The Chemokine Platelet Factor-4 Variant (PF-4var)/CXCL4L1 Inhibits Diabetes-Induced Blood-Retinal Barrier Breakdown

Invest Ophthalmol Vis Sci. 2015 Feb 24;56(3):1956-64. doi: 10.1167/iovs.14-16144.


Purpose: To investigate the expression of platelet factor-4 variant (PF-4var/CXCL4L1) in epiretinal membranes from patients with proliferative diabetic retinopathy (PDR) and the role of PF-4var/CXCL4L1 in the regulation of blood-retinal barrier (BRB) breakdown in diabetic rat retinas and human retinal microvascular endothelial cells (HRMEC).

Methods: Rats were treated intravitreally with PF-4var/CXCL4L1 or the anti-vascular endothelial growth factor (VEGF) agent bevacizumab on the first day after diabetes induction. Blood-retinal barrier breakdown was assessed in vivo with fluorescein isothiocyanate (FITC)-conjugated dextran and in vitro in HRMEC by transendothelial electrical resistance and FITC-conjugated dextran cell permeability assay. Occludin, vascular endothelial (VE)-cadherin, hypoxia-inducible factor (HIF)-1α, VEGF, tumor necrosis factor (TNF)-α, receptor for advanced glycation end products (RAGE), caspase-3 levels, and generation of reactive oxygen species (ROS) were assessed by Western blot, enzyme-linked immunosorbent assays, or spectrophotometry.

Results: In epiretinal membranes, vascular endothelial cells and stromal cells expressed PF-4var/CXCL4L1. In vitro, HRMEC produced PF-4var/CXCL4L1 after stimulation with a combination of interleukin (IL)-1β and TNF-α, and PF-4var/CXCL4L1 inhibited VEGF-mediated hyperpermeability in HRMEC. In rats, PF-4var/CXCL4L1 was as potent as bevacizumab in attenuating diabetes-induced BRB breakdown. This effect was associated with upregulation of occludin and VE-cadherin and downregulation of HIF-1α, VEGF, TNF-α, RAGE, and caspase-3, whereas ROS generation was not altered.

Conclusions: Our findings suggest that increasing the intraocular PF-4var/CXCL4L1 levels early after the onset of diabetes protects against diabetes-induced BRB breakdown.

Keywords: blood-retinal barrier; diabetic retinopathy; platelet factor-4 variant (PF-4var CXCL4L1).

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Biomarkers / metabolism
  • Blood-Retinal Barrier / drug effects*
  • Blood-Retinal Barrier / physiology
  • Caspase 3 / metabolism
  • Cells, Cultured
  • Diabetes Mellitus, Experimental / complications*
  • Diabetic Retinopathy / drug therapy*
  • Diabetic Retinopathy / metabolism
  • Endothelial Cells / metabolism
  • Epiretinal Membrane / metabolism*
  • Humans
  • Male
  • Platelet Factor 4 / metabolism
  • Platelet Factor 4 / physiology
  • Platelet Factor 4 / therapeutic use*
  • Rats
  • Reactive Oxygen Species / metabolism
  • Vascular Endothelial Growth Factor A / metabolism
  • Vascular Endothelial Growth Factor A / pharmacology


  • Biomarkers
  • PF4V1 protein, human
  • Reactive Oxygen Species
  • Vascular Endothelial Growth Factor A
  • Platelet Factor 4
  • Caspase 3