Kyle L. Brown, Carl Darris, Kristie Lindsey Rose, Otto A. Sanchez, Hartman Madu, Josh Avance, Nickolas Brooks, Ming-Zhi Zhang, Agnes Fogo, Raymond Harris, Billy G. Hudson and Paul Voziyan
In diabetes, toxic oxidative pathways are triggered by persistent hyperglycemia and contribute to diabetic complications. A major proposed pathogenic mechanism is accumulation of protein modifications called advanced glycation end products (AGEs). However, other non-enzymatic post-translational modifications may also contribute to pathogenic protein damage in diabetes. We demonstrate that hypohalous acid-derived modifications of renal tissues and extracellular matrix (ECM) proteins are significantly elevated in experimental diabetic nephropathy. Moreover, diabetic renal ECM shows diminished binding of α1β1 integrin consistent with modification of collagen IV by hypochlorous (HOCl) and hypobromous (HOBr) acids. NC1 hexamers, key connection modules of collagen IV networks, are modified via oxidation and chlorination of tryptophan and bromination of tyrosine residues. Chlorotryptophan, a relatively minor modification, has not been previously found in proteins. In the NC1 hexamers isolated from diabetic kidneys, levels of HOCl-derived oxidized and chlorinated tryptophan residues W28 and W192 are significantly elevated compared to non-diabetic controls. Molecular dynamics simulations predicted more relaxed NC1 hexamer tertiary structure and diminished assembly competence in diabetes; this was confirmed using limited proteolysis and denaturation/refolding. Our results suggest that hypohalous acid-derived modifications of renal ECM and specifically collagen IV networks contribute to functional protein damage in diabetes.