Lowe syndrome is a rare X-linked disorder characterized by bilateral congenital cataracts and glaucoma, mental retardation, and proximal renal tubular dysfunction. Mutations in OCRL, an inositol polyphosphate 5-phosphatase that dephosphorylates PI(4,5)P, cause Lowe syndrome. Previously we showed that OCRL localizes to the primary cilium, which has a distinct membrane phospholipid composition, but disruption of phosphoinositides in the ciliary membrane is poorly understood. Here, we demonstrate that cilia from Lowe syndrome patient fibroblasts exhibit increased levels of PI(4,5)P and decreased levels of PI4P. In particular, subcellular distribution of PI(4,5)P build-up was observed at the transition zone. Accumulation of ciliary PI(4,5)P was pronounced in mouse embryonic fibroblasts (MEFs) derived from Lowe syndrome mouse model as well as in -null MEFs, which was reversed by reintroduction of OCRL. Similarly, expression of wild-type OCRL reversed the elevated PI(4,5)P in Lowe patient cells. Accumulation of sonic hedgehog protein in response to hedgehog agonist was decreased in MEFs derived from a Lowe syndrome mouse model. Together, our findings show for the first time an abnormality in ciliary phosphoinositides of both human and mouse cell models of Lowe syndrome.
Glaucoma is a group of progressive optic neuropathies that cause irreversible vision loss. Although elevated intraocular pressure (IOP) is associated with the development and progression of glaucoma, the mechanisms for its regulation are not well understood. Here, we have designed CIBN/CRY2-based optogenetic constructs to study phosphoinositide regulation within distinct subcellular compartments. We show that stimulation of CRY2-OCRL, an inositol 5-phosphatase, increases aqueous humor outflow and lowers IOP in vivo, which is caused by a calcium-dependent actin rearrangement of the trabecular meshwork cells. Phosphoinositide stimulation also rescues defective aqueous outflow and IOP in a Lowe syndrome mouse model but not in IFT88fl/fl mice that lack functional cilia. Thus, our study is the first to use optogenetics to regulate eye pressure and demonstrate that tight regulation of phosphoinositides is critical for aqueous humor homeostasis in both normal and diseased eyes.
Mutations in PKD1 (encoding for polycystin-1 [PC1]) are found in 80%–85% of patients with autosomal dominant polycystic kidney disease (ADPKD). We tested the hypothesis that changes in actin dynamics result from PKD1 mutations through dysregulation of compartmentalized centrosomal RhoA signaling mediated by specific RhoGAP (ARHGAP) proteins resulting in the complex cellular cystic phenotype. Initial studies revealed that the actin cytoskeleton was highly disorganized in cystic cells derived from patients with PKD1 and was associated with an increase in total and centrosomal active RhoA and ROCK signaling. Using cilia length as a phenotypic readout for centrosomal RhoA activity, we identified ARHGAP5, -29, and -35 as essential regulators of ciliation in normal human renal tubular cells. Importantly, a specific decrease in centrosomal ARHGAP35 was observed in PKD1 -null cells using a centrosome-targeted proximity ligation assay and by dual immunofluorescence labeling. Finally, the ROCK inhibitor hydroxyfasudil reduced cyst expansion in both human PKD1 3D cyst assays and an inducible Pkd1 mouse model. In summary, we report a potentially novel interaction between PC1 and ARHGAP35 in the regulation of centrosomal RhoA activation and ROCK signaling. Targeting the RhoA/ROCK pathway inhibited cyst formation in vitro and in vivo, indicating its relevance to ADPKD pathogenesis and for developing new therapies to inhibit cyst initiation.
Background Lowe syndrome is a rare X-linked disease that is characterized by renal dysfunction, developmental delays, congenital cataracts and glaucoma. Mutations in the oculocerebral renal syndrome of Lowe ( OCRL) gene are found in Lowe syndrome patients. Although loss of vision is a major concern for families and physicians who take care of Lowe syndrome children, definitive cause of visual loss is still unclear. Children usually present with bilateral dense cataracts at birth and glaucoma, which occurs in more than half of cases, either concurrently or following cataract surgery. Materials and methods A retrospective review was conducted on the prevalence and characteristics of ocular findings among families of patients with Lowe syndrome with 137 uniquely affected individuals. Results Of 137 patients, all had bilateral congenital cataracts. Nystagmus was reported in 69.3% of cases, glaucoma in 54.7%, strabismus in 35.0%, and corneal scar in 18.2% of patients. Glaucoma was reported as the most common cause of blindness (46%) followed by corneal scars (41%). Glaucoma occurred in 54.7% of patients and affected both eyes in the majority of cases. Of these patients, 55% underwent surgery for glaucoma, while the remaining patients used medications to control their eye pressure. Timolol and latanoprost were the most commonly used medications. Although trabeculectomy and goniotomy are commonly used for pressure management, aqueous tube shunts had the best outcomes. Conclusion Ocular manifestations in individuals with Lowe syndrome and carriers with OCRL mutation are reported which may help familiarize clinicians with the ocular manifestations and management of a rare and complex syndrome.
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