Hypomorphic mutations of TRIP11 cause odontochondrodysplasia
Anika Wehrle, Tomasz M. Witkos, Sheila Unger, Judith Schneider, John A. Follit, Johannes Hermann, Tim Welting, Virginia Fano, Marja Hietala, Nithiwat Vatanavicharn, Katharina Schoner, Jürgen Spranger, Miriam Schmidts, Bernhard Zabel, Gregory J. Pazour, Agnes Bloch-Zupan, Gen Nishimura, Andrea Superti-Furga, Martin Lowe, Ekkehart Lausch
Anika Wehrle, Tomasz M. Witkos, Sheila Unger, Judith Schneider, John A. Follit, Johannes Hermann, Tim Welting, Virginia Fano, Marja Hietala, Nithiwat Vatanavicharn, Katharina Schoner, Jürgen Spranger, Miriam Schmidts, Bernhard Zabel, Gregory J. Pazour, Agnes Bloch-Zupan, Gen Nishimura, Andrea Superti-Furga, Martin Lowe, Ekkehart Lausch
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Research Article Bone biology Genetics

Hypomorphic mutations of TRIP11 cause odontochondrodysplasia

Abstract

Odontochondrodysplasia (ODCD) is an unresolved genetic disorder of skeletal and dental development. Here, we show that ODCD is caused by hypomorphic TRIP11 mutations, and we identify ODCD as the nonlethal counterpart to achondrogenesis 1A (ACG1A), the known null phenotype in humans. TRIP11 encodes Golgi-associated microtubule-binding protein 210 (GMAP-210), an essential tether protein of the Golgi apparatus that physically interacts with intraflagellar transport 20 (IFT20), a component of the ciliary intraflagellar transport complex B. This association and extraskeletal disease manifestations in ODCD point to a cilium-dependent pathogenesis. However, our functional studies in patient-derived primary cells clearly support a Golgi-based disease mechanism. In spite of reduced abundance, residual GMAP variants maintain partial Golgi integrity, normal global protein secretion, and subcellular distribution of IFT20 in ODCD. These functions are lost when GMAP-210 is completely abrogated in ACG1A. However, a similar defect in chondrocyte maturation is observed in both disorders, which produces a cellular achondrogenesis phenotype of different severity, ensuing from aberrant glycan processing and impaired extracellular matrix proteoglycan secretion by the Golgi apparatus.

Authors

Anika Wehrle, Tomasz M. Witkos, Sheila Unger, Judith Schneider, John A. Follit, Johannes Hermann, Tim Welting, Virginia Fano, Marja Hietala, Nithiwat Vatanavicharn, Katharina Schoner, Jürgen Spranger, Miriam Schmidts, Bernhard Zabel, Gregory J. Pazour, Agnes Bloch-Zupan, Gen Nishimura, Andrea Superti-Furga, Martin Lowe, Ekkehart Lausch

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Figure 8

Normal global secretory traffic but defective glycan processing by the Golgi apparatus in odontochondrodysplasia (ODCD).

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Normal global secretory traffic but defective glycan processing by the G...
(A) Pulse-chase analysis of protein secretion of control and patient fibroblasts. Cells were starved for 1 hour in methionine- and cysteine-free medium and pulsed for 20 minutes with fresh starvation medium containing 50 μCi/ml [35S]methionine and [35S]cysteine protein labeling mix. Cells were chased in medium containing unlabeled methionine and cysteine for 0, 30, or 60 minutes and lysed. Radiolabeled cellular (cells) and secreted (medium) proteins, which were precipitated by trichloroacetic acid, were subjected to sodium dodecyl sulfate polyacrylamide gel electrophoresis and visualized by phosphor-imaging. (B) Ratio of secreted/total proteins at the indicated time points. Data represent mean ± SEM from 4 independent experiments (1-way ANOVA with Dunnett’s multiple comparisons test); **P < 0.01. (C) Pro-collagen, type 1, α-1 (pro-COL1A) concentration in conditioned media of primary fibroblasts determined by enzyme-linked immunosorbent assay. Data represent mean ± SD of quadruplicates (1-way ANOVA with Dunnett’s multiple comparisons test); **P < 0.01, ***P < 0.001. (D) Western blot analyses of LAMP1 and LAMP2 protein species in whole-cell lysates of patient and control fibroblasts. Hypo-glycosylated LAMP1 and LAMP2 proteins in achondrogenesis 1A (ACG1A) and ODCD run at a lower molecular weight range than in controls. (E) Western blot of secreted decorin (DCN) in conditioned supernatants of primary fibroblasts. High-molecular weight species, corresponding to glycanated DCN, include both slower and faster migrating forms in ACG1A and ODCD; different abundance of the core protein indicates a secretory defect. Ponceau S staining of the membrane was used to assess the relative amount of precipitated and transferred total protein.