Abstract
Purpose :
In normal adults, 97% of total red cell hemoglobin (Hb) is adult Hb (HbA). Elevated fetal Hb (HbF) levels post-infancy generally indicate underlying metabolic stress and tissue hypoxia. HbF binds oxygen with higher affinity than HbA; increased HbF production is regarded as a “rescue” attempt by the body to increase oxygen extraction and subsequent delivery to tissues under low oxygen conditions. Hb production by RPE brings new perspectives regarding the understanding of outer retinal oxygenation under normal conditions. In light of this discovery, the known high metabolic activity and consequent demand of photoreceptors for oxygen, here we evaluated whether HbF modulation confers benefit in retina under hypoxic conditions characteristic of aging and diabetes. Additionally, we investigated the underlying molecular mechanisms responsible.
Methods :
Mice engineered to produce human Hb were used in this study: abnormal Hb (HbSS)-producing mice to study the effects of HbF augmentation on chronic, low-grade hypoxia that occurs in aging and, normal Hb (HbAA)-producing mice ± STZ, to examine its effects on diabetes-induced hypoxia. Animals were treated ± the HbF-inducer monomethylfumarate (MMF; 15 mg/ml in drinking water). Retinal health/function was monitored by ERG, OCT, and routine histologic, RNA and protein analyses. MMF-induced alterations in gene/protein expression were evaluated also in ARPE-19 cells cultured ± MMF (100 μM) under normal, hyperglycemic (25 mM glucose) or hypoxic (100 μM CoCl2 or 1% oxygen) conditions.
Results :
Oral MMF-therapy increased γ-globin mRNA/HbF production systemically and in retina, reduced oxidative stress/inflammation, and preserved outer retinal morphology/function positively in chronically hypoxic retinas (HbSS and HbAA+STZ). MMF induced Nrf2 and downregulated Bcl11A, a repressor of γ-globin transcription and regulator of cell metabolism and senescence. siRNA studies demonstrated the effect on Bcl11A to be Nrf2-dependent.
Conclusions :
This study exposes novel potential links between factor that govern globin gene switching, redox status, metabolism and senescence and suggests that HbF-inducing therapies might afford multiple levels of benefit in hypoxic retina.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.