Lowe syndrome patient cells display mTOR- and RhoGTPase-dependent phenotypes alleviated by rapamycin and statins

Abstract

Lowe syndrome (LS) is an X-linked developmental disease characterized by cognitive deficiencies, bilateral congenital cataracts and renal dysfunction. Unfortunately, this disease leads to the early death of affected children often due to kidney failure. Although this condition was first described in the early 1950s and the affected gene (OCRL1) was identified in the early 1990s, its pathophysiological mechanism is not fully understood and there is no LS-specific cure available to patients. Here we report two important signaling pathways affected in LS patient cells. While RhoGTPase signaling abnormalities led to adhesion and spreading defects as compared to normal controls, PI3K/mTOR hyperactivation interfered with primary cilia assembly (scenario also observed in other ciliopathies with compromised kidney function). Importantly, we identified two FDA-approved drugs able to ameliorate these phenotypes. Specifically, statins mitigated adhesion and spreading abnormalities while rapamycin facilitated ciliogenesis in LS patient cells. However, no single drug was able to alleviate both phenotypes. Based on these and other observations, we speculate that Ocrl1 has dual, independent functions supporting proper RhoGTPase and PI3K/mTOR signaling. Therefore, this study suggest that Ocrl1-deficiency leads to signaling defects likely to require combinatorial drug treatment to suppress patient phenotypes and symptoms.

Genotype & Phenotype in Lowe Syndrome: SpecificOCRL1patient mutations differentially impact cellular phenotypes

“…On the one hand, data presented in this study supports the hypothesis that some Ocrl1's functional roles are segregated within the protein primary structure (12,15,42). Specifically, that integrity of the N-terminus being mostly required for membrane remodeling functions (e.g., cell spreading (12)), while Ocrl1's C-terminal region is relevant for ciliogenesis (15).…”

“…Complementing the pioneering works by different authors (12)(13)(14)(15)(16)(36)(37)(38)(39)(40)(41)(42)(43)(44)(45) this study contributes to better understand Lowe syndrome as a complex disease. Here we highlight the heterogenous nature of this condition by focusing on the impact of different OCRL1 mutations on typical LS cellular phenotypes while reporting new abnormalities triggered by specific patient variants.…”

Participation of OCRL1, and APPL1, in the expression, proteolysis, phosphorylation and endosomal trafficking of megalin: Implications for Lowe Syndrome

“…Moreover, the reduction in insulin signaling evidenced in our experiments at the cellular level, specifically in conditions of reduction of OCRL1 function, not only would reduce megalin recycling but also would potentially decrease megalin endocytosis as pAKT is required for the efficient megalin-mediated endocytosis of albumin, a physiologically relevant ligand of the receptor present in the proximal tubule ( Silva-Aguiar et al, 2022 ). Regarding AKT activity, it has been recently found that the mTORC1 complex is inactivated in OCRL1 deficient cells ( Madhivanan et al, 2020 ), a defect that triggers a lack of nutrient-sensing ( Wang et al, 2021 ) due to mTORC1 is required for proper insulin signaling ( Saltiel and Kahn, 2001 ). Insulin signaling is also highly dependent on the cell type, something we observed in our experiments, and is associated with insulin receptor trafficking ( Iraburu et al, 2021 ).…”

The Future of Genetic Disease Studies: Assembling an Updated Multidisciplinary Toolbox

“…These studies were complemented by biochemical and cell biological assays to assess the mutational impact on protein function and availability ( De Leo et al, 2016 ; Ramadesikan et al, 2021 ). Furthermore, models were prepared by various methods to gain mechanistic insight into LS such as KO/morpholino zebrafish lines ( Coon et al, 2012 ; Ramirez et al, 2012 ; Gliozzi et al, 2020 ), humanized mouse models ( Bothwell et al, 2011 ), Ocrl1-deficient cells by CRISPR ( Madhivanan et al, 2020 ) along with stable lines expressing specific variants ( Ramadesikan et al, 2021 ), and patient-derived iPSCs ( Barnes et al, 2018 ; Hsieh et al, 2018 ; Liu et al, 2020 ; Akhtar et al, 2022 ). Taken together, LS research has greatly benefitted from the assimilation of a variety of techniques and is rapidly moving towards understanding LS in a patient mutation-specific manner to better guide the design novel therapeutic approaches.…”