Deficiency of heat shock factor 4 promotes lens epithelial cell senescence through upregulating p21 expression.

Genetic mutations in heat shock factor 4 (Hsf4) is associated with both congenital and age-related cataracts. Hsf4 regulates lens development through its ability to both activate and inhibit transcription. Previous studies suggested Hsf4 is involved in modulating cellular senescence depending on p21 and p27 expression in MEF cells. Here, we found that Hsf4 acts as a suppressor of p21 expression and plays an anti-senescence role during lens development. Knocking out Hsf4 facilitated UVB-induced cellular senescence in mouse lens epithelial cells (mLECs). p21 was upregulated at both the mRNA and protein levels in HSF4 mLECs under control and UVB-treated conditions, and knockdown of p21 by siRNA alleviated UVB-induced cellular senescence. HSF4 directly bound to the p21 promoter and increased H3K27m3 levels at the p21 proximal promoter region by recruiting the methyltransferase EZH2. In animal models, p21 was gradually upregulated in wild-type mouse lenses with increasing age, while Hsf4 levels decreased. We generated a Hsf4 mutant mice line (Hsf4) which displayed obvious congenital cataract phenotype. The expression of p21 and senescence-associated cytokines were induced in the cataractous lenses of Hsf4 mice. H3K27m3 and EZH2 levels decreased in p21 promoters in the lenses of Hsf4 mice. The SA-β-Gal activities were positive in lens epithelia of aged Hsf4 zebrafish compared to wild-type lenses. p21 and senescence-associated cytokines levels were also upregulated in lenses of Hsf4 zebrafish. Accordingly, we propose that HSF4 plays a protective role in lens epithelial cells against cellular senescence during lens development and aging, partly by fine-tuning p21 expression.