P38 MAPK Signaling in the Retina: Effects of Aging and Age-Related Macular Degeneration

Abstract

Age-related macular degeneration (AMD) is the leading cause of irreversible visual impairment worldwide. Age is the greatest risk factor for AMD but the underlying mechanism remains unascertained, resulting in a lack of effective therapies. Growing evidence shows that dysregulation of the p38 MAPK signaling pathway (SP) contributes to aging and neurodegenerative diseases; however, information about its alteration in the retina with age and during AMD development is limited. To assess the contribution of alterations in p38 MAPK signaling to AMD, we compared age-associated changes in p38 MAPK SP activity in the retina between Wistar rats (control) and OXYS rats, which develop AMD-like retinopathy spontaneously. We analyzed changes in the mRNA levels of genes of this SP in the retina (data of RNA-seq) and evaluated the phosphorylation/activation of key kinases using Western blotting at different stages of AMD-like pathology including the preclinical stage. p38 MAPK SP activity increased in the retinas of healthy Wistar rats with age. The manifestation and dramatic progression of AMD-like pathology in OXYS rats was accompanied by hyperphosphorylation of p38 MAPK and MK2 as key p38 MAPK SP kinases. Retinopathy progression co-occurred with the enhancement of p38 MAPK-dependent phosphorylation of CryaB at Ser59 in the retina.

Keywords: MAPK14; OXYS rat; age-related macular degeneration; aging; p38 MAPK; phosphorylation.

Figure 1

Age-related changes in the expression of genes of the p38 MAPK SP in the retina of Wistar and OXYS rats. Numbers of DEGs depending on age in Wistar and OXYS rats (a). DEGs of the p38 MAPK SP in Wistar (b) and OXYS (c) rats with age. Numbers of DEGs in 20-day-old and 3- and 18-month-old OXYS rats compared to age-matched Wistar rats (d). Differential expression means a comparison with the parental control strain (Wistar) (e). The data are highlighted in green for upregulation and in red for downregulation of genes.

Figure 2

Protein amounts of p38 MAPK, p-p38 MAPK, MK2, and p-MK2 in the retinas of Wistar rats and OXYS rats at the ages of 20 days and 3 and 18 months. Representative Western blot images of proteins p38 MAPK and p-p38 MAPK (a). Graphical presentation of p38 MAPK (b) and p-p38 MAPK (c) protein levels and the ratio of p-p38 MAPK to p38 MAPK (d); MK2 (e) and p-MK2 (f) protein amounts and the ratio of p-MK2 to MK2 (g). The protein amounts were normalized to GAPDH. The results of six independent experiments are presented. The data are shown as a median with an interquartile range (q1–q3). ^ Significant differences from a previous age within a strain; * significant differences between the strains at the same age (p < 0.05).

Figure 3

Protein amounts of CryaB and p-CryaB-S59 in the retinas of Wistar rats and OXYS rats at ages 20 days and 3 and 18 months. (a) Representative Western blot images of proteins. Graphical presentation of CryaB (b) and p-CryaB-S45 (c) protein levels, and of the ratio of p-CryaB-S59 to CryaB (d). The protein amounts were normalized to GAPDH. Results of six independent experiments are presented. The data are shown as a median (q1–q3). ^ Significant differences from a previous age within a strain; * significant differences between the strains at the same age (p < 0.05).