RESUMO
CONTEXT: Molecular pathogenesis of chronic alcoholism is linked to increased endoplasmic reticulum stress. Ethanol is a competitive inhibitor of vitamin A metabolism and vitamin A supplementation aggravates existing liver problems. Hence, we probed into the impact of supplementation of all trans retinoic acid (ATRA), the active metabolite of vitamin A on ethanol-induced endoplasmic reticulcum stress. METHODS: Male Sprague-Dawley rats were divided into four groups - I: Control; II: Ethanol; III: ATRA; IV: ATRA + Ethanol. After 90 days the animals were sacrificed to study markers of lipid peroxidation in hepatic microsomal fraction and expression of ER stress proteins and apoptosis in liver. RESULTS AND CONCLUSION: Ethanol caused hepatic hyperlipidemia, enhanced microsomal lipid peroxidation, upregulated expression of unfolded protein response associated proteins and that of apoptosis. Ethanol also led to downregulation of retinoid receptors. ATRA supplementation reversed all these alterations indicating the decrease in ethanol-induced endoplasmic reticulum stress.
Assuntos
Suplementos Nutricionais , Estresse do Retículo Endoplasmático , Fígado Gorduroso Alcoólico/prevenção & controle , Fígado/metabolismo , Substâncias Protetoras/uso terapêutico , Receptores do Ácido Retinoico/agonistas , Tretinoína/uso terapêutico , Fator 4 Ativador da Transcrição/agonistas , Fator 4 Ativador da Transcrição/antagonistas & inibidores , Fator 4 Ativador da Transcrição/genética , Fator 4 Ativador da Transcrição/metabolismo , Animais , Apoptose/efeitos dos fármacos , Biomarcadores/metabolismo , Citocromo P-450 CYP2E1/química , Citocromo P-450 CYP2E1/genética , Citocromo P-450 CYP2E1/metabolismo , Estresse do Retículo Endoplasmático/efeitos dos fármacos , Etanol/toxicidade , Fígado Gorduroso Alcoólico/enzimologia , Fígado Gorduroso Alcoólico/metabolismo , Regulação da Expressão Gênica/efeitos dos fármacos , Metabolismo dos Lipídeos/efeitos dos fármacos , Peroxidação de Lipídeos/efeitos dos fármacos , Fígado/efeitos dos fármacos , Fígado/enzimologia , Masculino , Ratos Sprague-Dawley , Receptores do Ácido Retinoico/antagonistas & inibidores , Receptores do Ácido Retinoico/genética , Receptores do Ácido Retinoico/metabolismo , Receptores X de Retinoides/agonistas , Receptores X de Retinoides/antagonistas & inibidores , Receptores X de Retinoides/genética , Receptores X de Retinoides/metabolismo , Fator de Transcrição CHOP/agonistas , Fator de Transcrição CHOP/antagonistas & inibidores , Fator de Transcrição CHOP/genética , Fator de Transcrição CHOP/metabolismo , Tretinoína/antagonistas & inibidores , Resposta a Proteínas não Dobradas/efeitos dos fármacos , Proteína 1 de Ligação a X-Box/agonistas , Proteína 1 de Ligação a X-Box/antagonistas & inibidores , Proteína 1 de Ligação a X-Box/genética , Proteína 1 de Ligação a X-Box/metabolismoRESUMO
Ventilator-induced lung injury (VILI) is a severe complication of mechanical ventilation that can lead to acute respiratory distress syndrome. VILI is characterized by damage to the epithelial barrier with subsequent pulmonary edema and profound hypoxia. Available lung-protective ventilator strategies offer only a modest benefit in preventing VILI because they cannot impede alveolar overdistension and concomitant epithelial barrier dysfunction in the inflamed lung regions. There are currently no effective biochemical therapies to mitigate injury to the alveolar epithelium. We hypothesize that alveolar stretch activates the integrated stress response (ISR) pathway and that the chemical inhibition of this pathway mitigates alveolar barrier disruption during stretch and mechanical ventilation. Using our established rat primary type I-like alveolar epithelial cell monolayer stretch model and in vivo rat mechanical ventilation that mimics the alveolar overdistension seen in acute respiratory distress syndrome, we studied epithelial responses to mechanical stress. Our studies revealed that the ISR signaling pathway is a key modulator of epithelial permeability. We show that prolonged epithelial stretch and injurious mechanical ventilation activate the ISR, leading to increased alveolar permeability, cell death, and proinflammatory signaling. Chemical inhibition of protein kinase RNA-like endoplasmic reticulum kinase, an upstream regulator of the pathway, resulted in decreased injury signaling and improved barrier function after prolonged cyclic stretch and injurious mechanical ventilation. Our results provide new evidence that therapeutic targeting of the ISR can mitigate VILI.
Assuntos
Células Epiteliais Alveolares/patologia , Estresse Fisiológico/fisiologia , Lesão Pulmonar Induzida por Ventilação Mecânica/fisiopatologia , Fator 4 Ativador da Transcrição/antagonistas & inibidores , Fator 4 Ativador da Transcrição/genética , Fator 4 Ativador da Transcrição/fisiologia , Adenina/análogos & derivados , Adenina/farmacologia , Adenina/uso terapêutico , Células Epiteliais Alveolares/metabolismo , Animais , Morte Celular , Permeabilidade da Membrana Celular , Células Cultivadas , Citocinas/metabolismo , Avaliação Pré-Clínica de Medicamentos , Ativação Enzimática , Regulação da Expressão Gênica , Indóis/farmacologia , Indóis/uso terapêutico , Inibidores de Proteases/farmacologia , Inibidores de Proteases/uso terapêutico , Edema Pulmonar/tratamento farmacológico , Edema Pulmonar/etiologia , Interferência de RNA , Ratos , Ratos Sprague-Dawley , Transdução de Sinais , Estresse Mecânico , Fator de Transcrição CHOP/antagonistas & inibidores , Fator de Transcrição CHOP/genética , Fator de Transcrição CHOP/fisiologia , Resposta a Proteínas não Dobradas , eIF-2 Quinase/antagonistas & inibidores , eIF-2 Quinase/genética , eIF-2 Quinase/fisiologiaRESUMO
The transcription factor ATF4 regulates the expression of genes involved in amino acid metabolism, redox homeostasis and ER stress responses, and it is overexpressed in human solid tumours, suggesting that it has an important function in tumour progression. Here, we report that inhibition of ATF4 expression blocked proliferation and survival of transformed cells, despite an initial activation of cytoprotective macroautophagy. Knockdown of ATF4 significantly reduced the levels of asparagine synthetase (ASNS) and overexpression of ASNS or supplementation of asparagine in trans, reversed the proliferation block and increased survival in ATF4 knockdown cells. Both amino acid and glucose deprivation, stresses found in solid tumours, activated the upstream eukaryotic initiation factor 2alpha (eIF2alpha) kinase GCN2 to upregulate ATF4 target genes involved in amino acid synthesis and transport. GCN2 activation/overexpression and increased phospho-eIF2alpha were observed in human and mouse tumours compared with normal tissues and abrogation of ATF4 or GCN2 expression significantly inhibited tumour growth in vivo. We conclude that the GCN2-eIF2alpha-ATF4 pathway is critical for maintaining metabolic homeostasis in tumour cells, making it a novel and attractive target for anti-tumour approaches.