A zebrafish forward genetic screen identifies an indispensable threonine residue in the kinase domain of PRKD2

A homozygous truncating mutation of FGL2 is associated with immune dysregulation

BACKGROUND

The type II transmembrane protein fibrinogen-like protein 2 (FGL2) plays critical roles in hemostasis and immune regulation. The C-terminal immunoregulatory domain of FGL2 can be secreted and is a mediator of regulatory T (Treg) cell suppression. Fgl2^-/- mice develop autoantibodies and glomerulonephritis and have impaired Treg cell function.

OBJECTIVE

Our aim was to identify the genetic underpinning and immune function in a patient with childhood onset of leukocytoclastic vasculitis, systemic inflammation, and autoantibodies.

METHODS

Whole-exome sequencing was performed on patient genomic DNA. FGL2 protein expression was examined in HEK293 transfected cells by immunoblotting and in PBMCs by flow cytometry. T follicular helper cells and Treg cells were examined by flow cytometry. Treg cell suppression of T-cell proliferation was assessed in vitro.

RESULTS

The patient had a homozygous mutation in FGL2 (c.614_617del:p.V205fs), which led to the expression of a truncated FGL2 protein that preserves the N-terminal domain but lacks the C-terminal immunoregulatory domain. The patient had an increased percentage of circulating T follicular helper and Treg cells. The patient's Treg cells had impaired in vitro suppressive ability that was rescued by the addition of full-length FGL2. Unlike full-length FGL2, the truncated FGL2^V205fs mutant failed to suppress T-cell proliferation.

CONCLUSIONS

We identified a homozygous mutation in FGL2 in a patient with immune dysregulation and impaired Treg cell function. Soluble FGL2 rescued the Treg cell defect, suggesting that it may provide a useful therapy for the patient.

First person – Panagiota Giardoglou and Despina Bournele

First Person is a series of interviews with the first authors of a selection of papers published in Biology Open, helping early-career researchers promote themselves alongside their papers. Panagiota Giardoglou and Despina Bournele are co-first authors on ‘A zebrafish forward genetic screen identifies an indispensable threonine residue in the kinase domain of PRKD2’, published in BiO. Panagiota is a PhD student in the lab of Dr Dimitris Beis at the Biomedical Research Foundation Academy of Athens, Greece, investigating modelling human cardiovascular diseases and underlying the mechanisms involved in their pathophysiology. Despina is a toxicologist in the lab of Dr Kyriaki Machera at the Benaki Phytopathological Institute, Kifissia, Athens, Greece, investigating molecular and developmental biology, and zebrafish toxicology.