RESUMEN
Protease-activated receptor (PAR)4 is a low affinity thrombin receptor with less understood function relative to PAR1. PAR4 is involved in platelet activation and hemostasis, but its specific actions on myocyte growth and cardiac function remain unknown. This study examined the role of PAR4 deficiency on cardioprotection after myocardial ischemia-reperfusion (IR) injury in mice. When challenged by in vivo or ex vivo IR, PAR4 knockout (KO) mice exhibited increased tolerance to injury, which was manifest as reduced infarct size and a more robust functional recovery compared to wild-type mice. PAR4 KO mice also showed reduced cardiomyocyte apoptosis and putative signaling shifts in survival pathways in response to IR. Inhibition of PAR4 expression in isolated cardiomyocytes by shRNA offered protection against thrombin and PAR4-agonist peptide-induced apoptosis, while overexpression of wild-type PAR4 significantly enhanced the susceptibility of cardiomyocytes to apoptosis, even under low thrombin concentrations. Further studies implicate Src- and epidermal growth factor receptor-dependent activation of JNK on the proapoptotic effect of PAR4 in cardiomyocytes. These findings reveal a pivotal role for PAR4 as a regulator of cardiomyocyte survival and point to PAR4 inhibition as a therapeutic target offering cardioprotection after acute IR injury.
Asunto(s)
Daño por Reperfusión Miocárdica/genética , Miocardio/metabolismo , Miocitos Cardíacos/metabolismo , Receptores de Trombina/genética , Animales , Apoptosis/genética , Receptores ErbB/genética , Receptores ErbB/metabolismo , Regulación de la Expresión Génica , MAP Quinasa Quinasa 4/genética , MAP Quinasa Quinasa 4/metabolismo , Masculino , Ratones , Ratones Noqueados , Daño por Reperfusión Miocárdica/metabolismo , Daño por Reperfusión Miocárdica/patología , Miocardio/patología , Miocitos Cardíacos/efectos de los fármacos , Miocitos Cardíacos/patología , Péptidos/farmacología , Cultivo Primario de Células , ARN Interferente Pequeño/genética , ARN Interferente Pequeño/metabolismo , Receptores de Trombina/agonistas , Receptores de Trombina/antagonistas & inhibidores , Receptores de Trombina/deficiencia , Transducción de Señal , Trombina/farmacología , Familia-src Quinasas/genética , Familia-src Quinasas/metabolismoRESUMEN
End organ injury in diabetes mellitus (DM) is driven by microvascular compromise (including diabetic retinopathy and nephropathy). Cognitive impairment is a well-known complication of DM types 1 and 2; however, its mechanism(s) is(are) not known. We hypothesized that blood-brain barrier (BBB) compromise plays a key role in cognitive decline in DM. Using a DM type 1 model (streptozotocin injected C57BL/6 mice) and type 2 model (leptin knockout obese db/db mice), we showed enhanced BBB permeability and memory loss (Y maze, water maze) that are associated with hyperglycemia. Gene profiling in isolated microvessels from DM type 1 animals demonstrated deregulated expression of 54 genes related to angiogenesis, inflammation, vasoconstriction/vasodilation, and platelet activation pathways by at least 2-fold (including eNOS, TNFα, TGFß1, VCAM-1, E-selectin, several chemokines, and MMP9). Further, the magnitude of gene expression was linked to degree of cognitive decline in DM type 1 animals. Gene analysis in brain microvessels of DM type 2 db/db animals showed alterations of similar genes as in DM 1 model, some to an even greater extent. Neuropathologic analyses of brain tissue derived from DM mice showed microglial activation, expression of ICAM-1, and attenuated coverage of pericytes compared to controls. There was a significant upregulation of inflammatory genes in brain tissue in both DM models. Taken together, our findings indicate that BBB compromise in DM in vivo models and its association with memory deficits, gene alterations in brain endothelium, and neuroinflammation. Prevention of BBB injury may be a new therapeutic approach to prevent cognitive demise in DM.