HSF4 regulates lens fiber cell differentiation by activating p53 and its downstream regulators

Meng Gao,David Wan-Cheng Li,Fei Liu,Shengjie Liao,Ling Wang,Xiliang Liu,Yuwen Huang,Tinsae Assefa Yimer,Shanshan Han,Lifang Yang,Zhaojing Lu,Mugen Liu,Xuebin Hu,Shanshan Yu,Zhen Qu,Zhaohui Tang,Mi Huang

doi:10.1038/cddis.2017.478

Abstract

Cataract refers to opacities of the lens that impede the passage of light. Mutations in heat shock transcription factor 4 (HSF4) have been associated with cataract; however, the mechanisms regarding how mutations in HSF4 cause cataract are still obscure. In this study, we generated an hsf4 knockout zebrafish model using TALEN technology. The mutant zebrafish developed an early-onset cataract with multiple developmental defects in lens. The epithelial cells of the lens were overproliferated, resulting in the overabundance of lens fiber cells in hsf4null zebrafish lens. Consequently, the arrangement of the lens fiber cells became more disordered and irregular with age. More importantly, the terminal differentiation of the lens fiber cell was interrupted as the organelles cannot be cleaved in due time. In the cultured human lens epithelial cells, HSF4 could stabilize and retain p53 in the nucleus to activate its target genes such as fas cell surface death receptor (Fas) and Bcl-2-associated X apoptosis regulator (Bax). In the hsf4null fish, both p53 and activated-caspase3 were significantly decreased. Combined with the finding that the denucleation defect could be partially rescued through microinjection of p53, fas and bax mRNA into the mutant embryos, we directly proved that HSF4 promotes lens fiber cell differentiation by activating p53 and its downstream regulators. The data we presented suggest that apoptosis-related genes are involved in the lens fiber cell differentiation. Our finding that HSF4 functions in the upstream to activate these genes highlighted the new regulatory modes of HSF4 in the terminal differentiation of lens fiber cell.

Highlights

Cataract is a major cause of adult blindness and congenital cataract is a major cause of childhood blindness.[1]
By constructing and analyzing the hsf4null zebrafish, we demonstrated the following: (1) hsf4null zebrafish develops an early-onset cataract and the pathologic condition remained with age; (2) the overproliferation of the lens epithelial cells contributes to excessive accumulation of the lens fiber cells, which interrupt lens normal arrangement pattern and lead to cataractogenesis; (3) at the cellular level, the denucleation of the primary fiber cell is much delayed in hsf4null lens, and this becomes even more severe in the differentiation progress of secondary fiber cells
Both nuclei and other cellular organelles including mitochondria, endosome and lysosome cannot be disintegrated. This is another reason for cataractogenesis; (4) at the molecular level, by stabilizing p53, HSF4 can regulate both extrinsic and intrinsic apoptotic pathways to mediate its control of lens differentiation

Summary

Introduction

Cataract is a major cause of adult blindness and congenital cataract is a major cause of childhood blindness.[1]. The HSF4 p.Arg116His mutation and the Hsf4(exon1)-DBD-EGFP hybrid gene transgenic mouse models have been constructed. Both models developed postnatal lamellar cataract, which is similar to the phenotype caused by the mutations in the DBD of human HSF4 gene.[17,18] These transgenic mice provide excellent models to study the lamellar cataract. Together, these studies revealed important functional aspects of the HSF4 gene. Recent studies demonstrated that lens differentiation is regulated by the same set of regulators responsible for the control of apoptosis.[19,20] These regulators include the tumor suppressor p53,21–28 Bcl-2 family

Methods

Results

Conclusion