Fatty acid transport protein 1 can compensate for fatty acid transport protein 4 in the developing mouse epidermis - PubMed (original) (raw)

Fatty acid transport protein 1 can compensate for fatty acid transport protein 4 in the developing mouse epidermis

Meei-Hua Lin et al. J Invest Dermatol. 2015 Feb.

Abstract

Fatty acid transport protein (FATP) 4 is one of a family of six FATPs that facilitate long- and very-long-chain fatty acid uptake. Mice lacking FATP4 are born with tight, thick skin and a defective barrier; they die neonatally because of dehydration and restricted movements. Mutations in SLC27A4, the gene encoding FATP4, cause ichthyosis prematurity syndrome (IPS), characterized by premature birth, respiratory distress, and edematous skin with severe ichthyotic scaling. Symptoms of surviving patients become mild, although atopic manifestations are common. We previously showed that suprabasal keratinocyte expression of a Fatp4 transgene in Fatp4 mutant skin rescues the lethality and ameliorates the skin phenotype. Here we tested the hypothesis that FATP1, the closest FATP4 homolog, can compensate for the lack of FATP4 in our mouse model of IPS, as it might do postnatally in IPS patients. Transgenic expression of FATP1 in suprabasal keratinocytes rescued the phenotype of Fatp4 mutants, and FATP1 sorted to the same intracellular organelles as endogenous FATP4. Thus, FATP1 and FATP4 likely have overlapping substrate specificities, enzymatic activities, and biological functions. These results suggest that increasing expression of FATP1 in suprabasal keratinocytes could normalize the skin of IPS patients and perhaps prevent the atopic manifestations.

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Conflict of interest statement

CONFLICT OF INTEREST

None to disclose

Figures

Figure 1. Restoration of the skin barrier in _Fatp4_−/−;Tg(IVL-Fatp1) and _Fatp4_−/−;Tg(IVL-Fatp4) mice

(a) Dorsal skin sections from E16.0 littermate embryos were subjected to in situ hybridization and counterstained with nuclear fast red. Fatp4 RNA was detected in suprabasal keratinocytes of Fatp4+/− (control) and in nuclei of some Fatp4−/− keratinocytes (top panels). Fatp1 RNA was detected in basal keratinocytes and hair follicle (asterisks) progenitors of Fatp4+/− and Fatp4−/− embryos, and additionally detected in suprabasal keratinocytes of Fatp4−/−;Tg(IVL-Fatp1) embryos (lower panels). Dashed lines demarcate the dermo-epidermal boundary. Scale bar is 50 μm. (b) E17.5 littermate embryos were tested for inward X-Gal permeability. The incomplete barrier in Fatp4−/− embryos was remedied in Fatp4−/−;Tg(IVL-Fatp1) embryos (asterisk). (c, d) Newborns were tested for outward TEWL assays. The increased TEWL in Fatp4−/− newborns compared to Fatp4+/− controls was normalized in both Fatp4−/−;Tg(IVL-Fatp1) (c) and Fatp4−/−;Tg(IVL-Fatp4) newborns (d). Numbers of samples (n) are indicated. ***P<0.001; *P<0.05. The TEWL readings in c and d were obtained from two separate Vapometers.

Figure 2. Amelioration of skin phenotypes in _Fatp4_−/−;Tg(IVL-Fatp1) mice

Dorsal skin sections from E16.0 embryo littermates were subjected to hematoxylin and eosin staining (top row) and immunohistochemical analyses followed by counterstaining with hematoxylin (bottom three rows). The thickened epidermis phenotype seen in Fatp4−/− newborns was normalized in Fatp4−/−;Tg(IVL-Fatp1) newborns (top row). The HA-tagged FATP1 encoded by the transgene was detected primarily in granular keratinocytes in Fatp4−/−;Tg(IVL-Fatp1) mice (second row). The ectopic expression of keratin 6 seen in Fatp4−/− newborns was diminished in Fatp4−/−;Tg(IVL-Fatp1) mice (third row). The nuclear localization of pSTAT3 shown in Fatp4−/− newborns was also diminished in Fatp4−/−;Tg(IVL-Fatp1) mice (bottom row). Dashed lines demarcate the dermo-epidermal boundary. Scale bar is 50 μm.

Figure 3. Amelioration of the elevated level of free fatty acids in _Fatp4_−/−;Tg(IVL-Fatp1) and _Fatp4_−/−;Tg(IVL-Fatp4) epidermis

Free, extractable lipids from the epidermis of newborn mice were resolved by TLC and visualized by charring the plate. The elevated level of free fatty acids seen in Fatp4−/− mice was reduced to normal in Fatp4−/−;Tg(IVL-Fatp1) (a) and Fatp4−/−;Tg(IVL-Fatp4) mice (b). Components of the lipid standards and origin of sample application are indicated on the left of a. Lipid species of the epidermis are indicated between the panels.

Figure 4. Restoration of the keratohyalin granules in _Fatp4_−/−;Tg(IVL-Fatp4) and _Fatp4_−/−;Tg(IVL-Fatp1) mice

Granular keratinocytes-enriched cell fractions were prepared from the epidermis of newborn littermates and stained with hematoxylin. The smaller cell size and less distinct keratohyalin granules seen in Fatp4−/− mice compared to control (Fatp4+/−) were normalized in Fatp4−/−;Tg(IVL-Fatp4) and Fatp4−/−;Tg(IVL-Fatp1) mice. Scale bar is 10 μm.

Figure 5. Subcellular localization of endogenous FATP4 and transgenic FATP1 in granular keratinocytes

Granular keratinocytes from the epidermis of newborns (a–i′, m–o′) or 1.5 (j–l′) or 5.5-day-old (p–u′) pups were subjected to double immunofluorescence staining with the indicated antibodies. Merged confocal images of low and high magnification are shown in the right two columns. The mesh-like pattern of FATP4 staining in Fatp4+/+ cells colocalized partially with the mitochondrial membrane protein ATP synthase (a–c′; arrowheads in c′) and mainly with the ER luminal protein calreticulin (d–f′), but not with the plasma membrane protein interleukin 1 receptor 1 (g–i′). The mesh-like pattern of FATP4 localization was similar to the staining pattern of calreticulin around the filaggrin-positive granules (j–l′). The HA-tagged FATP1 in Fatp4+/+;Tg(IVL-Fatp1) cells also showed a mesh-like staining pattern that colocalized with endogenous FATP4 (s–u′). The HA-tagged FATP1 was not detected in Fatp4+/+ cells (m–o′). Endogenous FATP4 was not detected in Fatp4−/−;Tg(IVL-Fatp1) cells (p–r′). Scale bar is 10 μm.

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Fatty acid transport protein 1 can compensate for fatty acid transport protein 4 in the developing mouse epidermis - PubMed (original) (raw)