Increased intracellular proteolysis reduces disease severity in an ER stress–associated dwarfism
Lorna A. Mullan, Ewa J. Mularczyk, Louise H. Kung, Mitra Forouhan, Jordan M.A. Wragg, Royston Goodacre, John F. Bateman, Eileithyia Swanton, Michael D. Briggs, Raymond P. Boot-Handford
Lorna A. Mullan, Ewa J. Mularczyk, Louise H. Kung, Mitra Forouhan, Jordan M.A. Wragg, Royston Goodacre, John F. Bateman, Eileithyia Swanton, Michael D. Briggs, Raymond P. Boot-Handford
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Brief Report Bone biology Development

Increased intracellular proteolysis reduces disease severity in an ER stress–associated dwarfism

Abstract

The short-limbed dwarfism metaphyseal chondrodysplasia type Schmid (MCDS) is linked to mutations in type X collagen, which increase ER stress by inducing misfolding of the mutant protein and subsequently disrupting hypertrophic chondrocyte differentiation. Here, we show that carbamazepine (CBZ), an autophagy-stimulating drug that is clinically approved for the treatment of seizures and bipolar disease, reduced the ER stress induced by 4 different MCDS-causing mutant forms of collagen X in human cell culture. Depending on the nature of the mutation, CBZ application stimulated proteolysis of misfolded collagen X by either autophagy or proteasomal degradation, thereby reducing intracellular accumulation of mutant collagen. In MCDS mice expressing the Col10a1.pN617K mutation, CBZ reduced the MCDS-associated expansion of the growth plate hypertrophic zone, attenuated enhanced expression of ER stress markers such as Bip and Atf4, increased bone growth, and reduced skeletal dysplasia. CBZ produced these beneficial effects by reducing the MCDS-associated abnormalities in hypertrophic chondrocyte differentiation. Stimulation of intracellular proteolysis using CBZ treatment may therefore be a clinically viable way of treating the ER stress–associated dwarfism MCDS.

Authors

Lorna A. Mullan, Ewa J. Mularczyk, Louise H. Kung, Mitra Forouhan, Jordan M.A. Wragg, Royston Goodacre, John F. Bateman, Eileithyia Swanton, Michael D. Briggs, Raymond P. Boot-Handford

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Figure 2

Effect of CBZ on the growth plate pathology associated with MCDS.

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Effect of CBZ on the growth plate pathology associated with MCDS. Three-...
Three-week-old MCDS mice were treated with CBZ for a period of 1 week. Untreated MCDS mice and mice WT for collagen X were used as controls. (A) H&E staining of the tibial growth plate and immunohistochemistry for (B) collagen X and (C) Bip/Grp78. Brackets indicate the hypertrophic zone. Scale bars: 100 μM. (D) Hypertrophic zone measurements at 4 weeks of age. Mean ± SEM. MCDS vs MCDS CBZ *P < 0.05. (E) Typical Western blots of rib growth plate cartilage extracts at 4 weeks of age for Bip and Atf4 alongside their Coomassie blue–stained protein loading control gel (F). (G and H) Quantification of BiP and Atf4 (n = 3 independent analyses). (I) X-ray images of pelvis illustrating the distortion of the ischial tuberosity in MCDS mice at 6 weeks of age. (J) The angle between the lines was measured for each group (mean ± SEM, n = 5). Bone growth expressed as percentage of increase based on length at 3 weeks of age in each animal for (K) tibia and (L) femur. Mean ± SEM. n = 6 MCDS mice and n = 7 MCDS CBZ-treated mice. *P < 0.05; **P < 0.005; ***P < 0.0005. All statistical analyses by ANOVA.