Lipocalin-2 Restores Soluble Guanylyl Cyclase-Dependent Dilation of the Afferent Arteriole After Renal Transplantation or Ex Vivo Hypoxia/Reoxygenation in Mice

Abstract

Aim: Dilatory microvascular function is impaired in ischemia/reperfusion injury in the kidney. Nitric oxide independent activators of soluble guanylyl cyclase (sGC) provide renal protection by dilating microvessels and preserving perfusion, but their efficacy declines after severe hypoxia. This study explores whether lipocalin-2 (Lcn2), a key iron-transporting protein, can restore the sGC-mediated dilation in mouse afferent arterioles (AAs) after hypoxia/reoxygenation (H/R) and kidney transplantation.

Methods: Dilation of isolated, angiotensin II (Ang II) pre-constricted, AAs was induced by application of sGC activator cinaciguat after pre-constriction with Ang II following H/R (H: 30 min, R: 10 min ± holo-rLcn2, apo-rLcn2, deferoxamine) and syngeneic kidney transplantation (cold ischemia: 30 min or 5.5 h, reperfusion: 20 h ± holo-rLcn2) in C57BL/6 mice. To corroborate the dilatory function at the organ level, vascular relaxation was assessed using an isolated mouse kidney perfusion system.

Results: Dilation of AAs was impaired following H/R. Pretreatment with holo-rLcn2 (iron-bound) preserved dilation, whereas apo-rLcn2 (iron-free) had no effect. The reversal of holo-rLcn2's effect by deferoxamine confirmed the role of iron. AAs from kidney transplants showed reduced dilation compared to sham-operated controls, with greater impairment following prolonged ischemia. Treatment with holo-rLcn2 significantly improved dilatory function after extended cold ischemia (5.5 h), restoring it to levels seen with shorter ischemia (30 min). Ex vivo perfusion of the isolated mouse kidney with holo-rLcn2 enhanced cinaciguat-induced vascular relaxation, confirming its beneficial effect at the organ level.

Conclusion: This study identifies a novel role for holo-rLcn2 in preserving renal vascular function post-H/R and kidney transplantation, apparently by upholding iron levels in vascular cells.

Keywords: Lipocalin‐2; hypoxia/reoxygenation; microvascular function; mouse kidney transplantation.