Mutations in Homocysteine Metabolism Genes Increase Keratin N-Homocysteinylation and Damage in Mice.

Kamila Borowczyk,Isao Ishii,Hieronim Jakubowski,Noriyuki Akahoshi,Joanna Suliburska,Jacek Wróblewski

doi:10.1155/2018/7570850

Abstract

Genetic or nutritional deficiencies in homocysteine (Hcy) metabolism increase Hcy-thiolactone, which causes protein damage by forming isopetide bonds with lysine residues, generating N-Hcy-protein. In the present work, we studied the prevalence and genetic determinants of keratin damage caused by homocysteinylation. We found that in mammals and birds, 35 to 98% of Hcy was bound to hair keratin via amide or isopeptide bond (Hcy-keratin), while 2 to 65% was S-Hcy-keratin. A major fraction of hair Hcy-keratin (56% to 93%), significantly higher in birds than in mammals, was sodium dodecyl sulfate-insoluble. Genetic hyperhomocysteinemia significantly increased N-Hcy-keratin levels in the mouse pelage. N-Hcy-keratin was elevated 3.5-, 6.3-, and 11.7-fold in hair from Mthfr−/−, Cse−/−, or Cbs−/− mice, respectively. The accumulation of N-Hcy in hair keratin led to a progressive reduction of N-Hcy-keratin solubility in sodium dodecyl sulfate, from 0.39 ± 0.04 in wild-type mice to 0.19 ± 0.03, 0.14 ± 0.01, and 0.07 ± 0.03 in Mthfr−/−, Cse−/−, or Cbs−/−animals, respectively. N-Hcy-keratin accelerated aggregation of unmodified keratin in Cbs−/− mouse hair. Keratin methionine, copper, and iron levels in mouse hair were not affected by hyperhomocysteinemia. These findings provide evidence that pelage keratin is N-homocysteinylated in vivo in mammals and birds, and that this process causes keratin damage, manifested by a reduced solubility.

Highlights

Homocysteine (Hcy) is an important intermediate in folate and one-carbon metabolism
We found that both Hcy-keratin and S-Hcy-keratin were present both in mammal and bird pelages at levels ranging from 56 to 733 pmol/mg hair (Table 1)
The present work shows that Hcy-keratin is highly prevalent in a variety of mammal and bird species

Summary

Introduction

Homocysteine (Hcy) is an important intermediate in folate and one-carbon metabolism. The only known source of Hcy in our body is the essential dietary protein amino acid methionine (Met). Genetic or nutritional deficiencies in folate/one-carbon metabolism lead to the hyperhomocysteinemia (HHcy) and are known to cause abnormalities in many organs, including the cardiovascular system and the brain [1]. Hcy is metabolized to the thioester Hcy-thiolactone in an error-editing reaction in protein biosynthesis when Hcy is erroneously selected in place of Met by methionyltRNA synthetase [2]. Because Hcy-thiolactone is chemically reactive, it modifies ε-amino groups of protein lysine residues, which generates N-homocysteinylated protein (NHcy-protein) [2]. N-Homocysteinylation is an emerging posttranslational protein modification [3] that impairs or International Journal of Genomics alters the protein’s structure/function, causes protein damage in vitro [2, 4] and in vivo [5,6,7], generates amyloid-like structures [2, 8, 9], and induces proatherogenic changes in gene expression [10], an autoimmune response [2, 11], and atherothrombosis [2, 12, 13]

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Conclusion