Immune activation in retinal aging: a gene expression study.
OBJECTIVE
To investigate changes in gene expression during aging of the retina in the mouse.


METHODS
Total RNA was extracted from the neuroretina of young (3-month-old) and old (20-month-old) mice and processed for microarray analysis. Age-related, differentially expressed genes were assessed by the empiric Bayes shrinkage-moderated t-statistics


METHODS
Statistical significance was based on dual criteria of a ratio of change in gene expression >2 and a P < 0.01. Differential expression in 11 selected genes was further verified by real-time PCR. Functional pathways involved in retinal aging were analyzed by an online software package (DAVID-2008) in differentially expressed gene lists. Age-related changes in differential expression in the identified retinal molecular pathways were further confirmed by immunohistochemical staining of retinal flat mounts and retinal cryosections.


RESULTS
With aging of the retina, 298 genes were upregulated and 137 genes were downregulated. Functional annotation showed that genes linked to immune responses (Ir genes) and to tissue stress/injury responses (TS/I genes) were most likely to be modified by aging. The Ir genes affected included those regulating leukocyte activation, chemotaxis, endocytosis, complement activation, phagocytosis, and myeloid cell differentiation, most of which were upregulated, with only a few downregulated. Increased microglial and complement activation in the aging retina was further confirmed by confocal microscopy of retinal tissues. The most strongly upregulated gene was the calcitonin receptor (Calcr; >40-fold in old versus young mice).


CONCLUSIONS
The results suggest that retinal aging is accompanied by activation of gene sets, which are involved in local inflammatory responses. A modified form of low-grade chronic inflammation (para-inflammation) characterizes these aging changes and involves mainly the innate immune system. The marked upregulation of Calcr in aging mice most likely reflects this chronic inflammatory/stress response, since calcitonin is a known systemic biomarker of inflammation/sepsis.
Chen
Mei
M
Centre for Vision and Vascular Science, School of Medicine, Dentistry, and Biomedical Sciences, Queen's University Belfast, Belfast, Northern Ireland, United Kingdom.
Muckersie
Elizabeth
E
Forrester
John V
JV
Xu
Heping
H
D000375:Aging / Q000502:physiology*; D000818:Animals; D005136:Eye Proteins / Q000235:genetics; D019084:Fluorescent Antibody Technique, Indirect; D015870:Gene Expression / Q000502:physiology*; D005802:Genes, MHC Class II / Q000502:physiology*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018613:Microscopy, Confocal; D020411:Oligonucleotide Array Sequence Analysis; D012313:RNA / Q000235:genetics; D012160:Retina / Q000502:physiology*; D020133:Reverse Transcriptase Polymerase Chain Reaction
D005136:Eye Proteins; D012313:RNA