Palmitoyl Acyltransferase, Zdhhc13, Facilitates Bone Mass Acquisition by Regulating Postnatal Epiphyseal Development and Endochondral Ossification: A Mouse Model

I-Wen Song,Jer-Yuarn Wu,Wei-Ru Li,Yu-Ju Chen,Virginia Byers Kraus,Kai-Ming Liu,Yuan-Tsong Chen,Yi-Ju Chen,Li-Fen Shen,M T Michael Lee,Jeffrey J Y Yen,Li-Ying Chen,Damian Christopher Genetos

doi:10.1371/journal.pone.0092194

Abstract

ZDHHC13 is a member of DHHC-containing palmitoyl acyltransferases (PATs) family of enzymes. It functions by post-translationally adding 16-carbon palmitate to proteins through a thioester linkage. We have previously shown that mice carrying a recessive Zdhhc13 nonsense mutation causing a Zdhcc13 deficiency develop alopecia, amyloidosis and osteoporosis. Our goal was to investigate the pathogenic mechanism of osteoporosis in the context of this mutation in mice. Body size, skeletal structure and trabecular bone were similar in Zdhhc13 WT and mutant mice at birth. Growth retardation and delayed secondary ossification center formation were first observed at day 10 and at 4 weeks of age, disorganization in growth plate structure and osteoporosis became evident in mutant mice. Serial microCT from 4-20 week-olds revealed that Zdhhc13 mutant mice had reduced bone mineral density. Through co-immunoprecipitation and acyl-biotin exchange, MT1-MMP was identified as a direct substrate of ZDHHC13. In cells, reduction of MT1-MMP palmitoylation affected its subcellular distribution and was associated with decreased VEGF and osteocalcin expression in chondrocytes and osteoblasts. In Zdhhc13 mutant mice epiphysis where MT1-MMP was under palmitoylated, VEGF in hypertrophic chondrocytes and osteocalcin at the cartilage-bone interface were reduced based on immunohistochemical analyses. Our results suggest that Zdhhc13 is a novel regulator of postnatal skeletal development and bone mass acquisition. To our knowledge, these are the first data to suggest that ZDHHC13-mediated MT1-MMP palmitoylation is a key modulator of bone homeostasis. These data may provide novel insights into the role of palmitoylation in the pathogenesis of human osteoporosis.

Highlights

Palmitoylation is a post-translational lipid modification involving the addition of a 16-carbon palmitate on specific cysteine residues of proteins through a thioester linkage [1]
4 mouse models have been generated: Zdhhc5 gene-trap mice show a reduction in contextual fear [12]; Zdhhc8 knockout mice manifest a schizophrenia phenotype [13]; mice with a F233 deletion in Zdhhc21 show abnormalities of skin homeostasis and hair defects [14]; and as described in our previous report, a nonsense mutation was generated in the Zdhhc13 gene by ENU mutagenesis
We previously reported that Zdhhc13 deficient mutant mice had severe osteoporosis at 26 weeks of age [15]

Summary

Introduction

Palmitoylation is a post-translational lipid modification involving the addition of a 16-carbon palmitate on specific cysteine residues of proteins through a thioester linkage [1]. 4 mouse models have been generated: Zdhhc gene-trap mice show a reduction in contextual fear [12]; Zdhhc knockout mice manifest a schizophrenia phenotype [13]; mice with a F233 deletion in Zdhhc show abnormalities of skin homeostasis and hair defects [14]; and as described in our previous report, a nonsense mutation was generated in the Zdhhc gene by ENU mutagenesis. This mutation resulted in nonsense mediated mRNA decay of Zdhhc mRNA. The detailed pathogenic mechanisms of all these phenotypes still remain unclear

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