Genetic Deletion of Polo-Like Kinase 2 Induces a Pro-Fibrotic Pulmonary Phenotype

Abstract

Pulmonary fibrosis is the chronic-progressive replacement of healthy lung tissue by extracellular matrix, leading to the destruction of the alveolar architecture and ultimately death. Due to limited pathophysiological knowledge, causal therapies are still missing and consequently the prognosis is poor. Thus, there is an urgent clinical need for models to derive effective therapies. Polo-like kinase 2 (PLK2) is an emerging regulator of fibroblast function and fibrosis. We found a significant downregulation of PLK2 in four different entities of human pulmonary fibrosis. Therefore, we characterized the pulmonary phenotype of PLK2 knockout (KO) mice. Isolated pulmonary PLK2 KO fibroblasts displayed a pronounced myofibroblast phenotype reflected by increased expression of αSMA, reduced proliferation rates and enhanced ERK1/2 and SMAD2/3 phosphorylation. In PLK2 KO, the expression of the fibrotic cytokines osteopontin and IL18 was elevated compared to controls. Histological analysis of PLK2 KO lungs revealed early stage remodeling in terms of alveolar wall thickening, increased alveolar collagen deposition and myofibroblast foci. Our results prompt further investigation of PLK2 function in pulmonary fibrosis and suggest that the PLK2 KO model displays a genetic predisposition towards pulmonary fibrosis, which could be leveraged in future research on this topic.

Systemic mesalazine treatment prevents spontaneous skin fibrosis in PLK2-deficient mice

“…Previous research of our group focused on PLK2 as a regulator of tissue homeostasis and fibrotic remodeling in the cardiovascular system (Kuenzel et al 2020 (Abstract); Kant et al 2021 ). In the present study, we characterize the cutaneous phenotype of the PLK2 KO mouse model.…”

“…Subsequently, the samples were embedded in paraffin, sectioned (5-µm layer thickness), and stained (hematoxylin/eosin (H&E) and picrosirius red) by the staff of the histology facility at the Center for Molecular and Cellular Bioengineering (CMCB), Dresden. The immunohistochemical staining was performed as described previously (Kant et al 2021 ). Fluorescence and brightfield images (for H&E and picrosirius red) were acquired with a Keyence BZ-X710 All-in-One Fluorescence Microscope (Keyence Corporation of America, USA) and a Zeiss Axio Observer Z1 microscope (Carl Zeiss AG, Germany).…”

“…for fibrillary αSMA was conducted as described previously (Poulet et al 2016;Hoffmann et al 2020;Kant et al 2021) to quantify myofibroblast differentiation. Therefore, 1*10 4 cells/well were seeded on glass coverslips in 24-well plates.…”

“…At this point, it remains the subject of future research to clarify whether activated resident tissue fibroblasts invade the subcutaneous layer or adipocytes transdifferentiate into myofibroblasts. Previous research on PLK2 KO identified spontaneous pro-fibrotic remodeling of the lungs accompanied by an increase in ERK1/2 phosphorylation and OPN overexpression (Kant et al 2021). Progression of interstitial lung disease is a major cause of death in patients suffering from systemic sclerosis (Volkmann and Fischer 2021).…”

“…We previously found that loss of polo-like kinase 2 (PLK2), a serine-threonine kinase regulating cell cycle progression, cell survival, and metabolism (Ma et al 2003;Matsumoto et al 2009;Mochizuki et al 2017) leads to ERK1/2-dependent overexpression of OPN and fibrotic remodeling of the heart and the lungs of PLK2-deficient mice (Kuenzel et al 2020 (Abstract); Kant et al 2021). Although there is growing experimental evidence that inhibition of OPN signaling yields pronounced antifibrotic effects (Wu et al 2012;Ramadan et al 2018), there is currently no clinically available drug targeting OPN specifically (Farrokhi et al 2018).…”