HIF-1: an age-dependent regulator of lens cell proliferation.
OBJECTIVE
The lens grows throughout life, and lens size is a major risk factor for nuclear and cortical cataracts. A previous study showed that the hypoxic environment around the lens suppressed lens growth in older rats. The present study was conducted to investigate the mechanism responsible for the age-dependent decline in lens cell proliferation.


METHODS
Transgenic mice expressing Cre recombinase in the lens were bred to mice containing floxed Hif1a alleles. Transgenic mice expressing oxygen insensitive forms of HIF-1alpha in lens epithelial cells were exposed to room air or 60% oxygen. Proliferation was measured by BrdU labeling and cell death by using the TUNEL assay. Morphology was assessed in histologic sections. HIF-1alpha and p27(KIP1) levels were determined by Western blot. The expression of HIF-regulated genes was assessed on microarrays.


RESULTS
Lenses lacking Hif1a degenerated, precluding study in older animals. Breathing 60% oxygen reduced HIF-1alpha levels and HIF-1-regulated transcripts in lens epithelial cells from young and older lenses. Overexpression of oxygen-insensitive HIF-1alpha had no effect on lens size, but suppressed increased proliferation in response to oxygen. Systemic injection of the iron chelator, 1,10-phenanthroline prevented the degradation of HIF-1alpha and reduced oxygen-induced proliferation. Increasing oxygen decreased levels of p27(KIP1) in the epithelial cells of older mice, which was prevented by expressing oxygen-insensitive forms of HIF-1alpha.


CONCLUSIONS
HIF-1alpha is present and HIF-1 is transcriptionally active throughout life, but suppresses growth only in older lenses. Maintaining elevated levels of p27(KIP1) in older lenses requires HIF-1. p27(KIP1) and other growth regulators may selectively suppress the proliferation of older lens epithelial cells.
Shui
Ying-Bo
YB
Department of Ophthalmology and Visual Sciences, Washington University, St Louis, Missouri 63110, USA.
Arbeit
Jeffrey M
JM
Johnson
Randall S
RS
Beebe
David C
DC
D000375:Aging / Q000378:metabolism*; D000483:Alleles; D000818:Animals; D017209:Apoptosis; D015153:Blotting, Western; D049109:Cell Proliferation; D003300:Copper; D003432:Cross-Linking Reagents; D005260:Female; D018507:Gene Expression Regulation, Developmental; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000096:biosynthesis / Q000187:drug effects / Q000235:genetics*; D020287:In Situ Nick-End Labeling; D007908:Lens, Crystalline / Q000166:cytology / Q000187:drug effects / Q000254:growth & development*; D051379:Mice; D008807:Mice, Inbred BALB C; D018345:Mice, Knockout; D046228:Microarray Analysis; D010100:Oxygen / Q000494:pharmacology; D010618:Phenanthrolines / Q000494:pharmacology; D012313:RNA / Q000235:genetics*
D003432:Cross-Linking Reagents; C497443:Hif1a protein, mouse; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D010618:Phenanthrolines; D012313:RNA; D003300:Copper; D010100:Oxygen; C025205:1,10-phenanthroline