Recovery of PEX1-Gly843Asp peroxisome dysfunction by small-molecule compounds Rui Zhanga, Li Chena, Sarn Jiralerspongb, Ann Snowdenc, Steven Steinbergc, and Nancy Bravermanb,1 aMcKusick-Nathans Institute of Genetic Medicine, The Johns Hopkins University, Baltimore, MD 21205; bMontreal Children’s Hospital Research Institute, McGill University, Montreal, QC H3Z 2Z3, Canada; and cDepartment of Neurogenetics, Kennedy Krieger Institute, Baltimore, MD 21205 Edited by William S. Sly, St. Louis University School of Medicine, St. Louis, MO, and approved February 11, 2010 (received for review January 8, 2010) Zellweger spectrum disorder (ZSD) is a heterogeneous group of transcript level in these patients is normal (10), it is likely that diseases with high morbidity and mortality caused by failure to the PEX1-p.G843D is misfolded and degraded. PEX1 is an AAA assemble normal peroxisomes. There is no therapy for ZSD, but (ATPase associated with diverse cellular activities) ATPase that management is supportive. Nevertheless, one-half of the patients oligomerizes with PEX6 AAA ATPase and when complexed to have a phenotype milder than classic Zellweger syndrome and PEX26, recycles PEX5 from the peroxisome membrane to the exhibit a progressive disease course. Thus, patients would benefit cytosol (11). The interaction between PEX1-p.G843D and PEX6 is if therapies became available and were instituted early. Recent reduced to less than 70% of wild type (12). Peroxisome functions reports indicate several interventions that result in partial perox- also recover when PEX6 is overexpressed in PEX1-p.G843D cells, isome recovery in ZSD fibroblasts. To identify drugs that recover consistent with conformational rescue by a binding partner (12). peroxisome functions, we expressed a GFP-peroxisome targeting Finally, when ZSD fibroblasts, including those containing PEX1-p. signal 1 reporter in fibroblasts containing the common disease G843D, are cultured in 4-phenylbutyrate, peroxisome numbers allele, PEX1-p.Gly843Asp. The GFP reporter remained cytosolic at increase 2- to 3-fold and functions improve (13). Overall, these baseline, and improvement in peroxisome functions was detected observations suggest that patient defects are amenable to inter- by the redistribution of the GFP reporter from the cytosol to the vention at the cellular level and implicate peroxin stabilization and peroxisome. We established a high-content screening assay based peroxisome proliferation as mechanisms that drugs could recapit- on this phenotype assay and evaluated 2,080 small molecules. The ulate. We sought to develop a high-throughput assay to screen cells were cultured in chemical for 2 days and then, were fixed and small-molecule libraries and identify drugs that may be further MEDICAL SCIENCES fl imaged by epi uorescent microscopy on a high-content imaging developed into clinical therapy. Identified compounds can serve as fi platform. We identi ed four compounds that partially recover starting points for the development of others with optimal fi matrix protein import, and we con rmed three using independent pharmacologic profiles. assays. Our results suggest that PEX1-p.G843D is a misfolded pro- tein amenable to chaperone therapy. Results Development of a High-Throughput Assay. We chose to test PEX1-p. Zellweger spectrum | AAA ATPase | misfolded protein | chemical G843D, a missense allele rescued by the mechanisms discussed screening | pharmacologic chaperone and accounting for one-third of all ZSD alleles. To monitor PEX1 function, a primary cell line, heterozygous for the common PEX1 he peroxisome biogenesis disorders, including Zellweger alleles p.G843D and I700fs, was transformed, immortalized, and Tspectrum disorder (ZSD) and Rhizomelic chondrodysplasia transfected with a GFP-peroxisome targeting signal 1 (PTS1) punctata (RCDP), are a heterogeneous group of autosomal re- reporter. A stable clone was selected; we refer to these cells as PEX1- cessive diseases caused by mutations in PEX genes. Among the G843D-PTS1, because the second allele is null (10). We verified that mutations identified in ZSD, the PEX1-p.Gly843Asp or G843D GFP-PTS1 remains predominantly cytosolic in these cells when (c.2528G > A) founder allele occurs in high frequency in patients cultured at 37 °C (Fig. 1, untreated). After 2 days at 30 °C, we of European origin (1). The presence of at least one PEX1-p. observed redistribution of GFP-PTS1 from the cytosol to punctate G843D allele predicts a phenotype milder than classic Zellweger structures, indicating recovery of PTS1 matrix-protein import syndrome (ZS) (2). Overall, the milder phenotypes, neonatal (Fig. 1, 30 °C). Because lower temperature recovers matrix-pro- adrenoleukodystrophy (NALD) and infantile Refsum disease tein import, we predicted that nonspecific chemical chaperones (IRD), are associated with missense alleles in PEX genes, less would also recover matrix-protein import. Chemical chaperones severe biochemical deficiencies, and more functional peroxi- are small-molecule osmolytes, such as glycerol, DMSO, amino somes, findings consistent with residual peroxin function. acids and trimethylamines, including trimethylamine N-oxide When fibroblasts from NALD-IRD patients are cultured at (TMAO), and betaine (trimethylglycine). The mechanism for 30 °C, peroxisome biogenesis improves. This was noted for cell their chaperone function is unknown, but might include con- lines with missense alleles in PEX1 (G843D) (3), PEX2 (E55K) formational correction and prevention of nonproductive protein (4), PEX6 (G572I, I845T, L57P) (5, 6), PEX26 (R98W, L45P) (7), interactions (14). To evaluate these chemicals, PEX1-G843D- and PEX13 (I326T) (8) and suggests reduced protein misfolding PTS1 cells were seeded in 96-well plates and cultured at 37 °C. at lower temperature (9). In contrast, ZS cell lines did not re- Chemical was added the next day, and after 2 days, we observed spond. These studies showed increased peroxisome number and robust recovery of punctate GFP-PTS1 in 3% DMSO, 200 mM improved import, matrix protein processing, very long chain fatty TMAO, 5% glycerol, 100 mM betaine, and 300 mM proline acid (VLCFA) oxidation, and plasmalogen biosynthesis. Over- expression of PEX missense alleles in CHO cells null for the corresponding peroxin conferred the temperature-sensitive phe- Author contributions: R.Z., S.S., and N.B. designed research; R.Z., L.C., S.J., A.S., S.S., and N.B. notype, directly implicating the expressed protein in causing this performed research; R.Z., S.S., and N.B. analyzed data; and N.B. wrote the paper. phenotype (7). The authors declare no conflict of interest. Several groups have studied PEX1-p.G843D. Walter et al. (3) This article is a PNAS Direct Submission. showed markedly reduced levels (5–15%) compared with wild- 1To whom correspondence should be addressed. E-mail: [email protected]. fi type PEX1 in broblast lysates from patients homozygous for This article contains supporting information online at www.pnas.org/cgi/content/full/ this mutation and a 2- to 3-fold increase at 30 °C. Because PEX1 0914960107/DCSupplemental. www.pnas.org/cgi/doi/10.1073/pnas.0914960107 PNAS Early Edition | 1of6 Downloaded by guest on September 27, 2021 Fig. 1. Response to nonspecific chemical chaperones in PEX1-G843D-PTS1 cells. Cells were cultured for 2 days at 30 °C or 37 °C with chemical and imaged live (30 °C; glycerol and DMSO) or after fixation (the remainder). Note the redistribution of GFP-PTS1 from the cytosol to the peroxisome in the treated groups; results were similar for 300 mM proline. In the lower right two images, cells cultured in TMAO were permeabilized and incubated with PEX14 antiserum and Texas Red conjugated secondary antibody. Colocalization of PEX14 and GFP is shown in the last image. (Fig. 1). To confirm that the punctate structures were perox- column). For each condition, plasmalogen biosynthesis improved isomes, we performed indirect immunofluorescence (IF) with significantly compared with the untreated results. antiserum to the membrane peroxin, PEX14, and all punctate Finally, we evaluated the recovery of PTS2 protein processing GFP structures colocalized with peroxisome membranes (Fig. 1 by immunoblotting (Fig. 2). Mammalian PTS2 proteins are thi- GFP-PTS1, PEX14). olase, phytanoyl-CoA hydroxylase (PhyH), and alkylglycerone To show that recovery of GFP-PTS1 targeting is a reliable phosphate synthase (AGPS). After import of these preproteins, a indicator of the recovery of functional peroxisomes, we evaluated PTS1 matrix protease removes the N-terminal PTS2 sequence, peroxisome functions by three independent assays. First, we generating a smaller, mature protein (15). The relative increase evaluated the recovery of endogenous matrix protein import by IF in this maturation step should reflect the recovery of both PTS1 using primary fibroblasts homozygous for PEX1-p.G843D. Cells and PTS2 import observed in the previous experiments. PEX1-p. were cultured at 37 °C in glycerol and TMAO or at 30 °C without G843D primary fibroblasts were incubated for 2 days with non- chemicals for 2 days. Then, they were fixed, permeabilized, and specific chaperones, and immunoblotting was performed on incubated with antiserum to the PTS2 matrix protein (thiolase) whole cell lysates. Results were interpreted by comparing the and catalase. Thiolase import enabled us to assess the competency amounts of unprocessed to mature protein in untreated and of the PTS2 import pathway. Although catalase uses the PTS1 treated samples. We observed a relative increase