The Maillard or non-enzymatic glycosylation reaction is the reaction which occurs between reducing sugars and proteins. It leads to the formation of protein adducts and crosslinks thought to be responsible for age- and diabetes-related stiffening of collagen-rich tissues. With previous funding from the National Institute on Aging, our laboratory has contributed toward establishing the structure of the first fluorescent cross- link of the Maillard reaction in vivo, the role of pyrroles in protein aging by glucose, the biological significance of glycoxidation in aging and age- related diseases, especially diabetes and end stage renal disease, and the relationship between glycation, glycoxidation and longevity. Finally, our laboratory has discovered, characterized and cloned deglycating enzymes (Amadoriases) from soil organisms. These data, together with those from other laboratories, now implicate a strong link between the formation of advanced of advanced Maillard products (AGEs), metabolic pathways along the glucose axis, and age- related crosslinking of collagen. However, whereas a general picture is now emerging, it is unclear why, e.g., dog collagen is becoming crosslinked at much higher rate than human collagen, and which crosslinks are important in dictating the physical-chemical properties of the aging extracellular matrix.
In Specific Aim 1 (part 1), we hypothesize that non-UV active and/or labile crosslinks must be forming during the advanced Maillard reaction which comprise besides lys-lys, also lys-arg and arg-arg crosslinks. Some of these may involve amide and amidine bonds whereby dicarbonyl compounds are expected to play major roles in their formation. In part 2 of Specific Aim 1 we will initiate research into the role of the non- oxidative pathway, so called 2,3-enolization pathway of the Maillard reaction in crosslink formation and develop specific probe for its occurrence in vivo.
In Specific Aim 2, we will collaborate with Dr. Julie Kornfield's group at Caltech and attempt to identify the crosslinks that are most determinant in dictating the physical-chemical properties of collagen in the reaction initiated by glyceraldehyde.
In Specific Aim 3, we will identify the nature and sites of crosslinks that are responsible for the accelerated crosslinking in the glyceraldehyde (Specific Aim 2) and the dog model of accelerated aging. We will also investigate the potential role of ornithine as a novel crosslinking amino acid in aging human collagen. Our approach, we expect, will result in the first comprehensive, hierarchical map of collagen crosslinks that for, during aging.
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