Exacerbation of retinal degeneration in the absence of alpha crystallins in an in vivo model of chemically induced hypoxia

Abstract

This study evaluated the role of crystallins in retinal degeneration induced by chemical hypoxia. Wild type, αA-crystallin (−/−), and αB-crystallin (−/−) mice received intravitreal injection of 12 nmol (low dose), 33 nmol (intermediate dose) or 60 nmol (high dose) cobalt chloride (CoCl 2 ). Hematoxylin and eosin and TdT-mediated dUTP nick-end labeling (TUNEL) stains were performed after 24 hours, 96 hours, and 1 week post-injection, while immunofluorescent stains for αA-and αB-crystallin were performed 1 week post-injection. The in vitro effects of CoCl 2 on αB-crystallin expression in ARPE-19 cells were determined by real time RT-PCR, Western blot, and confocal microscopy and studies evaluating subcellular distribution of αB-crystallin in the mitochondria and cytosol were also performed. Histologic studies revealed progressive retinal degeneration with CoCl 2 injection in wild type mice. Retinas of CoCl 2 injected mice showed transient increased expression of HIF-1α which was maximal 24 hours after injection. Intermediate dose CoCl 2 injection was associated with increased retinal immunofluorescence for both αA-and αB-crystallin; however, after high dose injection, increased retinal degeneration was associated with decreased levels of crystallin expression. Injection of CoCl 2 at either intermediate or high dose in αA-crystallin (−/−) and αB-crystallin (−/−) mice resulted in much more severe retinal degeneration compared to wild type eyes. A decrease in ARPE-19 total and cytosolic αB-crystallin expression with increasing CoCl2 treatment and an increase in mitochondrial αB-crystallin were found. We conclude that lack of α-crystallins accentuates retinal degeneration in chemically-induced hypoxia in vivo.

Antiapoptotic Properties of α-Crystallin–Derived Peptide Chaperones and Characterization of Their Uptake Transporters in Human RPE Cells

“…[3][4][5]9,10,[26][27][28][29][30] Overexpression of aB- crystallin was found to offer protection while silencing rendered cells susceptible to apoptosis from oxidative injury. Signaling mechanisms of cellular protection varied depending on the imposed stress stimuli.…”

“…2 Both a-crystallins are expressed in RPE cells and in the retina; higher expression of aBcrystallin was found in the RPE while aA-crystallin was found mostly in photoreceptors and astroglial and Müller cells. 3,4 Furthermore, aB-crystallin was shown to be upregulated with several stress stimuli and to translocate to nuclei and mitochondrial compartments of RPE cells. 3,5 Microarray and proteomic analysis and histological studies have revealed that a-crystallin accumulates in drusen.…”

Methionine sulfoxide reductase A: Structure, function and role in ocular pathology

“…α-crystallins are major proteins of the small heat shock protein family and are expressed in several tissues [66][67][68] . α-crystallins have been studied extensively in the lens for their chaperone function, but α-crystallins are now generally understood to have additional non-lens roles [18][19][20][21]69,70] . In addition to being a molecular chaperone, α-crystallin functions in cell death inhibition, neuroprotection, proteosomal interactions, and regulation of angiogenesis [18][19][20][21]70,71] .…”

“…To counteract ROS damage, organisms have evolved multiple defense systems, including low molecular weight compounds and antioxidant enzymes that protect against oxidative stress. The antioxidant system includes glutathione peroxidase [6,7] , superoxide dismutase [8,9] , catalase [10,11] , thioredoxin reductase (TR) [12] , methionine sulfoxide reductase (Msr) [13][14][15][16][17] and several other proteins, including but not limited to small heat shock proteins, particularly α-crystallins [18][19][20][21] . Msrs are prominent among these antioxidant enzymes because of their roles as repair enzymes and indirect scavengers of ROS [4,22] .…”

The mitochondria-targeted antioxidant SkQ1 restoresαB-crystallin expression and protects against AMD-like retinopathy in OXYS rats

“…12 An increase of a-crystallin expression is a normal response to stressors. [27][28][29] At the same time, chronic stress can downregulate aB-crystallin, and this change could promote degenerative # Significant differences between untreated OXYS and Wistar rats (P < 0.05); *a significant effect of treatment with SkQ1 (P < 0.05). Confocal immunofluorescent images depict aB-crystallin (red signal) detected within the retina and RPE in OXYS rats (C) compared to disease-free Wistar (D) rats and (E) SkQ1-treated OXYS rats (250 nmol/kg per day from 1.5 to 4 months of age).…”