EXPERIMENTAL ISCHEMIA (2014)

Introduction and Aims: Renal ischemia-reperfusion injury (IRI) is a pathological process that may lead to acute renal failure and chronic dysfunction in renal allografts. Hyaluronan (HA) is a glycosaminoglycan present in the extracellular matrix involved in many biological processes such as wound healing and inflammation. During IRI, HA accumulation and expression of its principal receptor CD44 increased dramatically and concomitantly throughout the kidney. These observations may be related to specific modulation of HA synthases activity and/or to reduced HA degradation that is mainly achieved in the kidney by two hyaluronidases, HYAL1 and HYAL2. Interestingly, we previously demonstrated that suppression of HA accumulation during IRI, using 4-MU as an inhibitor of HA synthesis, protected the kidney from ischemic insults. Therefore, in the present study, we hypothesized that Hyal1-/-and Hyal2-/-mice, should display an exacerbated inflammatory response leading to more severe renal damages due to a higher HA accumulation in the post-ischemic kidney compared to the wild type littermates. Methods: Male Hyal1-/-and Hyal2-/-mice, as well as wild type (WT) littermates were subjected to 28 min of left kidney ischemia followed by a contralateral nephrectomy. Mice were euthanized either 48h or 7 days post-IRI, blood sample was collected and the kidney was harvested for analytical purposes. Creatininemia was measured as an indicator of renal function and HA expression was evaluated either by histochemistry and ELISA. Renal inflammatory response and CD44 expression were also assessed in the post-ischemic kidney using different analytical tools. Results: In both Hyal1-/-and Hyal2-/-mice, HA content in the control or in the post-ischemic kidney was nearly 45% higher compared to those measured in WT mice. Creatininemia was increased in both KO mice compared to the WT 48h post-IRI (Hyal1: 674 vs 585 M, P<0.05; Hyal2: 688 vs 507 M, P<0.05). Histopathological damages, characterized by necrotic and cystic tubules, were similar 48h after IRI in both KO and WT mice. Regarding inflammation, Hyal1-/-and Hyal2-/-mice presented a higher concentration of MIP-2 in the post-ischemic kidney in comparison to the WT (Hyal1: 2363192 vs 1076239 pg/g of proteins, P<0.05; Hyal2: 1431227 vs 793116 pg/g of proteins, P<0.05). Infiltration of macrophages into the kidney was similar in both groups. Seven days after IRI, histopathological lesions were more severe in KO mice than in WT mice and macrophages infiltration was also significantly higher (Hyal1: 20112 vs 12617 cells/mm2, P<0.05; Hyal2: 17510 vs 13024 cells/mm2, P<0.05). Proliferation, attested by PCNA immunostaining (% of PCNA-positive cells), was also significantly increased in both KO mice (Hyal1: 306 vs 145 %, P<0.05; Hyal2: 374 vs 184%, P<0.05). CD44 receptor was also up-regulated in both KO mice. Fibrotic markers, such as -SMA and collagen types I and III, were also increased 7 days after IRI in both KO mice. Conclusions: Our results demonstrate a protective role of HYAL1 and HYAL2 against IRI most likely by reducing HA accumulation in the post-ischemic kidney, thereby decreasing the inflammatory processes leading to acute kidney injury. Suppression of HA accumulation during IR injury may protect renal function against ischemic insults.