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Premature termination codon readthrough upregulates progranulin expression and improves lysosomal function in preclinical models of GRN deficiency.

ABSTRACT: BACKGROUND:Frontotemporal lobar degeneration (FTLD) is a devastating and progressive disorder, and a common cause of early onset dementia. Progranulin (PGRN) haploinsufficiency due to autosomal dominant mutations in the progranulin gene (GRN) is an important cause of FTLD (FTLD-GRN), and nearly a quarter of these genetic cases are due to a nonsense mutation. Premature termination codons (PTC) can be therapeutically targeted by compounds allowing readthrough, and aminoglycoside antibiotics are known to be potent PTC readthrough drugs. Restoring endogenous PGRN through PTC readthrough has not previously been explored as a therapeutic intervention in FTLD. METHODS:We studied whether the aminoglycoside G418 could increase PGRN expression in HEK293 and human induced pluripotent stem cell (hiPSC)-derived neurons bearing the heterozygous S116X, R418X, and R493X pathogenic GRN nonsense mutations. We further tested a novel substituted phthalimide PTC readthrough enhancer in combination with G418 in our cellular models. We next generated a homozygous R493X knock-in hiPSC isogenic line (R493X-/- KI), assessing whether combination treatment in hiPSC-derived neurons and astrocytes could increase PGRN and ameliorate lysosomal dysfunction relevant to FTLD-GRN. To provide in vivo proof-of-concept of our approach, we measured brain PGRN after intracerebroventricular administration of G418 in mice expressing the V5-tagged GRN nonsense mutation R493X. RESULTS:The R418X and R493X mutant GRN cell lines responded to PTC readthrough with G418, and treatments increased PGRN levels in R493X-/- KI hiPSC-derived neurons and astrocytes. Combining G418 with a PTC readthrough enhancer increased PGRN levels over G418 treatment alone in vitro. PGRN deficiency has been shown to impair lysosomal function, and the mature form of the lysosomal protease cathepsin D is overexpressed in R493X-/- KI neurons. Increasing PGRN through G418-mediated PTC readthrough normalized this abnormal lysosomal phenotype in R493X-/- KI neuronal cultures. A single intracerebroventricular injection of G418 induced GRN PTC readthrough in 6-week-old AAV-GRN-R493X-V5 mice. CONCLUSIONS:Taken together, our findings suggest that PTC readthrough may be a potential therapeutic strategy for FTLD caused by GRN nonsense mutations.

SUBMITTER: Frew J

PROVIDER: S-EPMC7075020 | biostudies-literature | 2020 Mar

REPOSITORIES: biostudies-literature

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Premature termination codon readthrough upregulates progranulin expression and improves lysosomal function in preclinical models of GRN deficiency.

Frew Jonathan J Baradaran-Heravi Alireza A Balgi Aruna D AD Wu Xiujuan X Yan Tyler D TD Arns Steve S Shidmoossavee Fahimeh S FS Tan Jason J Jaquith James B JB Jansen-West Karen R KR Lynn Francis C FC Gao Fen-Biao FB Petrucelli Leonard L Feldman Howard H HH Mackenzie Ian R IR Roberge Michel M Nygaard Haakon B HB

Molecular neurodegeneration 20200316 1

<h4>Background</h4>Frontotemporal lobar degeneration (FTLD) is a devastating and progressive disorder, and a common cause of early onset dementia. Progranulin (PGRN) haploinsufficiency due to autosomal dominant mutations in the progranulin gene (GRN) is an important cause of FTLD (FTLD-GRN), and nearly a quarter of these genetic cases are due to a nonsense mutation. Premature termination codons (PTC) can be therapeutically targeted by compounds allowing readthrough, and aminoglycoside antibiotic ...[more]

PMID: 32178712

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Project description:Premature termination codons (PTC) cause over 10% of genetic disease cases. Some aminoglycosides that bind to the ribosome decoding center can induce PTC readthrough and restore low levels of full-length functional proteins. However, concomitant inhibition of protein synthesis limits the extent of PTC readthrough that can be achieved by aminoglycosides like G418. Using a cell-based screen, we identified a small molecule, the phenylpyrazoleanilide Y-320, that potently enhances TP53, DMD, and COL17A1 PTC readthrough by G418. Unexpectedly, Y-320 increased cellular protein levels and protein synthesis, measured by SYPRO Ruby protein staining and puromycin labeling, as well as ribosome biogenesis measured using antibodies to rRNA and ribosomal protein S6. Y-320 did not increase the rate of translation elongation and it exerted its effects independently of mTOR signaling. At the single cell level, exposure to Y-320 and G418 increased ribosome content and protein synthesis which correlated strongly with PTC readthrough. As a single agent, Y-320 did not affect translation fidelity measured using a luciferase reporter gene but it enhanced misincorporation by G418. RNA-seq data showed that Y-320 up-regulated the expression of CXC chemokines CXCL10, CXCL8, CXCL2, CXCL11, CXCL3, CXCL1, and CXCL16. Several of these chemokines exert their cellular effects through the receptor CXCR2 and the CXCR2 antagonist SB225002 reduced cellular protein levels and PTC readthrough in cells exposed to Y-320 and G418. These data show that the self-limiting nature of PTC readthrough by G418 can be compensated by Y-320, a potent enhancer of PTC readthrough that increases ribosome biogenesis and protein synthesis. They also support a model whereby increased PTC readthrough is enabled by increased protein synthesis mediated by an autocrine chemokine signaling pathway. The findings also raise the possibility that inflammatory processes affect cellular propensity to readthrough agents and that immunomodulatory drugs like Y-320 might find application in PTC readthrough therapy.

Project description:BACKGROUND:Leukocyte adhesion deficiency 1 (LAD1) is an inherited disorder of neutrophil function. Nonsense mutations in the affected CD18 (ITB2) gene have rarely been described. In other genes containing such mutations, treatments with aminoglycoside types of antibiotics (e.g., gentamicin) were reported to partially correct the premature protein termination, by induction of readthrough mechanism. METHODOLOGY/PRINCIPAL FINDINGS:Genetic analysis was performed on 2 LAD1 patients. Expression, functional and immunofluorescence assays of CD18 in the patients were used to determine the in-vivo and in-vitro effects of gentamicin-induced readthrough. A theoretical modeling of the corrected CD18 protein was developed to predict the protein function. RESULTS:We found a novel premature termination codon, C562T (R188X), in exon 6 of the CD18 gene that caused a severe LAD1 phenotype in two unrelated Palestinian children. In-vivo studies on these patients' cells after gentamicin treatment showed abnormal adhesion and chemotactic functions, while in-vitro studies showed mislocalization of the corrected protein to the cytoplasm and not to the cell surface. A theoretical modeling of the corrected CD18 protein suggested that the replacement of the wild type arginine by gentamicin induced tryptophan at the position of the nonsense mutation, although enabled the expression of the entire CD18 protein, this was not sufficient to stabilize the CD18/11 heterodimer at the cell surface. CONCLUSION:A novel nonsense mutation in the CD18 gene causing a complete absence of CD18 protein and severe LAD1 clinical phenotype is reported. Both in vivo and in vitro treatments with gentamicin resulted in the expression of a corrected full-length dysfunctional or mislocalized CD18 protein. However, while the use of gentamicin increased the expression of CD18, it did not improve leukocyte adhesion and chemotaxis. Moreover, the integrity of the CD18/CD11 complex at the cell surface was impaired, due to abnormal CD18 protein and possibly lack of CD11a expression.

Dataset Information

Premature termination codon readthrough upregulates progranulin expression and improves lysosomal function in preclinical models of GRN deficiency.

Publications

Premature termination codon readthrough upregulates progranulin expression and improves lysosomal function in preclinical models of GRN deficiency.

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