Kidney targeted radiotherapy attenuates the renal ischemia-reperfusion injury in mice

BACKGROUND
Whole-body irradiation has been associated with renal ischemic preconditioning in mice. Here, we investigate the functional and fundamental impact of radiotherapy centered on the kidneys before renal ischemia/reperfusion (I/R) in mice.

METHODS
Experience1: Animals (n=6) were anesthetized and placed in the irradiator. Two beams of X-rays (225Kv, 13 mA) specifically targeted both kidneys to deliver a dose a 8,56Gy. One month later, a right nephrectomy was performed, and a left renal ischemia was induced for 30min. After 48 hours of reperfusion, the left kidney was collected, as well as blood. Control group (n=6) underwent a similar renal I/R procedure, with no prior irradiation. Experience 2: Unilateral irradiation of the left kidney (8.56 Gy) was performed in mice (n=10). One month later, the left (irradiated) kidney was collected. Additionally, the left kidneys were collected from non-irradiated mice (n=5). Total RNAs were extracted from irradiated and control kidneys to perform comparative high-throughput RNA-Seq. BaseSpace Sequence Hub Illumina was used. Functional enrichment analysis was performed using DAVID program. Both experimental protocols have been approved by the IACUC of ULiège, Liège, Belgium.

RESULTS
Following kidney I/R, blood urea nitrogen (BUN) levels were significantly lower in pre-irradiated mice (148.4±93.1) compared to controls (495.7±33.3, p<0.01). The number of PCNA-positive proliferating cells was significantly lower in pre-irradiated mice (130.8±52.7) compared to controls (545.4±257.3, p<0.001). The renal infiltration by inflammatory CD11b-positive cells (90.2±32.2 vs. 414.5±148.6) and F4-80-positive macrophages (80.6±22.9 vs. 178.5±68) was significantly reduced in pre-irradiated animals vs. controls. Comparative transcriptomics showed a significant up-regulation of various signaling pathways, including angiogenesis (HMOX1) and stress response (HSPA1A, HSPA1B), and a down-regulation of oxidoreduction (NOX4).

CONCLUSION
Kidney irradiation induces ischemic preconditioning in mice, with improved renal function and decreased inflammation following renal I/R. The aforementioned signaling pathways may play a role in irradiation-associated kidney resistance to I/R.