Decreased Skin Barrier Lipid Acylceramide and Differentiation-Dependent Gene Expression in Ichthyosis Gene Nipal4-Knockout Mice

Abstract

NIPAL4 is one of the causative genes for autosomal recessive congenital ichthyosis. However, the role of NIPAL4 in skin barrier formation and the molecular mechanism of ichthyosis pathology caused by NIPAL4 mutations, have not yet been determined. Here, we found that Nipal4-knockout (KO) mice exhibited neonatal lethality due to skin barrier defects. Histological analyses showed several morphological abnormalities in the Nipal4-KO epidermis, including impairment of lipid multilayer structure formation, hyperkeratosis, immature keratohyalin granules, and developed heterochromatin structures. The levels of the skin barrier lipid acylceramide were decreased in Nipal4-KO mice. Expression of genes involved in skin barrier formation normally increases during keratinocyte differentiation, in which chromatin remodeling is involved. However, the induction of Krt1, Lor, Flg, Elovl1, and Dgat2 was impaired in Nipal4-KO mice. NIPAL4 is a putative Mg transporter, and Mg concentration in differentiated keratinocytes of Nipal4-KO mice was indeed lower than that of wild-type mice. Our results suggest that low Mg concentration causes aberration in the proper chromatin remodeling process, which in turn leads to failure of differentiation-dependent gene induction in keratinocytes. Our findings provide insights into Mg-dependent regulation of gene expression and skin barrier formation during keratinocyte differentiation.

Severe Skin Permeability Barrier Dysfunction in Knockout Mice Deficient in a Fatty Acid ω-Hydroxylase Crucial to Acylceramide Production

“…The skin of the E18.5 mice was prepared and analyzed by hematoxylin and eosin staining or transmission electron microscopy, according to methods described previously (Honda et al, 2018;Naganuma et al, 2016).…”

“…To date, 10 genes have been identified as causative of ARCI (Hotz et al, 2018;Sugiura and Akiyama, 2015), of which three (CERS3, CYP4F22, and PNPLA1) are involved in acylceramide synthesis (Hirabayashi et al, 2019;Kihara, 2016) and two (ALOXE3 and ALOX12B) are involved in the conversion of acylceramide to protein-bound ceramide (Supplementary Figure S1) (Zheng et al, 2011). Mutations in these genes cause lamellar ichthyosis or congenital ichthyosiform erythroderma (Sugiura and Akiyama, 2015), and mutations in other genes involved in acylceramide production (ELOVL1, ELOVL4, and ABHD5) cause syndromic types of ichthyoses (Aldahmesh et al, 2011;Kutkowska-Ka zmierczak et al, 2018;Mueller et al, 2019;Ohno et al, 2018;Sassa et al, 2013;Vasireddy et al, 2007). Except for CYP4F22, knockout (KO) mice deficient in each of these acylceramiderelated genes have already been created and analyzed (Grond et al, 2017;Hirabayashi et al, 2017;Jennemann et al, 2012;Pichery et al, 2017;Radner et al, 2010;Sassa et al, 2013;Vasireddy et al, 2007); all exhibit neonatal lethality because of skin barrier abnormalities, confirming the important role of acylceramide in skin barrier formation.…”

Molecular Mechanism of Epidermal Barrier Dysfunction as Primary Abnormalities

“…Loss-of-function mutations in NIPAL4 (NIPA like domain containing 4) cause autosomal recessive congenital ichthyosis. Acylceramide levels are reduced with impaired lipid multilayer structure formation in Nipal4-knockout mice, which indicates the role of NIPAL4 deficiency in epidermal barrier defects [77]. CYP4F22 is a fatty acid ω-hydroxylase involved in the synthesis of acylceramide.…”

LGI3 promotes human keratinocyte differentiation via the Akt pathway

“…Dysfunction of the skin barrier is a major characteristic of skin disorders such as psoriasis, atopic dermatitis and ichthyosis . Although those diseases are classified as inflammatory disorders, epidermal barrier insult has been reported to contribute to each of them through the induction of innate and adaptive immunity . Therefore, recovery of the skin barrier can be a therapeutic target for those disorders.…”

“…Normal skin tissue expresses appropriate levels of differentiation markers to produce a substantial skin barrier. However, differentiation markers are downregulated in psoriasis, atopic dermatitis and ichthyosis, which causes keratinocytes to lose their barrier function and allows external stimuli to induce skin inflammation . Therefore, enhanced differentiation of keratinocytes could be a key component of treatment for skin barrier dysfunction because increased differentiation reduces skin inflammation through the recovery of skin barrier function.…”