Date Published: February 14, 2018
Publisher: Public Library of Science
Author(s): Wen-Chieh Hsieh, Swetha Ramadesikan, Donna Fekete, Ruben Claudio Aguilar, Austin John Cooney.
Lowe syndrome is an X-linked condition characterized by congenital cataracts, neurological abnormalities and kidney malfunction. This lethal disease is caused by mutations in the OCRL1 gene, which encodes for the phosphatidylinositol 5-phosphatase Ocrl1. While in the past decade we witnessed substantial progress in the identification and characterization of LS patient cellular phenotypes, many of these studies have been performed in knocked-down cell lines or patient’s cells from accessible cell types such as skin fibroblasts, and not from the organs affected. This is partially due to the limited accessibility of patient cells from eyes, brain and kidneys. Here we report the preparation of induced pluripotent stem cells (iPSCs) from patient skin fibroblasts and their reprogramming into kidney cells. These reprogrammed kidney cells displayed primary cilia assembly defects similar to those described previously in cell lines. Additionally, the transcription factor and cap mesenchyme marker Six2 was substantially retained in the Golgi complex and the functional nuclear-localized fraction was reduced. These results were confirmed using different batches of differentiated cells from different iPSC colonies and by the use of the human proximal tubule kidney cell line HK2. Indeed, OCRL1 KO led to both ciliogenesis defects and Six2 retention in the Golgi complex. In agreement with Six2’s role in the suppression of ductal kidney lineages, cells from this pedigree were over-represented among patient kidney-reprogrammed cells. We speculate that this diminished efficacy to produce cap mesenchyme cells would cause LS patients to have difficulties in replenishing senescent or damaged cells derived from this lineage, particularly proximal tubule cells, leading to pathological scenarios such as tubular atrophy.
The Oculo-Cerebro-Renal syndrome of Lowe (OCRL), also known as Lowe syndrome (LS) is a genetic disease caused by mutations in the OCRL1 gene which encodes for an inositol 5-phosphatase (EC 126.96.36.199) . This X-linked condition is characterized by bilateral cataracts at birth, mental retardation and kidney malfunction, with the latter being the most common cause of death of affected children [1,2]. Specifically, patients display tubulopathy and Fanconi-like syndrome that often evolves into kidney failure [1,3,4]. However, how these clinical manifestations develop is still poorly understood.
A variety of cellular phenotypes associated with Ocrl1-deficiency have been described, including phosphatidylinositol (4, 5) bisphosphate [PI(4, 5)P2] accumulation [17,18], actin and RhoGTPase regulation abnormalities [17,19–23], trafficking [17,24–27] and ciliogenesis abnormalities [5–8]. However, most of these phenotypes have been observed under Ocrl1 knock-down conditions and/or in LS patient skin fibroblasts.
LS is a devastating genetic disease that despite being described more than 60 years ago, still lacks a clear delineation of its pathomechanism and no specific cure is available. Among multiple factors contributing to such a scenario, lack of understanding of developmental abnormalities in place and uneven availability of patient cells from affected organs are likely some of them. Here we describe the derivation of iPSCs from LS patient skin fibroblasts and their reprogramming as kidney cells. These kidney-differentiated cells displayed a PC assembly defect, opening the possibility that this phenotype contributes to observed LS renal abnormalities. Interestingly, we also found that in LS cells the balance between ductal and cap mesenchyme kidney lineages is skewed toward the former. In addition, we observed a significant decrease in the fraction of LS cells displaying nuclear localization of the transcription factor Six2, a cap mesenchyme marker that acts as repressor of ductal lineage differentiation. In fact, LS cells displayed a significantly increased pool of Six2 localized at the Golgi complex as compared to normal cells.