Pharmacological Activation of Autophagy Restores Cellular Homeostasis in Ultraviolet-(B)-Induced Skin Photodamage.

Malik Ahmad Tanveer,Lone Ahmad Nazir,Sheikh Abdullah Tasduq,Gupta Divya,Sharma Rai Raghu,Sheikh Ahmad Umar,Sajida Archoo,Naikoo Hussain Shahid

doi:10.3389/fonc.2021.726066

Abstract

Ultraviolet (UV) exposure to the skin causes photo-damage and acts as the primary etiological agent in photo-carcinogenesis. UV-B exposure induces cellular damage and is the major factor challenging skin homeostasis. Autophagy allows the fundamental adaptation of cells to metabolic and oxidative stress. Cellular dysfunction has been observed in aged tissues and in toxic insults to cells undergoing stress. Conversely, promising anti-aging strategies aimed at inhibiting the mTOR pathway have been found to significantly improve the aging-related disorders. Recently, autophagy has been found to positively regulate skin homeostasis by enhancing DNA damage recognition. Here, we investigated the geno-protective roles of autophagy in UV-B-exposed primary human dermal fibroblasts (HDFs). We found that UV-B irradiation to HDFs impairs the autophagy response in a time- and intensity-independent manner. However, improving autophagy levels in HDFs with pharmacological activators regulates the UV-B-induced cellular stress by decreasing the induction of DNA photo-adducts, promoting the DNA repair process, alleviating oxidative and ER stress responses, and regulating the expression levels of key cell cycle regulatory proteins. Autophagy also prevents HDFs from UV-B-induced nuclear damage as is evident in TUNEL assay and Acridine Orange/Ethidium Bromide co-staining. Salubrinal (an eIF2α phosphatase inhibitor) relieves ER stress response in cells and also significantly alleviates DNA damage and promotes the repair process in UV-B-exposed HDFs. P62-silenced HDFs show enhanced DNA damage response and also disturb the tumor suppressor PTEN/pAKT signaling axis in UV-B-exposed HDFs whereas Atg7-silenced HDFs reveal an unexpected consequence by decreasing the UV-B-induced DNA damage. Taken together, these results suggest that interventional autophagy offers significant protection against UV-B radiation-induced photo-damage and holds great promise in devising it as a suitable therapeutic strategy against skin pathological disorders.

Highlights

Skin being the external covering of the body protects internal organs from outside environmental insults including the adverse effects of ultraviolet (UV) irradiation [1]
UV-B exposure to human dermal fibroblasts (HDFs) increases the expression levels of LC3BII at 24 h but not at 3 and 6 h, downregulates P62 expression initially in an insignificant manner but not at 24 h, and increases the expression of BECN1 in an altered fashion, which increases immediately after UV-B exposure, but the expression is blocked in delayed post-exposure, which does not correspond to induction of autophagy response
We confirmed the induction of impaired autophagic flux response upon UV-B 30 mJ/cm2 exposure to HDFs through GFP-RFP-LC3B puncta assay in confocal microscopy depicting appreciable red puncta dots, indicative of autolysosomes compared to yellow puncta dots indicative of autophagosomes in Rapamycin- and Salubrinaltreated cells showing enhanced autophagy flux upon UV-B exposure to HDFs compared to those exposed only to UV-B

Summary

Introduction

Skin being the external covering of the body protects internal organs from outside environmental insults including the adverse effects of ultraviolet (UV) irradiation [1]. We have reported in another study that the natural antioxidant bio-active molecule Glycyrrhizic acid (GA) alleviates oxidative stress-induced DNA damage response (DDR) by improving cellular autophagy signaling in UV-B-irradiated primary HDFs [19]. Despite these preliminary findings, the role of autophagy in UV-B-induced photo-damage response is unclear and warrants further studies to unravel the facts. The above findings suggest that pharmacological activation of autophagy significantly alleviates the DNA damage and promotes the DNA repair process in UV-B-exposed HDFs and is critical in restoring cellular homeostasis These results suggest that interventional autophagy holds great promise to be devised as a suitable therapeutic strategy against radiation-induced skin photodamage disorders

Methods

Results

Discussion

Conclusion