Single photon emission computed tomography (SPECT) for functional investigation of the proximal tubule in conscious mice

Non-invasive analysis of renal function in conscious mice is necessary to optimize the use of mouse models. In this study, we evaluated whether single photon emission computed tomography (SPECT) using specific radionuclear tracers can be used to analyze changes in renal proximal tubule functions. The tracers included dimercaptosuccinic acid ((99m)Tc-DMSA), which is used for cortex imaging; 99mTc-mercaptoacetyltriglycine ((99m)Tc-MAG3), used for dynamic renography; and (123)I-beta2-microglobulin, which monitors receptor mediated endocytosis. (99m)Tc-DMSA SPECT imaging was shown to delineate the functional renal cortex with a ~1 mm spatial resolution and accumulated in the cortex reaching a plateau 5h after injection. The cortical uptake of (99m)Tc-DMSA was abolished in Clcn5 knock-out mice, a model of proximal tubule dysfunction. Dynamic renography with (99m)Tc-MAG3 in conscious mice demonstrated rapid extraction from blood, renal accumulation and subsequent tubular secretion. Anesthesia induced a significant delay in the (99m)Tc-MAG3 clearance. The tubular reabsorption of (123)I-beta2-microglobulin was strongly impaired in the Clcn5 knock-out mice, with defective tubular processing and loss of the native tracer in urine, reflecting proximal tubule dysfunction. Longitudinal studies in a model of cisplatin-induced acute tubular injury revealed a correlation between tubular recovery and (123)I-beta2-microglobulin uptake. These data show that SPECT imaging with well-validated radiotracers allows in vivo investigations of specific proximal tubule functions in conscious mice. Key words: Receptor-mediated endocytosis, Tubular secretion, ClC-5, Radionuclear tracers.