Guanabenz Interferes with ER Stress and Exerts Protective Effects in Cardiac Myocytes

Abstract

Endoplasmic reticulum (ER) stress has been implicated in a variety of cardiovascular diseases. During ER stress, disruption of the complex of protein phosphatase 1 regulatory subunit 15A and catalytic subunit of protein phosphatase 1 by the small molecule guanabenz (antihypertensive, α2-adrenoceptor agonist) and subsequent inhibition of stress-induced dephosphorylation of eukaryotic translation initiation factor 2α (eIF2α) results in prolonged eIF2α phosphorylation, inhibition of protein synthesis and protection from ER stress. In this study we assessed whether guanabenz protects against ER stress in cardiac myocytes and affects the function of 3 dimensional engineered heart tissue (EHT). We utilized neonatal rat cardiac myocytes for the assessment of cell viability and activation of ER stress-signalling pathways and EHT for functional analysis. (i) Tunicamycin induced ER stress as measured by increased mRNA and protein levels of glucose-regulated protein 78 kDa, P-eIF2α, activating transcription factor 4, C/EBP homologous protein, and cell death. (ii) Guanabenz had no measurable effect alone, but antagonized the effects of tunicamycin on ER stress markers. (iii) Tunicamycin and other known inducers of ER stress (hydrogen peroxide, doxorubicin, thapsigargin) induced cardiac myocyte death, and this was antagonized by guanabenz in a concentration- and time-dependent manner. (iv) ER stressors also induced acute or delayed contractile dysfunction in spontaneously beating EHTs and this was, with the notable exception of relaxation deficits under thapsigargin, not significantly affected by guanabenz. The data confirm that guanabenz interferes with ER stress-signalling and has protective effects on cell survival. Data show for the first time that this concept extends to cardiac myocytes. The modest protection in EHTs points to more complex mechanisms of force regulation in intact functional heart muscle.

Lycopene Protects against Hypoxia/Reoxygenation Injury by Alleviating ER Stress Induced Apoptosis in Neonatal Mouse Cardiomyocytes

“…Despite the established roles of ER stress-induced apoptosis of cardiomyocytes in H/R-injury [ 23 , 24 ], there is no report on the effects of lycopene on ER stress-induced injury in cardiomyocytes. Given the defined role of ER stress and the related pathological conditions of H/R-injury, we propose that in addition to triggering ER stress via disruption of protein proper folding, TG also propagates ER stress, which is supported by both previous reports [ 8 , 48 ] and our findings that TG treatment resulted in an increase in GRP78 and CHOP/GADD153 expression along with the rate of apoptosis. In our current study, we found that TG treatment could decrease the cell viability of cardiomyocytes which was similar to the H/R treatment.…”

Autism-associated R451C mutation in neuroligin3 leads to activation of the unfolded protein response in a PC12 Tet-On inducible system

“…Regulated phosphorylation of eIF2α by the ER stress-activated protein kinase PERK modulates protein synthesis and couples the production of ER client proteins with the organelle's capacity to fold and process them [ 23 ]. Since phosphorylation of eIF2α has been shown to occur soon after ER-stress induction in PC12 cells [ 24 ], we studied PERK activation upon NLGN3 synthesis after 0, 4, 8, 12, 16, 24 and 48 h. We observed that p-eIF2α levels increased over time with a similar trend for the R451C and G221R mutant variants, whereas they remained unaltered for the WT protein ( Figure 4 A, upper panel). The increase in p-eIF2α was detectable after 4 h from NLGN3 induction and reached the highest peak at 12 h, with both mutant variants reaching significantly higher levels over the WT NLGN3 control ( Figure 4 A and Supplementary Figure S2A).…”

Counteracting Protein Kinase Activity in the Heart: The Multiple Roles of Protein Phosphatases

“…As a proof-of-concept specific modulators of PP1 (and PP2A) holoenzymes have been developed not only for the treatment of CVDs but also for the treatment of diabetes, Parkinson’s disease and drug addiction ( Uehata et al, 1997 ; Armstrong et al, 1998 ; McConnell and Wadzinski, 2009 ; Yger and Girault, 2011 ). Concrete examples are disruption of the PP1/GADD34 complex by salubrinal or guanabenz or I-1/I-2 overexpression in rodent/pig models of myocardial infarction ( Boyce et al, 2005 ; Tsaytler et al, 2011 ; Liu et al, 2012 ; Neuber et al, 2014 ). Moreover synthetic peptides containing the PP1c-binding motif (RVxF) have been successfully used to disrupt PP1 complexes in a neuronal and cardiac context, inducing beneficial effects on synaptic transmission and PLB phosphorylation ( Reither et al, 2013 ; Sotoud et al, 2015 ).…”