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CFH and HTRA1 exhibit antagonistic effect on inhibiting oxidized phospholipids uptake in human retinal pigment epithelial cells

  • Author(s): Lin, Victor
  • Advisor(s): Shaw, Peter;
  • Feng, Gen-Sheng
  • et al.

Age-related macular degeneration (AMD) is a major cause of central vision loss among the elderly. Genome-wide association studies (GWAS) have implicated polymorphisms in complement factor H (CFH) and high-temperature requirement A1 (HTRA1) in progression to advanced AMD. The complement factor H plays a key regulator role in complement system of the innate immune defense. CFH is also found to have high affinity binding with oxidized phospholipids (oxPLs), which shields oxPLs from inducing inflammation in the eye. On the other hand, the HTRA1 is a serine protease that is identified to be an extracellular matrix homeostasis regulator and TGF-β1 pathway inhibitor. Despite the extensive studies on the two proteins’ respective properties and involved pathways, the mechanism between the genetic risk factors and AMD disease pathology remains to be explored. My research project investigates the cellular interactions and molecular mechanisms of CFH and HTRA1 in elevated oxidative stress environment. In this study, recombinant CFH and HTRA1 variants were produced for the experiments. The inhibitory effect of CFH and HTRA1 in modulating the uptake of oxidized low-density lipoprotein (oxLDL) into the retinal pigment epithelium cells (RPE) is demonstrated by Oil Red O staining. The CFH risk variant was identified to exhibit competitive binding against HTRA1 interaction with lipoproteins via competitive ELISA. Furthermore, CD36 mRNA expression is found to be significantly heightened with the administration of HTRA1 or oxidative stress. However, the CD36 protein level analysis via immunocytochemistry and western blot demonstrates reduction of CD36 protein expression by proteolytic active HTRA1. We also found that CD36 protein expression is either preserved or enhanced with the addition of CFH variants, which we speculate to protect CD36 against proteolytic cleavage by HTRA1. This preliminary evidence suggests that CFH and HTRA1 have an antagonistic effect on inhibiting oxidized phospholipids uptake in RPE cells. This finding provides a new aspect of complement independent role of CFH in lipid metabolism which may be explored as a therapeutic treatment to AMD.

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