Abstract
Purpose :
Retinopathy of prematurity (ROP) is the leading cause of acquired visual impairment in children and may be impacted by inflammation. Lipopolysaccharide (LPS) induced systemic inflammation (SI) in mouse pups is known to reduce retinal vascular area and density. Published data from our lab shows that levels of Surfactant protein A (SP-A) are low during the first week of life in mouse pups and that lack of SP-A leads to decreased neovascularization in the OIR model. We therefore hypothesize that lack of SP-A reduces retinal vascularization and compare the impact of absence of SP-A to SI induced by LPS.
Methods :
We induced SI in wild type (C57BL6/J, WT) and SP-A-/- mice at P4, by intraperitoneal injection of LPS (1 mg/kg), compared to mice injected with saline solution as control (NS). Retinas were dissected for flat mounting (FM) at P6, P8 and P10. Retinal blood vessels were visualized by immunohistochemistry (IHC) on FM’s with antibodies against endothelial CD31. Vascular area, vascular density and the length of stalk and number of tip cells at the vascular front were quantified using image analysis software. VEGF gene expression was evaluated by RT-PCR.
Results :
Significant differences were seen at P6. Vascular area was significantly reduced in SP-A-/--LPS mice vs. WT-NS (56 % vs 73 %), in SP-A-/--LPS vs. SP-A-/--NS (56 % vs 64 %) and in SP-A-/--NS vs. WT-NS (64 % vs 73 %). Vascular density was significantly decreased by 4 % in SPA-/--LPS mice vs the three other groups (p<0.001). Length of stalk cells was 1.6-fold greater in SPA-/- vs. WT while the number of tip cells was 2-fold lower in LPS vs. NS. In the retinas from LPS injected mice, VEGF expression was lowered by 10-fold.
Conclusions :
Both, SI and lack of SP-A decrease retinal vascular area and density independently of each other and compound their effects when both insults occur simultaneously. However, absence of SP-A has 1.5-fold stronger effect on the decrease of vascular area. Furthermore, while LPS leads to a reduction in VEGF levels as well as the total number of tip cells on the vascular front, the deficiency of SP-A-/- leads to elongation of stalk cells. This is significant because premature infants who have low levels of SP-A with an additional insult of SI or sepsis are at greater risk of impaired retinal vascular development. We are working to determine the underlying mechanisms.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.