Involvement of hyaluronan in the pathophysiology of renal ischemia-reperfusion injury

Abstract

Acute kidney injury (AKI) is a clinical syndrome that still remains associated with high morbidity and mortality rates in humans and can lea
d to the development of end-stage renal disease. One of the major causes of AKI is ischemia-reperfusion injury (IRI), a pathological process that often occurs in renal allografts and after major vascular surgery. IRI results from a combination of events including cellular hypoxia, tubular and endothelial injuries as well as inflammatory processes. IRI may be followed by a repair process but, if incomplete, it can lead to permanent damage and chronic kidney disease. During IRI, hyaluronan (HA), a ubiquitous glycosami
noglycan of the extracellular matrix, accumulates in the cortical and external medullary interstitium along with an increased expression of its main receptor, CD44, on inflammatory and tubular cells. Since the HA-CD44 pair may be involved in persistent post-ischemic inflammation, our research project aimed to determine the role of HA in the pathophysiology of renal IRI.
In a first attempt, we hypothesized that early accumulation of HA in experimental IRI may exert a deleterious effect, particularly through attracti
on of inflammatory cells. To verify this hypothesis, we used-methylumbelliferone (4-MU), a molecule that depletes the activated uridine diphosphate (UDP)-glucuronic acid precursor pool, to prevent HA accumulation in the post-ischemic kidney. To do so, C57BL/6 mice received a diet containing 4-MU during 14 weeks. At the end of the treatment, unilateral renal IR was performed and mice were euthanized 48h or 30 days post-IR.This study has revealed that inhibition of HA synthesis can prevent the development of severe renal lesions in both acute and chronic evolution of the post-ischemic kidney. In order to further determine the role of HA in the pathophysiological processes involved in renal IRI, we focused the second part of our study on the morpho-functional characterization of the post-
ischemic kidney of Hyal1-/- and Hyal2-/- mice. Indeed, HYAL1 and HYAL2 are the major hyaluronidases acting synergistically to degrade HA. Therefore, we
hypothesized that deficiency in either HYAL1 or HYAL2 could enhance accumulation of HA in the post-ischemic kidney of these knockout (KO) mice,
thereby, leading to an exacerbated inflammatory response and more severe renal damages compared to their wild type (WT) mice littermates. Before testi
ng this hypothesis, we first analyzed consequences of a lack of either HYAL1 or HYAL2 on renal function and renal HA accumulation in physiological
conditions. In this regard, the results revealed that kidney function was not impaired in both KO mice, even if they both displayed higher HA concentration
s in the plasma and in the kidney. Indeed, Hyal1-/- mice presented an accumulation of HA inside the proximal tubular cells whereas Hyal2-/- mice exhibited HA accumulation in the interstitial space of all kidney zones. Therefore, this part of our research project demonstrated that HYAL1 is necessary for the breakdown of intracellular HA in the cortex whereas
HYAL2 is essential for the degradation of extracellular HA throughout renal tissue. Thereafter, we performed unilateral renal IR on male Hyal1-/- and Hyal2-/- mice and euthanasia was performed 2, 7 or 30 days later. This study revealed that deficiency in either HYAL1 or HYAL2 leads to enhanced HA
accumulation in the post-ischemic kidney and consequently worsened inflammatory response, increased tubular damage, and fibrosis. According to the results obtained with size-exclusion chromatography, this might be related to the molecular weight of HA since we have demonstrated that both
Hyal1-/- and Hyal2 -/- mice exhibit a higher proportion of low molecular w
eight HA in the post-ischemic kidney in comparison to their respective WT mice littermates. In conclusion, our results demonstrate for the first time that HA plays a significant role in the pathogenesis of IRI, perhaps in part with its interaction with CD44. Indeed, HA-CD44 interaction leads to inflammatory processes, sustained macrophage recruitment, and progression to fibrosis. Moreover, we have also demonstrated that HYAL1 and HYAL2 display separate roles in clearing HA from the kidney, and can be described as "protective" against IRI deleterious consequences. Finally, we have confirmed that interfering with the HA cascade can be considered as a promising approach for the prevention of post-ischemic renal lesions and the progression to chronic kidney disease.

Date of Award	8 Mar 2016
Original language	English
Awarding Institution	University of Namur
Supervisor	Nathalie Caron (Supervisor)