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

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.

Hyperhomocysteinemia in Cardiovascular Diseases: Revisiting Observational Studies and Clinical Trials

“…25 26 Consistently, CVDs are associated with Hcy-thiolactone and N-Hcy-protein, rather than t-Hcys, 27 and the Hcy-thiolactone/creatinine ratio is a significant predictor of acute myocardial infarction, independent of traditional risk factors and t-Hcy. 28 The serum paraoxonase (PON1) carried by high-density lipoprotein (HDL) protects blood proteins from N-homocysteinylation by hydrolysis of Hcy-thiolactone into Hcy. 29 PON1/HTase activity is associated with CAD risk.…”

Deleterious Effects of Heat Stress on Poultry Production: Unveiling the Benefits of Betaine and Polyphenols

“…One of the important cellular methylation processes is when betaine is involved in the remethylation of homocysteine to eliminate toxic metabolites [43]. Homocysteine is generated by deamination of methionine and is a toxic sulphur-containing intermediate product, and has various consequences for cells, such as oxidative stress, mitochondrial dysfunction, increased cytosolic calcium and protein damage [44], which all contribute to apoptosis [45]. Homocysteine generates ROS and inhibits the expression of antioxidant enzymes which might potentiate the toxic effects of ROS [45].…”

The Effects of Polymorphisms in One-carbon Metabolism Genes on Manifestation of Ichthyosis Vulgaris

“…Our previous research has shown that carriers of FLG 2282del4 mutation, who were heterozygous for C677T polymorphism in the MTHFR gene (1p36.22, OMIM 607093), were 7 times as likely to develop ichthyosis as subjects with wild-type 677CC genotype [15]. It was also found that an elevated plasma homocysteine level impaired not only the metabolism of sulfur-containing amino acids, methionine, and cysteine, but also keratin molecules [16], [17], [18] that might exacerbate the effects of FLG null mutations. Every of single nucleotide polymorphisms (SNPs) of one-carbon metabolism genes -MTHFR C677T (rs1801133) and A1298C (rs1801131), MTR A2756G (rs1805087) and MTRR A66G (rs1801394) -are associated with plasma homocysteine level [19], [20].…”