Sirtinol Supresses Trophozoites Proliferation and Encystation of Acanthamoeba via Inhibition of Sirtuin Family Protein

Abstract

The encystation of Acanthamoeba leads to the development of metabolically inactive and dormant cysts from vegetative trophozoites under unfavorable conditions. These cysts are highly resistant to anti-Acanthamoeba drugs and biocides. Therefore, the inhibition of encystation would be more effective in treating Acanthamoeba infection. In our previous study, a sirtuin family protein—Acanthamoeba silent-information regulator 2-like protein (AcSir2)—was identified, and its expression was discovered to be critical for Acanthamoeba castellanii proliferation and encystation. In this study, to develop Acanthamoeba sirtuin inhibitors, we examine the effects of sirtinol, a sirtuin inhibitor, on trophozoite growth and encystation. Sirtinol inhibited A. castellanii trophozoites proliferation (IC50=61.24 μM). The encystation rate of cells treated with sirtinol significantly decreased to 39.8% (200 μM sirtinol) after 24 hr of incubation compared to controls. In AcSir2-overexpressing cells, the transcriptional level of cyst-specific cysteine protease (CSCP), an Acanthamoeba cysteine protease involved in the encysting process, was 11.6- and 88.6-fold higher at 48 and 72 hr after induction of encystation compared to control. However, sirtinol suppresses CSCP transcription, resulting that the undegraded organelles and large molecules remained in sirtinol-treated cells during encystation. These results indicated that sirtinol sufficiently inhibited trophozoite proliferation and encystation, and can be used to treat Acanthamoeba infections.

Biological characteristics and pathogenicity of Acanthamoeba

“…The same group also found that AcSir2 promotes encystation by increasing the expression of cyst-specific cysteine protease (CSCP). Sirtinol, another Sir2 inhibitor, suppresses CSCP transcription, suggesting that the undegraded organelles and large molecules remained in sirtinol-treated cells during encystation ( Joo et al, 2022 ). In Saccharomyces cerevisiae , SIR2 levels increase during calorie restriction ( Lin et al, 2000 ), and sirtuin overexpression is known to extend the lifespan by silencing HML and HMR loci and inhibiting the formation of extrachromosomal rDNA circles ( Sinclair and Guarente, 1997 ; Kaeberlein et al, 1999 ).…”