Nicastrin haploinsufficiency alters expression of type I interferon-stimulated genes: the relationship to familial hidradenitis suppurativa

Background: Hidradenitis suppurativa (HS), also called acne inversa, is a chronic skin disease. The symptoms can be severe, and include intensely painful nodules and abscesses in apocrine-gland rich inverse skin, such as the buttocks, under the arms and in the groin. Autosomal dominant forms of HS exist, but are rare. Some of these kindred have heterozygous loss-of-function rare variants in the γ-secretase complex component nicastrin (NCSTN). Aim: To investigate the effect of NCSTN haploinsufficiency on human keratinocytes and assess potential mechanisms for lesion development. Methods: NCSTN was knocked down using a small hairpin RNA construct in both a keratinocyte cell line (HEK001) and an embryonic kidney cell line (HEK293), and differential gene expression was assessed using RNA microarray. Using the HEK293 line, a heterozygous deletion of NCSTN was created with CRISPR/Cas9 genome editing, and nuclear factor kappa B activity was assessed using a luciferase reporter. Results: Compared with controls, the keratinocyte NCSTN knockdown cell line showed a significantly increased expression of genes related to the type I interferon response pathway. Both HEK001 and HEK293 knockdowns demonstrated evidence of altered growth. There was a small but significant increase in nuclear factor kappa B signalling in response to tumour necrosis factor treatment in HEK293 cells genome-edited for reduced NCSTN. Conclusions: Our data suggest a role for increased keratinocyte inflammatory responsiveness in familial HS. Confirming this phenotype and characterizing additional effects in different cell types will require study beyond cell lines, such as in primary cells and tissues.