Antibody-mediated rejection (ABMR) is a leading cause for renal transplant loss. Fischer-344 (F344) to Lewis rat model of kidney transplantation without immunosuppression closely reflects the glomerular changes of active ABMR in humans at 6 weeks, culminating in transplant glomerulopathy with secondary glomerulosclerosis at 23 weeks after transplantation. miRNAs regulate entire pathways by suppressing target gene expression, yet their involvement in ABMR is incompletely understood. We investigated glomerular miRNA expression changes associated with ABMR activity with the goal of informing an antagomir-based therapy for secondary prevention of glomerular scarring in animals with full-blown ABMR.
We searched for differential glomerulocapillary miRNA expression in F344 to Lewis rat model without immunosuppression with low-density qRT-PCR arrays on microdissected paraffin tissue. miRNAs differentially expressed between cohorts and correlating with histopathological ABMR activity were confirmed in single qRT-PCR runs. Promising therapeutic targets of confirmed miRNAs were investigated in silico. To validate our results and investigate the therapeutic potential of our findings, we injected antagomir against rno-miR-199a-3p or scrambled controls intravenously at 8 weeks after transplantation. Serum creatinine values were compared and animals were sacrificed 23 weeks after transplantation and assessed for glomerulosclerosis.
11 glomerulocapillary miRNAs were differentially expressed between cohorts and six candidate miRNAs correlating with ABMR activity were retained for confirmation. Glomerular rno-miR-125b-2-3p was confirmed as upregulated in early 9 day allografts. rno-miR-199a-3p was significantly higher in 26 week allografts than in native controls. In contrast, rno-miR-451a was confirmed as upregulated in 9 day and 6 week isografts. Experimentally validated and predicted gene targets of these 3 miRNAs indicated detrimental effects of the first two and protective effects of the latter miRNA. The anti-rno-miR-199a-3p antagomir group had significantly lower serum creatinine at 8 weeks after injection than scrambled controls and, in the animals sacrificed so far, a lower glomerulosclerosis index.
F344 to Lewis rat model is characterized by a distinct glomerulocapillary miRNA signature of ABMR activity. This miRNA signature with two miRNAs upregulated in allografts (rno-miR-125b-2-3p, rno-miR-199a-3p) and one miRNA upregulated in isografts (rno-miR-451-5p) and their target pathways shed new light on the pathogenesis of ABMR. Our preliminary data about secondary prevention of glomerulosclerosis associated with ABMR after development of full-blown active ABMR with an antagomir against rno-miR-199a-3p seems to validate our results and is encouraging but needs confirmation with histopathological examination of the full cohort.