Both B1R and B2R act as intermediate signaling molecules in high glucose‐induced stimulation of glutamate uptake in ARPE cells

Abstract

Bradykinin (BK) is a potent modulator of biological processes in the retina, and retinal pigment epithelial cells (RPE) and the regulation of glutamate are believed to be important in the pathogenesis of diabetic retinopathy. However, the mechanism by which BK regulates glutamate uptake in RPE cells in diabetic retinopathy is unknown. Here, we examined the involvement of BK receptors in high glucose-induced dysfunction of glutamate uptake in human ARPE cells. High glucose stimulated glutamate uptake and the expression of excitatory amino acid transporter-4 (EAAT4) mRNA, and these were blocked by treatment with small interfering RNA (siRNA) for BK1 receptor (B1R) and BK2 receptor (B2R), but not scrambled siRNA, supporting an involvement of B1R and B2R in this process. High glucose-stimulated glutamate uptake was also blocked by the B1R antagonist [des-Arg(10)]-HOE 140 and the B2R antagonist HOE 140. High glucose increased B1R and B2R mRNA and protein expression in a time-dependent manner, increased B1R and B2R translocation from the cytosol to the nucleus, and stimulated kininogen, kallikrein, and kininase I mRNA expression. We examined whether BK receptors were involved in high glucose-induced signaling pathways. High glucose stimulated arachidonic acid release, cytosolic phospholipase A(2) and cyclooxygenase-2 proteins, nuclear factor-kappaB activation, and inhibitor-kappaB activation; these events were blocked by treatment with B1R and B2R siRNAs, but not scrambled siRNA. In addition, high glucose-induced stimulation of glutamate uptake was blocked by the cyclooxygenase-2 inhibitors arachidonyl trifluoromethyl ketone, mepacrine, 5-bromo-2-(4-fluorophenyl)-3-[4-(methyl-sulfonyl)phenyl]-thiophene, and N-[2-cyclohexyloxy-4-nitrophenyl] methane-sulfonamide, and by the nuclear factor-kappaB inhibitors pyrrolidine dithiocarbamate and SN-50.

The high glucose-induced stimulation of B1R and B2R expression via CB1R activation is involved in rat podocyte apoptosis

“…It remains to be elucidated if phosphorylation of I-κB is not correlated with the reduction of total I-κB protein levels. In a previous report, we showed that the activation of NF-κB acts as an important mediator in BK action under diabetic conditions in human retinal pigment epithelial cells (Lim et al, 2009). We provide here further evidence that the BK-induced activation of NF-κB and I-κB in podocytes may be linked to high glucose-induced apoptosis in diabetic nephropathy.…”

“…Endocannabinoids produce behavioral effects primarily by activating two specific receptors, cannabinoid receptor 1 (CB 1 R) and cannabinoid receptor 2 (CB 2 R). Previously, we demonstrated that KKS activation was involved in the high glucose-induced dysfunction of retinal pigment epithelial cells (Lim et al, 2009). We also demonstrated that CB 1 R activation is involved in high glucose-induced apoptosis in kidney mesangial cells (Lim et al, 2011).…”

Enhanced Ca2+ response and stimulation of prostaglandin release by the bradykinin B2 receptor in human retinal pigment epithelial cells primed with proinflammatory cytokines

“…Overall data support the important role played by BK and kinin receptors in regulating retinal vascular function in both control and diabetic conditions. The present work along with previous studies [15,19,20] also support a role of BK at the outer BRB although further experiments are necessary to evaluate BK-induced RPE dysfunction in vivo.…”

“…BK acts as a mediator of a wide variety of physiological and pathophysiological responses including vasodilation, increased vascular permeability and inflammatory cell recruitment, leading to tissue edema, perpetuation of inflammation and pain. The KKS including mRNAs for kinin B 1 and B 2 receptors is endogenously expressed in human ocular tissues, and a complete system is expressed in human retina and in human RPE [14,15]. In addition, increased levels of components of the KKS have been detected in the vitreous of patients with diabetic retinopathy and in a rat model of carbonic anhydrase-I-induced retinopathy [16] and a role of the KKS in the development of diabetes-induced vascular dysfunction in the retina has been contemplated [17,18].…”

Plasma kallikrein-kinin system and diabetic retinopathy

“…BK has been shown to mediate a variety of activities within neuronal tissues, including stimulating the glutamate release from astrocytes and modulating activities of sensory ion channels (Parpura et al, 1994; Mizumura et al, 2009; Liu et al, 2010a). In addition, both B1R and B2R activation can regulate glutamate clearance by retinal pigmented epithelial cells through a PKC-Akt-COX-2 signaling cascade (Lim et al, 2009). The potential effects of intraocular activation of the KKS on the neuroretina are largely unknown.…”