Stimulation of Insulin Signaling and Inhibition of JNK-AP1 Activation Protect Cells from Amyloid-β-Induced Signaling Dysregulation and Inflammatory Response

Abstract

One of the hallmarks of Alzheimer's disease (AD) is the accumulation and deposition of amyloid-β (Aβ) peptides in the brain and cerebral vasculature. Aβ 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 Aβ. Four-hour treatment of hCMEC/D3, the immortalized human brain endothelial cells (iHBEC), with Aβ1-42 resulted in significant c-Jun phosphorylation, oxidative stress, and cell toxicity. Concurrent treatment with Aβ1-42 and insulin or Aβ1-42 and JNK inhibitor SP600125 significantly improved cell viability. Cytokine array on conditioned media showed that insulin and SP600125 strongly reduced all Aβ1-42-induced cytokines. ELISA confirmed the protective effect of insulin and SP600125 on Aβ-induced expression of interleukin (IL)-8 and Growth related oncogene-α (Gro-α). qRT-PCR revealed that insulin and SP600125 protected iHBEC from Aβ1-42-induced inflammatory gene expression. Transcription factor profiling showed that treatment of iHBEC with Aβ1-42, 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 Aβ-induced dysregulation of insulin signaling and inflammatory response.

Age and Its Association with Low Insulin and High Amyloid-β Peptides in Blood

“…Our data plus others [25, 26] suggest that high Aβ 40 is probably an aging factor that damages cerebrovasculature [27]. On the other hand, Aβ 42 , which is the major Aβ peptide depositing and more neurotoxic in the AD brain, impairs insulin signaling [28] and further induces Aβ 42 accumulation in the AD brain [29]. The majority of AD patients are sporadic, having a late onset (age =65) related to the aging process and often do not have significant genetic determinants for the disease.…”

Inhibition of c‐Jun N‐terminal kinase activation reverses Alzheimer disease phenotypes in APPswe/PS1dE9 mice

“…17,18 Several studies indicate that activated JNK plays a key role in tau hyperphosphorylation in vitro and in vivo. 23,24 In view of the above-stated evidence, these findings clearly indicate that activated JNK potentially contributes to the development of amyloid plaques, Ab production, tau hyperphosphorylation, neuroinflammation, and synaptic dysfunction associated with AD, suggesting that JNK activation represents a potential therapeutic target for the fight against AD. 23,24 In view of the above-stated evidence, these findings clearly indicate that activated JNK potentially contributes to the development of amyloid plaques, Ab production, tau hyperphosphorylation, neuroinflammation, and synaptic dysfunction associated with AD, suggesting that JNK activation represents a potential therapeutic target for the fight against AD.…”

“…Given the central role of fibrillar and oligomeric Ab in the activation of astrocytes and microglia cells with the consequent production of proinflammatory cytokines, 45 the decrease of neuroinflammatory responses may be secondary to the marked decrease of Ab pathologies seen in the SP600125-treated APPswe/PS1dE9 mice. 23,24 Thus, the beneficial effect of SP600125 treatment on decreased inflammatory responses in APPswe/ PS1dE9 mice can be mainly attributed to its direct antiinflammatory function via inhibiting JNK activation. 23,24 Thus, the beneficial effect of SP600125 treatment on decreased inflammatory responses in APPswe/ PS1dE9 mice can be mainly attributed to its direct antiinflammatory function via inhibiting JNK activation.…”

Aβ-Induced Insulin Resistance and the Effects of Insulin on the Cholesterol Synthesis Pathway and Aβ Secretion in Neural Cells

“…Several mechanisms may be involved in the development of the insulin-resistant phenotype in these cells. Ab peptides can cause c-Jun phosphorylation in SH-SY5Y cells as well as in human brain endothelial cells as we described previously [34,36], indicating the activation of c-Jun N-terminal kinase (JNK). Activated JNK may associate with IRS-1 and inhibit the insulin-stimulated tyrosine phosphorylation of IRS-1 and thus block the downstream transmission of insulin signaling [37,38].…”