Neuronal STING activation in amyotrophic lateral sclerosis and frontotemporal dementia

The stimulator of interferon genes (STING) pathway has been implicated in neurodegenerative diseases, including Parkinson's disease and amyotrophic lateral sclerosis (ALS). While prior studies have focused on STING within immune cells, little is known about STING within neurons. Here, we document neuronal activation of the STING pathway in human postmortem cortical and spinal motor neurons from individuals affected by familial or sporadic ALS. This process takes place selectively in the most vulnerable cortical and spinal motor neurons but not in neurons that are less affected by the disease. Concordant STING activation in layer V cortical motor neurons occurs in a mouse model of C9orf72 repeat-associated ALS and frontotemporal dementia (FTD). To establish that STING activation occurs in a neuron-autonomous manner, we demonstrate the integrity of the STING signaling pathway, including both upstream activators and downstream innate immune response effectors, in dissociated mouse cortical neurons and neurons derived from control human induced pluripotent stem cells (iPSCs). Human iPSC-derived neurons harboring different familial ALS-causing mutations exhibit increased STING signaling with DNA damage as a main driver. The elevated downstream inflammatory markers present in ALS iPSC-derived neurons can be suppressed with a STING inhibitor. Our results reveal an immunophenotype that consists of innate immune signaling driven by the STING pathway and occurs specifically within vulnerable neurons in ALS/FTD.

Neuroprotection of quercetin on central neurons against chronic high glucose through enhancement of Nrf2/ARE/glyoxalase-1 pathway mediated by phosphorylation regulation

Although dietary flavonoid quercetin alleviates diabetes-associated cognitive decline in rodents, the mechanisms are not clearly clarified. This study was designed to investigate whether quercetin showed neuroprotection on central neurons against chronic high glucose through the enhancement of Nrf2/ARE/glyoxalase 1 (Glo-1) pathway. SH-SY5Y cells were divided into 8 groups: normal glucose, high glucose (HG), osmotic pressure control, solvent control, HG plus low, middle, high concentrations of quercetin, or Nrf2 activator (sulforaphane). After treatment for 72 h, the associated parameters were measured. We found quercetin and sulforaphane increased cell viability, and enhanced Glo-1 functions (Glo-1 activity, the reduced glutathione and advanced glycation end-products levels) as well as Glo-1 protein and mRNA levels in SH-SY5Y cells cultured with HG. Meanwhile, quercetin and sulforaphane activated Nrf2/ARE pathway, reflected by the raised Nrf2 and p-Nrf2 levels, and the elevated protein and mRNA levels of γ-glutamycysteine synthase (γ-GCS), a known target gene of Nrf2/ARE signaling. Moreover, Nrf2/ARE pathway was activated after pretreatment with a PKC activator, p38 MAPK inhibitor, or GSK-3β inhibitor under the condition of HG, and quercetin addition further strengthened this pathway; however, PKC inhibition or GSK-3β activation pretreatment reversed the effects of quercetin on the protein expression of γ-GCS in the HG condition. In summary, quercetin exerts the neuroprotection by enhancing Glo-1 functions in central neurons under chronic HG condition, which may be mediated by activation of Nrf2/ARE pathway; furthermore, the increased Nrf2 phosphorylation mediated by PKC activation and/or GSK-3β inhibition may involve in the activation of Nrf2/ARE pathway.