Novel role of PKR in palmitate-induced Sirt1 inactivation and endothelial cell senescence

Abstract

Endothelial cell senescence is regarded as a vital characteristic of cardiovascular diseases. Elevated palmitate (PA) is an independent risk factor of cardiovascular diseases, but its role in endothelial cell senescence is currently unknown. During the course of studying the prosenescent role of PA, we discovered a key role of dsRNA-dependent protein kinase [protein kinase R (PKR)] in endothelial senescence. Exposure of human umbilical vein endothelial cells (HUVECs) to PA-induced cell senescence is characterized by increased levels of senescence-associated β-galactose glucosidase activity, excessive production of reactive oxygen species production, impaired cellular proliferation, and G phase arrest. This phenomenon is associated with an increase of PKR autophosphorylation and decreased activity of sirtuin 1 (Sirt1), a pivotal antisenescent factor. PKR inactivation by PKR siRNA or its phosphorylation inhibitor 2-aminopurine significantly attenuated PA-induced HUVEC senescence by reversing Sirt1 activity and its downstream signaling. Moreover, to study the regulatory mechanism between PKR and Sirt1, we found that PKR promotes JNK activation to inhibit Sirt1 activity and that this effect could be reversed by the JNK inhibitor SP600125. These findings provide evidence that PKR mediates PA-induced HUVEC senescence by inhibiting Sirt1 signaling. Our study provides novel insights into the actions and mechanisms of PKR in endothelial senescence. NEW & NOTEWORTHY This study first provides a novel observation that dsRNA-dependent protein kinase (PKR) mediates palmitate-induced sirtuin 1 inactivation and subsequent human umbilical vein endothelial cell senescence. Most importantly, these new findings will provide a potential therapeutic strategy to improve free fatty acid-induced endothelial senescence by targeting PKR in cardiovascular diseases.

Cellular senescence in cardiac diseases

“…When senescence-accelerated mice were fed a high-fat high-salt diet, endothelial cell senescence developed in cardiac tissues, and this coincided with the typical hemodynamic and structural changes of HFpEF [47]. Administration of palmitate, representing a metabolic stress, led to Sirt1 inactivation and increased senescent markers including p53, p16 Ink4a , and SA-b-gal in HUVECs [48]. Given that aged and/or obese population has higher prevalence for HFpEF, inhibition of endothelial cell senescence pathway may become a next generation therapy for this untreatable disorder.…”

PKR: A Kinase to Remember

“…A recent study has shown that PKR inhibition (either by siRNA for PKR or inhibition of its phosphorylation using 2-AP) can reverse palmitate-induced (an independent risk factor of cardiovascular diseases) senescence of HUVECs, by activating JNK. JNK activation results in inhibition of silent information regulator 1 (Sirt1), which serves as an anti-senescent factor (Li et al, 2018), by affecting downstream targets such as histones, transcription factors, and many other aging proteins, one of which is the tumor suppressor p53 (Volonte et al, 2015). Taken together, these studies point to PKR as an attractive target for the treatment of cardiovascular diseases.…”

The emerging role of cell senescence in atherosclerosis

“…The early stage is characterized by the presence of needle-like crystals in the arterial intima, as well as yellow-striped lesions (type I lesions) of different sizes, which are called the striate stage. It is well-known that HVECs senescence mediates endothelial damage, which occurs at the initial stage of atherosclerosis [4]. In turn, senescent HVECs lead to endothelial dysfunction, which increases the expression level of inflammatory cytokines and promotes the progression of atherosclerosis.…”