Heat shock cognate-70 gene expression declines during normal aging of the primate retina

Despite documented age-related changes in retinal function and histology, little is known about the pattern of gene expression during normal aging of the vertebrate retina. This study was undertaken to definitively characterize gene expression in the primate retina during aging.

Human retina cDNA library clones were arrayed at high density on nylon membranes and screened with mixed cDNA probes generated from young (4-year-old) and old (80-year-old) human retinae. Clones showing a more than twofold difference in intensity were rescreened by dot blot analysis with the same probes and with mixed cDNA probes generated from young (2-3 years) and old (27-35 years) rhesus monkeys. One clone identified by its differential (age-putative) signal, and age-related differential expression was used for analysis of Northern blot analysis of total retinal RNA from human donors (35 weeks to 94 years of age) and two rhesus monkeys (2 and 27 years of age). The identified clone was sequenced and compared with entries in the GenBank/EMBL databases. Western blot analysis was performed on protein isolated from the retina of human donors aged 4 to 64 years and rhesus monkeys aged 18 months and 35 years.

Approximately 1.6% of the 55,368 retina-expressed sequences examined show age-related changes between tissues from young and old donors. The mRNA level one clone, identical with heat shock cognate (HSC)70, was altered during normal retinal aging in primates. Regression analysis of Northern blot analysis signals from 23 human donors suggested that there may be a two- to threefold decrease in HSC70 mRNA levels in the human retina by the eighth decade of life. Western blot analysis also showed lower levels of the 70-kDa HSC protein in older tissues of both primates.

HSC70 mRNA levels apparently decline during normal aging of the primate retina. Because the heat shock 70 protein family may play important roles in ocular development and protection from various biologic and environmental stresses, decreased HSC70 levels in the retina during aging may contribute to the apparent increased susceptibility of the retina to age-acquired retinal disease.