RESUMO
AGEs (advanced glycation-end products) accumulate during aging and several pathologies such as Alzheimer's disease and diabetes. These protein products are known to inhibit proteolytic pathways. Moreover, AGEs are known to be involved in the activation of immune responses. In the present study we demonstrate that AGEs induce the expression of immunoproteasomal subunits. To elucidate a molecular basis underlying the observed effects we were able to demonstrate an activation of the Jak2 (Janus kinase 2)/STAT1 (signal transducer and activator of transcription 1) pathway. Inhibition of Jak2 by AG-490 and STAT1 by specific siRNA (small interfering RNA) abolished AGE-induced expression of immunoproteasomal subunits. Furthermore, silencing of RAGE (receptor for AGEs) revealed that AGE-induced up-regulation of the immunoproteasome is mediated by a RAGE signalling process. Thus we have described for the first time that the signalling pathway of Jak2 and STAT1 activated by AGEs via RAGE is involved in the induction of the immunoproteasome.
Assuntos
Produtos Finais de Glicação Avançada/farmacologia , Janus Quinase 2/fisiologia , Complexo de Endopeptidases do Proteassoma/metabolismo , Receptores Imunológicos/fisiologia , Fator de Transcrição STAT1/fisiologia , Transdução de Sinais/fisiologia , Animais , Linhagem Celular Tumoral/metabolismo , Cisteína Endopeptidases/biossíntese , Cisteína Endopeptidases/genética , Regulação da Expressão Gênica/genética , Interferon gama/fisiologia , Macrófagos/metabolismo , Camundongos , Fosforilação/efeitos dos fármacos , Complexo de Endopeptidases do Proteassoma/biossíntese , Complexo de Endopeptidases do Proteassoma/genética , Processamento de Proteína Pós-Traducional/efeitos dos fármacos , RNA Mensageiro/biossíntese , RNA Interferente Pequeno/farmacologia , Receptor para Produtos Finais de Glicação Avançada , Receptores Imunológicos/biossíntese , Receptores Imunológicos/genética , Soroalbumina Bovina/farmacologia , Transcrição Gênica/efeitos dos fármacos , Tirfostinas/farmacologiaRESUMO
Advanced glycation end product-modified proteins are known for accumulating during aging and in several pathological conditions such as diabetes, renal failure, and neurodegenerative disorders. There is little information about the intracellular fate of endocytosed advanced glycation end products (AGEs) and their influence on proteolytic systems. However, it is known that the lysosomal system is impaired during aging. Therefore, undegraded material may accumulate and play a considerable role in the development of diverse diseases. To investigate if AGEs can be degraded and to test whether they accumulate because of impaired lysosomal proteases we studied the effects of advanced glycation end products on the endosomal-lysosomal system. Five different types of AGEs were generated by bovine serum albumin incubation with glyoxal, methylglyoxal, glucose, fructose, and ribose. The first experiments revealed the uptake of AGEs by the macrophage cell line RAW 264.7. Further investigations demonstrated an increase in cathepsin D and L activity and an increase in mature cathepsins D and L. Increased activities were accompanied by the presence of more lysosomes, measured by staining with LysoTracker blue. To specify the roles of cathepsins D and L we used knockout cells to test the roles of both cathepsins on the toxicity of advanced glycation end products. In summary we conclude that both cathepsins are required for a reduction in advanced glycation end product-induced cytotoxicity.
