no difference in phenotype observed between these genotypes.…”

“…A portion of the organic phase was dried and resuspended in 1% Triton X-100 for enzymatic determination of tissue lipid content. Western blotting and immunohistochemical staining of intestinal extracts or tissues for FATP4 was conducted as detailed (15).…”

“…The perinatal lethality appears to be due exclusively to absence of FATP4 in skin, as knockout mice can be rescued by transgenic expression of FATP4 from a keratinocyte specific promoter, yielding mice (Fatp4 2/2 ;Ivl-Fatp4 tg/1 mice) that are viable and have only a mild skin/hair phenotype (15). Because Fatp4 2/2 ; Ivl-Fatp4 tg/1 mice lacking FATP4 in the intestine suckle normally and develop to adulthood, it was unclear to what extent the presence of FATP4 in the intestine is required for normal fat absorption.…”

Thematic review series: Skin Lipids. The role of epidermal lipids in cutaneous permeability barrier homeostasis

“…Of note is that mice with spontaneous mutations in FATP4 or certain targeted disruptions of FATP4 display a restrictive dermopathy and a markedly defective permeability barrier function, which leads to death soon after birth (161,162). Notably, transgenic mice that overexpress FATP4 only in the epidermis can rescue mice with a spontaneous mutation in FATP4 (163).…”