Tysnd1 Deficiency in Mice Interferes with the Peroxisomal Localization of PTS2 Enzymes, Causing Lipid Metabolic Abnormalities and Male Infertility

Chizuru Ito,Fowzan S Alkuraya,Hiroshi Hara,Mohan V Jacob ,Taro Okazaki ,Ali Al‐Odaib ,Mioko Iseki,Mitsuhiro Watanabe,Yuichi Ninomiya,Christian Schönbach,Tohru Tsukui,Masumi Akita,Yasushi Horai,Ryouta Maeba,Mohammed Al Amoudi,Yasushi Okazaki,Yumi Mizuno,Yosuke Mizuno,Tetsuo Noda,Hiroyasu Iwasa,Yutaka Nakachi,Megumi Nishimukai,Nobuyuki Shimozawa,Kiyotaka Toshimori,Shigeharu Wakana,Hiromi Motegi,Igor V Kurochkin

doi:10.1371/journal.pgen.1003286

Abstract

Peroxisomes are subcellular organelles involved in lipid metabolic processes, including those of very-long-chain fatty acids and branched-chain fatty acids, among others. Peroxisome matrix proteins are synthesized in the cytoplasm. Targeting signals (PTS or peroxisomal targeting signal) at the C-terminus (PTS1) or N-terminus (PTS2) of peroxisomal matrix proteins mediate their import into the organelle. In the case of PTS2-containing proteins, the PTS2 signal is cleaved from the protein when transported into peroxisomes. The functional mechanism of PTS2 processing, however, is poorly understood. Previously we identified Tysnd1 (Trypsin domain containing 1) and biochemically characterized it as a peroxisomal cysteine endopeptidase that directly processes PTS2-containing prethiolase Acaa1 and PTS1-containing Acox1, Hsd17b4, and ScpX. The latter three enzymes are crucial components of the very-long-chain fatty acids β-oxidation pathway. To clarify the in vivo functions and physiological role of Tysnd1, we analyzed the phenotype of Tysnd1−/− mice. Male Tysnd1−/− mice are infertile, and the epididymal sperms lack the acrosomal cap. These phenotypic features are most likely the result of changes in the molecular species composition of choline and ethanolamine plasmalogens. Tysnd1−/− mice also developed liver dysfunctions when the phytanic acid precursor phytol was orally administered. Phyh and Agps are known PTS2-containing proteins, but were identified as novel Tysnd1 substrates. Loss of Tysnd1 interferes with the peroxisomal localization of Acaa1, Phyh, and Agps, which might cause the mild Zellweger syndrome spectrum-resembling phenotypes. Our data established that peroxisomal processing protease Tysnd1 is necessary to mediate the physiological functions of PTS2-containing substrates.

Highlights

Peroxisomes are subcellular organelles that are involved in the catabolism of very-long-chain fatty acids (VLCFAs), branchedchain fatty acids, D-amino acids, polyamines and the biosynthesis of bile acids [1,2,3]
Peroxisomes are subcellular organelles that are present in almost all eukaryotic cells
In an earlier study we identified a protease named Tysnd1 that is located in the peroxisomes and processes the enzymes catalyzing the peroxisomal boxidation of very-long-chain fatty acids

Summary

Introduction

Peroxisomes are subcellular organelles that are involved in the catabolism of very-long-chain fatty acids (VLCFAs), branchedchain fatty acids, D-amino acids, polyamines and the biosynthesis of bile acids [1,2,3]. Abnormalities of peroxisomal biogenesis or enzymes cause dysfunctions of the peroxisomal metabolism [3]. Peroxisomal disorders are divided into two large groups: Zellweger Syndrome spectrum (ZSS) and deficiency of peroxisomal enzymes [3]. ZSS is caused by defects of PEX (peroxisomal biogenesis factor) gene family members that interfere with or abrogate the biogenesis resulting in abnormally shaped peroxisomes or peroxisome deficiency [3,4,5]. ZSS includes neonatal adrenoleukodystrophy, infantile Refsum disease, rhizomelic chondrodysplasia punctata (RCDP) type 1 and Zellweger syndrome, the most severe form [3]. RCDP type 1 disease is caused by mutations in PEX7 that interfere with its function as a receptor in targeting PTS2-containing proteins ACAA1 (acetyl-CoA acyltransferase 1), AGPS (alkylglycerone phosphate synthase) and PHYH (phytanoyl-CoA 2-hydroxylase) to the peroxisomes. The mutated PEX7-mediated effects result in the accumulation of VLCFAs, phytanic acid and a reduced plasmalogen synthesis [8]

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Discussion

Conclusion