Down-regulation of aryl hydrocarbon receptor intensifies carcinogen-induced retinal lesion via SOCS3-STAT3 signaling

The aryl hydrocarbon receptor (AHR) is a ligand-activated receptor that regulates the metabolism of several xenobiotics and participates in ocular inflammation. Although severe inflammation is a major risk of retinal damage, the underlying mechanism is not well established. In this study, to elucidate how AHR mediates inflammation homeostasis, we hypothesized that AHR expression may diminish during long-term exposure to benzo [a] pyrene (B [a]P), a carcinogen in cigarette smoke. The blockage of AHR function considerably impaired suppressor of cytokine signaling 3 (SOCS3) negative feedback regulation and upregulated B [a]P-induced pro-inflammation. Signal transducer and activator of transcription 3 (STAT3) was activated by B [a] P due to AHR dysfunction in human adult retinal pigment epithelial cells (ARPE-19). The STAT3-inducible element revealed higher activity in AHR knockout cells with B [a] P treatment, but not in wild type ARPE-19 cells. Moreover, AHR dysfunction led to STAT3 hypo-ubiquitination and changed the STAT3–SOCS3 interaction. Increased STAT3–SOCS3 complex during AHR dysfunction by B [a] P was suppressed by nifuroxazide in ARPE-19 cells. Furthermore, the in vivo results showed that STAT3 inhibition during AHR impairment by long-term B [a] P exposure preserved the retina thickness and reversed the visual function in male C57Bl/6 mice. Overall, long-term B [a] P exposure may attenuate AHR function, dysregulating the homeostasis of the SOCS3–STAT3 axis with intensive STAT3 activation. This finding is significant given that the disintegration of the AHR–SOCS3 axis is a sensitive factor involved in AMD-like lesion development in the retina, revealing that the low AHR level may be associated with cigarette smoking or xenobiotics exposure, causing retina inflammation and damage.