N‐Homocysteinylation impairs collagen cross‐linking in cystathionine β‐synthase‐deficient mice: a novel mechanism of connective tissue abnormalities

Abstract

Cystathionine β-synthase (CBS) deficiency, a genetic disorder in homocysteine (Hcy) metabolism in humans, elevates plasma Hcy-thiolactone and leads to connective tissue abnormalities that affect the cardiovascular and skeletal systems. However, the underlying mechanism of these abnormalities is not understood. Hcy-thiolactone has the ability to form isopeptide bonds with protein lysine residues, which generates N-homocysteinylated protein. Because lysine residues are involved in collagen cross-linking, N-homocysteinylation of these lysines should impair cross-linking. Using a Tg-I278T Cbs mouse model of hyperhomocysteinemia (HHcy) which replicates the connective tissue abnormalities observed in CBS-deficient patients, we found that N-Hcy-collagen was elevated in bone, tail, and heart of Cbs mice, whereas pyridinoline cross-links were significantly reduced. Plasma deoxypyridinoline cross-link and cross-linked carboxyterminal telopeptide of type I collagen were also significantly reduced in the Cbs mice. Lysine oxidase activity and mRNA level were not reduced by the Cbs genotype. We also showed that collagen carries S-linked Hcy bound to the thiol of N-linked Hcy. In vitro experiments showed that Hcy-thiolactone modifies lysine residues in collagen type I α-1 chain. Residue K, located in the nonhelical N-telopeptide region and involved in pyridinoline cross-link formation, was also N-homocysteinylated in vivo Taken together, our findings showed that N-homocysteinylation of collagen in Cbs mice impairs its cross-linking. These findings explain, at least in part, connective tissue abnormalities observed in HHcy.-Perła-Kajan, J., Utyro, O., Rusek, M., Malinowska, A., Sitkiewicz, E., Jakubowski, H. N-Homocysteinylation impairs collagen cross-linking in cystathionine β-synthase-deficient mice: a novel mechanism of connective tissue abnormalities.

Urinary excretion of homocysteine thiolactone and the risk of acute myocardial infarction in coronary artery disease patients: the WENBIT trial

“…Animal studies show that N ‐Hcy‐protein accumulates within atherosclerotic lesions in aortas of ApoE −/− mice fed with a normal chow diet and that the accumulation increases in the ApoE −/− animals fed with a HHcy diet‐. Other data show that N ‐homocysteinylation impairs collagen cross‐linking in various organs, including the heart, of Cbs −/− mice, thus providing an explanation for connective tissue deficiencies prevalent in HHcy humans . In small, case–control studies, elevated plasma Hcy‐thiolactone and N ‐Hcy‐protein are associated with vascular damage in diabetes and increased CAD risk , respectively.…”

Enzyme replacement therapy prevents loss of bone and fat mass in murine homocystinuria

“…Collagen is a major extracellular matrix component of bone providing structural support coming from specific cross‐links involving lysine residues within and between collagen chains (Boskey, ). N‐homocysteinylation of these lysines was hypothesized to impair cross‐linking (Jackson, ; Lubec, Fang‐Kircher, Lubec, Blom, & Boers, ), but only recently proven in I278T mice (Perla‐Kajan et al., ), thus at least partially explaining skeletal and connective tissue defects in HCU. The study comparing Tg‐WT and I278T mice showed that, while the amount of bound Hcy to plasma proteins is similar, the amount of total free Hcy (i.e., sum of free reduced Hcy and Hcy from Hcy–Hcy and Hcy–Cys disulfides) was significantly higher in I278T mice suggesting that plasma proteins have a maximum binding capacity for Hcy (Gupta et al., ).…”

Vitamin B12 and Semen Quality

“…In this reaction, homocysteine thiolactone, an active cyclic thioester in which the carboxyl group is condensed with the sulfhydryl group, acylates the free amino groups of protein lysine residues [57]. The integration of homocysteine molecules with any given protein may significantly affect its functional domain, and therefore the entire protein function [58]. …”