Anti-LGR4 monoclonal antibody, clone 23I7

The development of the anterior segment of the mammalian eye is critical for normal ocular function, whereas abnormal development can cause glaucoma, a leading cause of blindness in the world. We report that orphan G protein-coupled receptor 48 (Gpr48/LGR4) plays an important role in the development of the anterior segment structure. Disruption of Gpr48 causes a wide spectrum of anterior segment clysgenesis (ASD), including microphthalmia, iris hypoplasia, ircliocorneal angle malformation, cornea clysgenesis, and cataract. Detailed analyses reveal that defective iris myogenesis and ocular extracellular matrix homeostasis are detected at early postnatal stages of eye development, whereas ganglion cell loss, inner nuclear layer thinness, and early onset of glaucoma were detected in 6-month-old Gpr48(-/-) mice. To determine the molecular mechanism of ASD caused by the deletion of Gpr48, we performed gene expression analyses and revealed dramatic down-regulation of PitK2 in homozygous knockout mice. In vitro studies with the constitutively active Gpr48 mutant receptor demonstrate that Pitx2 is a direct target of the Gpr48-mediated cAMP-CREB signaling pathway in regulating anterior segment development, suggesting a role of Gpr48 as a potential therapeutic target of ASD.

Cerebellar dysfunction causes ataxia characterized by loss of balance and coordination. Until now, the molecular and neuronal mechanisms of several types of inherited cerebellar ataxia have not been completely clarified. Here, we report that leucine-rich G protein-coupled receptor 4 (Lgr4/Gpr48) is highly expressed in Purkinje cells (PCs) in the cerebellum. Deficiency of Lgr4 leads to an ataxia-like phenotype in mice. Histologically, no obvious morphological changes were observed in the cerebellum of Lgr4 mutant mice. However, the number of PCs was slightly but significantly reduced in Lgr4(-/-) mice. In addition, in vitro electrophysiological analysis showed an impaired long term depression (LTD) at parallel fiber-PC (PF-PC) synapses in Lgr4(-/-) mice. Consistently, immunostaining experiments showed that the level of phosphorylated cAMP-responsive element-binding protein (Creb) was significantly decreased in Lgr4(-/-) PCs. Furthermore, treatment with forskolin, an adenylyl cyclase agonist, rescued phospho-Creb in PCs and reversed the impairment in PF-PC LTD in Lgr4(-/-) cerebellar slices, indicating that Lgr4 is an upstream regulator of Creb signaling, which is underlying PF-PC LTD. Together, our findings demonstrate for first time an important role for Lgr4 in motor coordination and cerebellar synaptic plasticity and provide a potential therapeutic target for certain types of inherited cerebellar ataxia.