Engineering of genetic variants in complex disease pathophysiology

Genetic risk factors that contribute to atopic dermatitis onset and disease severity have been identified over a decade ago. For example, loss-of-function mutations in the filaggrin gene are widely reported and studied. However, intra-individual genomic predisposition, immunological confounders, and environmental interactions complicate the comparison between filaggrin genotypes and related causal effects. Genetic engineering of skin cells (keratinocytes) brought us one step closer to understanding the actual contribution of filaggrin genetic variants to atopic dermatitis.

Researcher Jos P.H. Smits and colleagues harnessed CRISPR/Cas9 genomic engineering of human skin cells (keratinocytes) to generate filaggrin knockout keratinocytes. By doing so, the research group was able to study the phenotype of filaggrin knockout in contrast to filaggrin wildtype keratinocytes within a furthermore identical genetic and immunologic background. The research group, led by Ellen van den Bogaard published their results in the Journal of Investigative Dermatology this month.

Following the knockout of filaggrin, the research group studied the filaggrin null phenotype by growing three-dimensional (3D) epidermal equivalents and analyzing their morphology, barrier protein expression, and skin barrier functionality. Filaggrin is known for its role in the physical skin barrier by undergoing proteolytic degradation where its amino acids eventually form the hydrophobic protection against our environment. Unexpectedly, besides the loss of filaggrin protein and the diminished skin barrier properties, other structural proteins were affected. CRISPR/Cas9 was subsequently used to repair filaggrin expression and resulted in recovery of the wildtype phenotype, indicating that filaggrin itself potentially has an unidentified function in the skin.

This work has been the basis of a successful LEO foundation research grant application to Jos and Ellen enabling their group to grow and expand their research line towards a better understanding of genotype-phenotype correlations in complex multifactorial skin diseases with a high disease burden and find novel drug targets or therapeutic modes of action.

Read the study here: Investigations into the filaggrin null phenotype: showcasing the methodology for CRISPR/Cas9 editing of human keratinocytes (jidonline.org) Jos P.H. Smits, Noa J.M. van den Brink, Luca D. Meesters, Hadia Hamdaoui, Hanna Niehues, Patrick A.M. Jansen, Ivonne M.J.J. van Vlijmen-Willems, Diana Rodijk-Olthuis, Céline Evrard, Yves Poumay, Michel van Geel, Wiljan J.A.J. Hendriks, Joost Schalkwijk, Patrick  L.J.M. Zeeuwen, Ellen H. van den Bogaard. Published:March 07, 2023DOI:https://doi.org/10.1016/j.jid.2023.02.021
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