Anti-senescence properties of the flavone Silymarin in the diabetic retina involve direct inhibition of the histone deacetylase 6 (HDAC6)

Abstract

Purpose : We have previously shown that in the diabetic retina histone deacetylase 6 (HDAC6) is one of the initiating factors promoting stress-induced premature senescence (SIPS) in the retinal vasculature. This is a key pathogenic process involved in the onset and progression of diabetic retinal microangiopathy and diabetic retinopathy (DR). Anti-aging and senolytic drugs are thought to be beneficial for neurodegeneration and cardiovascular disease including diabetes. Silymarin (SIL) is a flavone that has been shown to halt senescence in a number of cell types including endothelial cells. Here we have investigated the effects of SIL on retinal vascular SIPS in an experimental model of DR also determining its inhibitory ability towards HDAC6.

Methods : Morphological and biochemical analyses were performed comparing streptozotocin-induced diabetic rats (STZ) with age-matched normoglycemic rats (control) and with STZ-rats that received SIL (200 mg/Kg/day p.o.) starting 2 weeks after the onset of hyperglycemia and continued for all the duration of diabetes (8 weeks). SIPS was shown by immunostaining for S-A-beta GAL and by immunoblotting for p16ink4a and p21waf. HDAC6 expression and activity were measured by immunoblotting and fluorescence enzymatic assay, respectively. Docking studies were done to elucidate at molecular level SIL and HDAC6 interaction.

Results : Our analyses showed that SIL preserved retina cells survival while down-regulating the expression of pro-inflammatory and pro-oxidant factors. SIL also reduced the expression of senescence markers and downregulated the expression and activity of HDAC6. Docking studies-based predictions revealed SIL potential interaction with both the catalytic and zinc-finger ubiquitin-binding domains of HDAC6 demonstrating strong inhibitory activity of SIL towards this deacetylase.

Conclusions : Overall, our studies demonstrate SIL beneficial effects in the diabetic retina by preventing diabetes-induced retinal vascular SISP through its inhibitory activity towards HDAC6. These results also warrant further studies to assess SIL senolytic activity and set the stage to clinical studies evaluating the use of this flavone as potential adjuvant therapy for DR.

This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.