Objectives:
Many of the clinical complications associated with sickle cell disease (SCD), such as stroke, pain crises, proliferative retinopathy, renal and heart failure, can be attributed to repeated bouts of vascular insufficiency, yet the detailed mechanisms of vascular repair following injury are largely unknown in SCD. Given our previous work showing the importance of reactive oxygen species in neovascularization, we aimed to delineate the immune mechanisms of oxidative stress during vascular repair in a humanized sickle cell mouse model (SS) in comparison to wildtype (AA).
Methods:
We performed limb ischemia (HLI) in mice by ligation of the femoral artery to evaluate vascular dysfunction in sickle cell mice. Vascular recovery was ascertained using weekly LASER Doppler perfusion imaging (LDPI) for 28 days. Voluntary running wheel test was used to determine spontaneous motor function recovery.
Results:
There was significant diminution in functional collateral vessel formation in SS mice following HLI as evaluated by LDPI (76 ±13 % recovery in AA vs 34±10 % recovery in SS by day 28, p < 0.001 n=8 per group). This was characterized by dysfunctional Moyamoya-like sprouting vessels with impaired spontaneous motor function recovery in SS. Specifically, AA mice recovered 98% motor function by day 28 following HLI, vs 36% in SS mice, p < 0.001. The phenotype was associated with persistent neutrophils in the hind limb muscle of SS mice up to 28 days, a time point by which all neutrophils were cleared in AA mice. Consequently, there was a 2.45 fold increased production of hydrogen peroxide in SS mice ischemic hind limbs at day 28, compared to AA mice (p< 0.05). Importantly,
in vivo
depletion of neutrophils improved functional collateral vessel formation in the SS mice.
Conclusions:
Our data suggest that neutrophil-mediated excessive inflammation and oxidative stress drive dysfunctional collateral vessel formation in SS mice following ischemic injury. Targeting neutrophils may improve vascular dysfunction in SS disease.
Impaired Collateral Vessel Formation in Sickle Cell Disease