In Vivo siRNA Delivery and Rebound of Renal LRP2 in Mice

siRNA stabilized for in vivo applications is filtered and reabsorbed in the renal proximal tubule (PT), reducing mRNA expression transiently. Prior siRNA efforts have successfully prevented upregulation of mRNA in response to injury. We proposed reducing constitutive gene and protein expression of LRP2 (megalin) in order to understand its molecular regulation in mice. Using siRNA targeting mouse LRP2 (siLRP2), reduction of LRP2 mRNA expression was compared to scrambled siRNA (siSCR) in mouse PT cells. Mice received siLRP2 administration optimized for dose, administration site, carrier solution, administration frequency, and administration duration. Kidney cortex was collected upon sacrifice. Renal gene and protein expression were compared by qRT-PCR, immunoblot, and immunohistochemistry (IHC). Compared to siSCR, siLRP2 reduced mRNA expression in PT cells to 16.6% ± 0.6%. In mouse kidney cortex, siLRP2 reduced mRNA expression to 74.8 ± 6.3% 3 h and 70.1 ± 6.3% 6 h after administration. mRNA expression rebounded at 12 h (160.6 ± 11.2%). No megalin renal protein expression reduction was observed by immunoblot or IHC, even after serial twice daily dosing for 3.5 days. Megalin is a constitutively expressed protein. Although LRP2 renal mRNA expression reduction was achieved, siRNA remains a costly and inefficient intervention to reduce in vivo megalin protein expression.