PIN1 and osteoporosis: Pin1 is expressed in numerous organs including the lung, liver, stomach, brain, heart, kidney, and spleen (Ryo et al., 2001) and may be a key factor associated with many metabolic pathways; Pin1 knockout (KO) mice are born and live to an old age (Fujimori et al., 1999) but develop weight loss, osteoporosis, skin atrophy, retinal degeneration, genital atrophy, and impaired motor coordination (Fujimori et al., 1999).