The Rho-kinases, Rock1 and Rock2, regulate cell shape/cytoskeletal rearrangement downstream of the RhoA small GTPase. These processes are critical to many cellular functions including contraction, proliferation, motility, and viability. As aberrant kinase activity is seen in cardiovascular and autoimmune diseases and cancers, the development of selective inhibitors is an active area of pharmaceutical research. While acute perturbation of this pathway is tolerated, it is unclear whether Rho-kinases have homeostatic functions, precluding blockade for chronic conditions. Here, we used inducible gene targeting to ablate Rock1 and Rock2 individually or together in adult mice, and found an obligate requirement for these enzymes in maintaining stem cell viability and proliferative capacity. Rock1flox/flox, Rock2 flox/flox, or Rock1 flox/flox: Rock2 flox/flox mice were crossed to the Rosa26-Cre ERT2 line to delete the floxed alleles with tamoxifen. Loss of either allele did not impact survival, indicating functional redundancy between the kinases, however combined deletion caused rapid mortality. Histological evaluation revealed tissue homeostasis was disturbed in organs with rapid cell turnover and renewal, such as the alimentary tract and lymphoid tissues. Particularly, crypt regeneration within the small intestine was severely compromised, impeding nutrient absorption, promoting systemic inflammation and subsequent lethality. Mutant intestinal stem cells displayed mitotic arrest due to defective cytokinesis, signaling cell death. Similarly, cycling of hematopoietic stem cells was blocked, causing severe cytopenia. Thus, given this fundamental role in stem cell renewal and tissue homeostasis, Rho-kinase inhibition is not a viable therapy for chronic diseases.
Rajita Pappu– Senior Scientist, GENENTECH