Parainflammation associated with advanced glycation endproduct stimulation of RPE in vitro: Implications for age-related degenerative diseases of the eye

Abstract

Age related macular degeneration (AMD) is one of the leading causes of blindness in Western society. A hallmark of early stage AMD are drusen, extracellular deposits that accumulate in the outer retina. Advanced glycation endproducts (AGE) accumulate with aging and are linked to several age-related diseases such as Alzheimer's disease, osteoarthritis, atherosclerosis and AMD. AGE deposits are found in drusen and in Bruch's membrane of the eye and several studies have suggested its role in promoting oxidative stress, apoptosis and lipofuscin accumulation. Recently, complement activation and chronic inflammation have been implicated in the pathogenesis of AMD. While AGEs have been shown to promote inflammation in other diseases, whether it plays a similar role in AMD is not known. This study investigates the effects of AGE stimulation on pro- and anti-inflammatory pathways in primary culture of human retinal pigment epithelial cells (RPE). Differential gene expression studies revealed a total of 41 up- and 18 down-regulated RPE genes in response to AGE stimulation. These genes fell into three categories as assessed by gene set enrichment analysis (GSEA). The main categories were inflammation (interferon-induced, immune response) and proteasome degradation, followed by caspase signaling. Using suspension array technology, protein levels of secreted cytokines and growth factors were also examined. Anti-inflammatory cytokines including IL10, IL1ra and IL9 were all overexpressed. Pro-inflammatory cytokines including IL4, IL15 and IFN-γ were overexpressed, while other pro-inflammatory cytokines including IL8, MCP1, IP10 were underexpressed after AGE stimulation, suggesting a para-inflammation state of the RPE under these conditions. Levels of mRNA of chemokine, CXCL11, and viperin, RSAD2, were up-regulated and may play a role in driving the inflammatory response via the NF-kB and JAK-STAT pathways. CXCL11 was strongly immunoreactive and associated with drusen in the AMD eye. The pathways and novel genes identified here highlight inflammation as a key response to AGE stimulation in primary culture of human RPE, and identify chemokine CXCL11 as putative novel agent associated with the pathogenesis of AMD.

Cellular responses following retinal injuries and therapeutic approaches for neurodegenerative diseases

“…Likewise, a higher accumulation of AGEs and an acceleration of the appearance of age-related retinal lesions have been demonstrated in the retinas of animal models consuming high glycemic index foods, thus suggesting a relationship with the disease etiology (Chiu et al, 2011;Handa et al, 1999;Uchiki et al, 2012;Weikel et al, 2012). When RPE cells are exposed to AGEs, a para-inflammation state may develop in conjunction with an adaptive response from RPE cells, but when the exposure becomes chronic, it is possible that the stresses overpower the adaptive mechanisms of RPE cells, resulting in dysfunction and death (Lin et al, 2013).…”

Oxidative stress in dry age-related macular degeneration and exfoliation syndrome

“…In AMD-affected eyes, the mtDNA recovered from macular RPE cells has more damage than that of age-matched controls, and mtDNA damage is enriched in the RPE cells of the macular region as compared to the peripheral retina 33,36 . Moreover, the ROS-associated mtDNA damage parallels disease severity and is positively correlated with progression of AMD, while repair capacity is negatively correlated 17,33 . This increase in mtDNA damage correlates with decreases in 8-oxoguanine glycosylase, a marker of mtDNA repair capacity 17 , and this damage is distributed evenly in the mtDNA genome, as measured by long-PCR 37 .…”

“…Moreover, the ROS-associated mtDNA damage parallels disease severity and is positively correlated with progression of AMD, while repair capacity is negatively correlated 17,33 . This increase in mtDNA damage correlates with decreases in 8-oxoguanine glycosylase, a marker of mtDNA repair capacity 17 , and this damage is distributed evenly in the mtDNA genome, as measured by long-PCR 37 . Abnormal regulation of several mitochondrial proteins, including ATP synthase, cytochome C oxidase and mitochondrial heat shock protein 70, is noted in AMD-affected retinas 36 .…”

Vinpocetine inhibits amyloid-beta induced activation of NF-κB, NLRP3 inflammasome and cytokine production in retinal pigment epithelial cells

“…Systemic vinpocetine, a well-tolerated antiinflammatory agent, inhibited NF-kB activation in the RPE as well as NF-κB-dependent processes including inflammasome activation and cytokine production. NF-κB is a key upstream regulator of the inflammatory pathways that is not only activated by Aβ but is likely involved in the RPE's response to other pathological, age-related stimuli and drusen components such as carboxyethylpyrrole (CEP) and advanced glycation endproduct (AGE) (Lin et al, 2013). NF-κB inhibition may be a useful approach to control the chronic inflammation that is believed to drive the degenerative processes in early AMD, but more studies are needed to ascertain other cellular changes that may be affected by long-term inhibition of this important transcription factor.…”

“…Although the majority of disease burden from vision loss derives from the advanced forms of AMD, it is known that drusen accumulation starts decades earlier and may promote a chronic state of parainflammation in the outer retina (Hageman et al, 2001;Lin et al, 2013;Xu et al, 2009). Therefore, effective early AMD intervention requires the understanding of these inflammatory events and the identification of valid cellular targets.…”