*Purpose: Ischemia-reperfusion injury (IRI) is a major survival hurdle with kidney transplantation (KTX). Currently, no effective strategies for the prevention and treatment of IRI during KTX exist. Neuronal NO synthase beta (NOS1β) is the primary splice variant of NOS1 in the macula densa (MD) and contributes to most of the MD-NO generation, which blunts tubuloglomerular feedback (TGF) response and increases GFR. The role of MD- NOS1β modulated TGF response in the prevention of IRI and protection of transplanted graft function remains unknown.

*Methods: To test the response of NOS1 to tubular pH, bicarbonate or NH₄Cl were given for two weeks to C57BL/6 mice; then, KTXs were performed. Blood/urine pH, expression of NOS1, graft injury, and function were measured. We repeated the experiments in kidney-specific NOS1 knockout (KO) mice and compared the results with C57BL/6 mice.

*Results: The control showed moderate graft injury with plasma creatinine (Pcr) of 0.68 ± 0.13 mg/dl and reduced graft function (23% decrease in GFR) at 5 days post KTX. NOS1β expression decreased by 60%. TGF response measured by micropuncture was 4.1 ± 0.3 mmHg for sham-operated mice and 7.2 ± 0.9 mmHg for KTX mice, p<0.01. KO recipients showed more severe graft injury with Pcr of 1.07±0.14mg/dl (p<0.01), which demonstrated that deletion of NOS1 from macula densa significantly aggravated renal graft injury. The pH-NOS activity response curve showed that NOS1 was sensitive to tubular pH with an optimal pH of 8.0. Bicarbonate treatment increased NOS1 expression in the macula densa by 65%, while NH4Cl intake decreased the NOS1 expression by 40%. KTXs were performed in C57BL/6 and KO mice after two weeks of bicarbonate or NH₄Cl treatment. Pcr levels were about 30% and 100% lower in the bicarbonate-treated group than the vehicle and NH4Cl groups, respectively, indicating that bicarbonate treatment significantly alleviated graft injury. However, there were no significant differences in the graft injury for the KO mice among different groups.

*Conclusions: NOS1β expression in the macula densa decreases after KTX, which enhances TGF responsiveness and contributes to the decrease in GFR and decline of graft function. Rescue of NOS1β in the macula densa by renal alkalization decreases kidney injury and improves transplanted graft function.

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