Increased Dicarbonyl Metabolism in Endothelial Cells in Hyperglycemia Induces Anoikis and Impairs Angiogenesis by RGD and GFOGER Motif Modification

Abstract

Chronic vascular disease in diabetes isC hronic vascular disease is the major cause of morbidity and mortality in diabetes (1). This is associated with dysfunction of endothelial cells in hyperglycemia (2) and damage to the endothelium; the latter is indicated in vivo by increased detachment and premature death of endothelial cells by apoptosis (including anoikis) (3,4). A cellular marker of damage to the endothelium, increased number of circulating endothelial cells, in diabetes was not linked directly to glycemic control (HbA 1c [A1C]) (5). Extracellular matrix (ECM) interactions with endothelial cells maintain cell survival (6) and support angiogenesis driven by vascular endothelial-derived growth factor and other angiogenic factors (7). Early stages of microangiopathy and wound healing are characterized by development of acellular capillaries and decreased angiogenesis with consequent ischemia (8). A metabolic link to ECM disengagement of endothelial cells and impaired angiogenesis has not been identified.Most cell adhesion and signaling occur via integrins, which mediate a variety of cell-cell and cell-matrix interactions. The ␣ 1 ␤ 1 and ␣ 2 ␤ 1 integrins recognize the GFOGER sequence found in collagens (9,10) (Fig. 1A). Several integrins recognize the RGD sequence within ECM proteins (6,11) where the RGD moiety binds astride the integrin ␣-and ␤-subunits with the Arg residue making electrostatic interaction with one or two Asp residues of the ␣-subunit (12,13).Methylglyoxal is a potent arginine-directed glycating agent formed mainly by the degradation of triosephosphates (14,15) with increased flux of formation in hyperglycemia associated with diabetes (16). It reacts with arginine residues to form a hydroimidazolone derivative, N␦-(5-hydro-5-methyl-4-imidazolon-2-yl)-ornithine (MG-H1)residues, an advanced glycation end product (AGE) (17,18), with loss of associated side chain positive charge (19) (Fig. 1B). MG-H1 residues are a major type of protein damage by glycation in diabetes, occurring on both cellular and extracellular proteins (20,21). Increased concentration of MG-H1 residues in plasma protein of diabetic patients was not linked directly to A1C (22), probably because methylglyoxal formation is increased in both fasting and postprandial hyperglycemia (16,23) and influenced by factors other than hyperglycemia (low glyceraldehyde-3-phosphate dehydrogenase activity [24]). MG-H1 residue formation occurred at susceptible hotspot sites in proteins with loss of functional activity (19). The surface sheath network of type IV collagen in blood vessels (25) binds integrins of vascular endothelial cells, anchoring and sustaining the vascular endothelium by interaction with integrins at GFOGER and RGD sites of the triple helical domain (9,26). These integrin binding sites are potential targets for methylglyoxal modification.We report here that modification by methylglyoxal of GFOGER and RGD sites in type IV collagen in hyperglycemia impairs ECM attachment, viability, and angiogenic activity of endothelial ce...

Increased protein damage in renal glomeruli, retina, nerve, plasma and urine and its prevention by thiamine and benfotiamine therapy in a rat model of diabetes

“…Other studies have found degeneration of sciatic nerve and retina characteristic of early-stage diabetic neuropathy and retinopathy in this model [14,15]. Increased tissue content of AGEs in diabetes leads to impairment of protein function, linked to vascular cell detachment and anoikis [16,17], oxidative stress [18], low-grade inflammation [18,19] and other cell dysfunctions implicated in the development of microvascular complications [20]. Thiamine and benfotiamine proba- Data are means±SD; units are mmol/mol lysine for FL, CML and CEL and mmol/mol arginine for G-H1, MG-H1 and 3DG-H Rat study group key as in Table 1 *p<0.05, **p<0.01 and ***p<0.001 with respect to normal control † p<0.05, † † p<0.01 † † † p<0.001 with respect to diabetic controls bly decrease AGE and oxidation and nitration adduct formation by increasing transketolase expression and activity in tissues [3,4,21]; this counters metabolic dysfunction and oxidative stress in hyperglycaemia, maintains antioxidant and dicarbonyl-metabolising enzyme activities and thereby prevents protein damage [2].…”

Morphological changes induced by advanced glycation endproducts in osteoblastic cells: Effects of co-incubation with alendronate

“…The interruption of this connection to the ECM has detrimental effects on cell survival, leading to a specific type of apoptosis called anoikis in most non-transformed cell types (Reddig and Juliano, 2005). Dobler et al (2006) recently reported that the chronic vascular disease of diabetes is associated with a disruption of endothelial cell adhesion to its ECM, endangering cell survival and vascular structure. The authors show that methylglyoxal, a precursor of AGEs whose formation is increased in hyperglycemia, causes a strong change in the binding sites of integrins to type IV collagen of the vascular basement membrane, causing endothelial cell detachment, anoikis, and inhibition of angiogenesis.…”

Anoikis: an emerging hallmark in health and diseases

“…Indeed, in diabetic patients the early stages of microangiopathy is characterized by the development of acellular capillaries and decreased angiogenesis with consequent ischaemia [158]. Interestingly, Dobler reported that methylglyoxal, a dicarbonyl glycating agent whose formation is improved in hyperglycaemia, provokes strong modifications in integrin-binding sites of type IV collagen within the vascular basement membrane, causing detachment and anoikis of endothelial cells [159,160]. Thus, increased formation of methylglyoxal and ECM glycation in hyperglycaemia impairs endothelial cell survival and vasculature structure and inhibits angiogenesis, likely contributing to vascular dysfunction in diabetes [159].…”

“…Interestingly, Dobler reported that methylglyoxal, a dicarbonyl glycating agent whose formation is improved in hyperglycaemia, provokes strong modifications in integrin-binding sites of type IV collagen within the vascular basement membrane, causing detachment and anoikis of endothelial cells [159,160]. Thus, increased formation of methylglyoxal and ECM glycation in hyperglycaemia impairs endothelial cell survival and vasculature structure and inhibits angiogenesis, likely contributing to vascular dysfunction in diabetes [159]. Emerging therapeutic interventions aimed at scavenging methylglyoxal prevent the loss of endothelial cells and the impairment of angiogenesis, ultimately inhibiting the vascular complications of diabetes.…”