Pathogenic variants of sphingomyelin synthase SMS2 disrupt lipid landscapes in the secretory pathway
- Osnabrück University, Germany
- Danish Cancer Society, Denmark
- Université de Strasbourg, UMR 7021, CNRS, France
- University of Utah, United States
- Utrecht University, Netherlands
- University of Helsinki, Finland
- Yale University, United States
Abstract
Sphingomyelin is a dominant sphingolipid in mammalian cells. Its production in the trans-Golgi traps cholesterol synthesized in the ER to promote formation of a sphingomyelin/sterol gradient along the secretory pathway. This gradient marks a fundamental transition in physical membrane properties that help specify organelle identify and function. We previously identified mutations in sphingomyelin synthase SMS2 that cause osteoporosis and skeletal dysplasia. Here we show that SMS2 variants linked to the most severe bone phenotypes retain full enzymatic activity but fail to leave the ER owing to a defective autonomous ER export signal. Cells harboring pathogenic SMS2 variants accumulate sphingomyelin in the ER and display a disrupted transbilayer sphingomyelin asymmetry. These aberrant sphingomyelin distributions also occur in patient-derived fibroblasts and are accompanied by imbalances in cholesterol organization, glycerophospholipid profiles and lipid order in the secretory pathway. We postulate that pathogenic SMS2 variants undermine the capacity of osteogenic cells to uphold nonrandom lipid distributions that are critical for their bone forming activity.
Data availability
All data generated or analysed during this study are included in the manuscript and supporting file. Source Data files have been provided for Figures 2-4, 7-9 and Appendix 1 - figure 3.
Article and author information
Author details
Christopher G Burd
Funding
Deutsche Forschungsgemeinschaft (SFB944-P14)
- Joost CM Holthuis
Deutsche Forschungsgemeinschaft (HO3539/1-1)
- Joost CM Holthuis
Deutsche Forschungsgemeinschaft (SFB944-P8)
- Jacob Piehler
National Institutes of Health (R35 GM144096)
- Christopher G Burd
The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication.
Copyright
© 2022, Sokoya et al.
This article is distributed under the terms of the Creative Commons Attribution License permitting unrestricted use and redistribution provided that the original author and source are credited.
Metrics
-
- 2,671
- views
-
- 554
- downloads
-
- 22
- citations
Views, downloads and citations are aggregated across all versions of this paper published by eLife.
Download links
A two-part list of links to download the article, or parts of the article, in various formats.
Downloads (link to download the article as PDF)
Open citations (links to open the citations from this article in various online reference manager services)
Cite this article (links to download the citations from this article in formats compatible with various reference manager tools)
Pathogenic variants of sphingomyelin synthase SMS2 disrupt lipid landscapes in the secretory pathway
eLife 11:e79278.
https://doi.org/10.7554/eLife.79278
Further reading
-
- Biochemistry and Chemical Biology
N 6,2’-O-dimethyladenosine (m6Am) is a modified nucleotide located at the first transcribed position in mRNA and snRNA that is essential for diverse physiological processes. m6Am mapping methods assume each gene uses a single start nucleotide. However, gene transcription usually involves multiple start sites, generating numerous 5’ isoforms. Thus, gene-level annotations cannot capture the diversity of m6Am modification in the transcriptome. Here, we describe CROWN-seq, which simultaneously identifies transcription-start nucleotides and quantifies m6Am stoichiometry for each 5’ isoform that initiates with adenosine. Using CROWN-seq, we map the m6Am landscape in nine human cell lines. Our findings reveal that m6Am is nearly always a high stoichiometry modification, with only a small subset of cellular mRNAs showing lower m6Am stoichiometry. We find that m6Am is associated with increased transcript expression and provide evidence that m6Am may be linked to transcription initiation associated with specific promoter sequences and initiation mechanisms. These data suggest a potential new function for m6Am in influencing transcription.
-
- Biochemistry and Chemical Biology
- Structural Biology and Molecular Biophysics
African trypanosomes are the causative agents of neglected tropical diseases affecting both humans and livestock. Disease control is highly challenging due to an increasing number of drug treatment failures. African trypanosomes are extracellular, blood-borne parasites that mainly rely on glycolysis for their energy metabolism within the mammalian host. Trypanosomal glycolytic enzymes are therefore of interest for the development of trypanocidal drugs. Here, we report the serendipitous discovery of a camelid single-domain antibody (sdAb aka Nanobody) that selectively inhibits the enzymatic activity of trypanosomatid (but not host) pyruvate kinases through an allosteric mechanism. By combining enzyme kinetics, biophysics, structural biology, and transgenic parasite survival assays, we provide a proof-of-principle that the sdAb-mediated enzyme inhibition negatively impacts parasite fitness and growth.
