Stimulation of insulin signaling and inhibition of JNK-AP1 activation protect cells from amyloid-\u3b2-induced signaling dysregulation and inflammatory response

One of the hallmarks of Alzheimer's disease (AD) is the accumulation and deposition of amyloid-\u3b2 (A\u3b2) peptides in the brain and cerebral vasculature. A\u3b2 evokes neuroinflammation and has been implicated in insulin signaling disruption and JNK-AP1 activation, contributing to AD neuropathologies including oxidative injury and vascular insufficiencies. In this study we aim to better understand the protective mechanisms of insulin signaling and JNK-AP1 inhibition on the adverse effects of A\u3b2. Four-hour treatment of hCMEC/D3, the immortalized human brain endothelial cells (iHBEC), with A\u3b21-42 resulted in significant c-Jun phosphorylation, oxidative stress, and cell toxicity. Concurrent treatment with A\u3b21-42 and insulin or A\u3b21-42 and JNK inhibitor SP600125 significantly improved cell viability. Cytokine array on conditioned media showed that insulin and SP600125 strongly reduced all A\u3b2 1-42-induced cytokines. ELISA confirmed the protective effect of insulin and SP600125 on A\u3b2-induced expression of interleukin (IL)-8 and Growth related oncogene-\u3b1 (Gro-\u3b1). qRT-PCR revealed that insulin and SP600125 protected iHBEC from A\u3b21-42-induced inflammatory gene expression. Transcription factor profiling showed that treatment of iHBEC with A\u3b21-42, insulin, or SP600125 alone or in combination resulted in profound changes in modulating the activities of multiple transcription factors and relevant pathways, some of which were validated by western blot. Insulin treatment and JNK inhibition in vitro synergistically reduced c-Jun phosphorylation and thus JNK-AP1 signaling activation. The study suggests that activation of insulin and blocking of JNK-AP1 signaling inhibits A\u3b2-induced dysregulation of insulin signaling and inflammatory response.Peer reviewed: YesNRC publication: Ye

Nonsynonymous mutations within APOB in human familial hypobetalipoproteinemia: evidence for feedback inhibition of lipogenesis and postendoplasmic reticulum degradation of apolipoprotein B.

Five nontruncating missense APOB mutations, namely A31P, G275S, L324M, G912D, and G945S, were identified in heterozygous carriers of familial hypobetalipoproteinemia (FHBL) in the Italian population. To test that the FHBL phenotype was a result of impaired hepatic secretion of mutant apoB proteins, we performed transfection studies using McA-RH7777 cells stably expressing wild type or mutant forms of human apolipoprotein B-48 (apoB-48). All mutant proteins displayed varied impairment in secretion, with G912D the least affected and A31P barely secreted. Although some A31P was degraded by proteasomes, a significant proportion of it (although inappropriately glycosylated) escaped endoplasmic reticulum (ER) quality control and presented in the Golgi compartment. Degradation of the post-ER A31P was achieved by autophagy. Expression of A31P also decreased secretion of endogenous apoB and triglycerides, yet the impaired lipoprotein secretion did not lead to lipid accumulation in the cells or ER stress. Rather, expression of genes involved in lipogenesis was down-regulated, including liver X receptor alpha, sterol regulator element-binding protein 1c, fatty acid synthase, acetyl-CoA carboxylase 1, stearoyl-CoA desaturase 1, and lipin-1. These results suggest that feedback inhibition of hepatic lipogenesis in conjunction with post-ER degradation of misfolded apoB proteins can contribute to reduce fat accumulation in the FHBL liver