Ichthyosis associated with sphingosine 1-phosphate lyase insufficiency syndrome is due to aberrant calcium and sphingolipid regulation

Sphingosine 1-phosphate lyase (SGPL1) insufficiency (SPLIS) is a syndrome which presents with adrenal insufficiency, steroid resistant nephrotic syndrome, hypothyroidism, neurological disease, and ichthyosis. Where a skin phenotype is reported, 94% presented with abnormalities such as ichthyosis, acanthosis, and hyperpigmentation. To elucidate the disease mechanism and the role SGPL1 plays in the skin barrier we established CRISPR-Cas9 SGPL1 knock-out and a lentiviral induced SGPL1 overexpression in nTERT immortalised keratinocytes and thereafter organotypic skin equivalents. Loss of SGPL1 caused an accumulation of S1P, sphingosine and ceramide while its overexpression caused a reduction of these species. RNAseq analysis showed perturbations in sphingolipid pathway genes, particularly in SGPL1_KO and GSEA revealed polar opposite differential gene expression between SGPL1_KO and _OE in keratinocyte differentiation and Ca2+ signalling genesets. SGPL1_KO upregulated differentiation markers while SGPL1_OE upregulated basal and proliferative markers. The advanced differentiation of SGPL1_KO was confirmed by 3D organotypic models that also presented with a thickened and retained stratum corneum, sphingolipid accumulation in the spinous layer and a breakdown of E-cadherin junctions. We hypothesise that SPLIS associated ichthyosis is a multi-faceted disease caused by sphingolipid imbalance and excessive S1P signalling. We generated SGPL1 CRISPR KO nTERT cell lines as well as SGPL1 overexpressing cell lines and compared their transcriptomes using RNAseq. We used 3 biological replicates per group.