Differentiated HT22 cells as a novel model for in vitro screening of serotonin reuptake inhibitors

Cytosolic Escape of Mitochondrial DNA Triggers cGAS-STING Pathway-Dependent Neuronal PANoptosis in Response to Intermittent Hypoxia

Intermittent hypoxia (IH) is the predominant pathophysiological disturbance in obstructive sleep apnea (OSA), characterized by neuronal cell death and neurocognitive impairment. We focus on the accumulated mitochondrial DNA (mtDNA) in the cytosol, which acts as a damage-associated molecular pattern (DAMP) and activates the cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) pathway, a known trigger for immune responses and neuronal death in degenerative diseases. However, the specific role and mechanism of the mtDNA-cGAS-STING axis in IH-induced neural damage remain largely unexplored. Here, we investigated the involvement of PANoptosis, a novel type of programmed cell death linked to cytosolic mtDNA accumulation and the cGAS-STING pathway activation, in neuronal cell death induced by IH. Our study found that PANoptosis occurred in primary cultures of hippocampal neurons and HT22 cell lines exposed to IH. In addition, we discovered that during IH, mtDNA released into the cytoplasm via the mitochondrial permeability transition pore (mPTP) activates the cGAS-STING pathway, exacerbating PANoptosis-associated neuronal death. Pharmacologically inhibiting mPTP opening or depleting mtDNA significantly reduced cGAS-STING pathway activation and PANoptosis in HT22 cells under IH. Moreover, our findings indicated that the cGAS-STING pathway primarily promotes PANoptosis by modulating endoplasmic reticulum (ER) stress. Inhibiting or silencing the cGAS-STING pathway substantially reduced ER stress-mediated neuronal death and PANoptosis, while lentivirus-mediated STING overexpression exacerbated these effects. In summary, our study elucidates that cytosolic escape of mtDNA triggers cGAS-STING pathway-dependent neuronal PANoptosis in response to IH, mainly through regulating ER stress. The discovery of the novel mechanism provides theoretical support for the prevention and treatment of neuronal damage and cognitive impairment in patients with OSA.

GSK4716 enhances 5-HT1AR expression by glucocorticoid receptor signaling in hippocampal HT22 cells

OBJECTIVES

The serotonin (5-hydroxytryptamine, 5-HT) receptor 1A (5-HT1AR) is closely associated with serotonergic neurotransmission in the brain, being the most prevalent and widely distributed receptor of its kind. The purpose of this study is to investigate the regulation mechanism of 5-HT1AR by GSK4716.

METHODS

To investigate the mechanism of GSK4716-mediated 5-HT1AR regulation, we used hippocampus-derived HT22 cells expressing 5-HT1AR. The expression level of 5-HT1AR and associated proteins, were detected by reporter gene assay and western blotting.

RESULTS

GSK4716, an estrogen-related receptor gamma agonist increased 5-HT1AR expression by interacting with the GR, a repressor of 5-HT1AR transcription. Dexamethasone, a GR agonist, decreased the GSK4716-induced increase in 5-HT1AR, which was associated with an alteration in nuclear GR. Furthermore, GR antagonist RU486 reversed the effects induced by dexamethasone, including the elevation of nuclear GR levels and the reduction of 5-HT1AR transcription and expression.

CONCLUSION

The results could provide insight into the potential applications of small molecules, such as GSK4716, in the regulation of 5-HT1AR expression, which plays a role in serotonergic neurotransmission.

Reducing polypyrimidine tract‑binding protein 1 fails to promote neuronal transdifferentiation on HT22 and mouse astrocyte cells under physiological conditions

In contrast to prior findings that have illustrated the conversion of non-neuronal cells into functional neurons through the specific targeting of polypyrimidine tract-binding protein 1 (PTBP1), accumulated evidence suggests the impracticality of inducing neuronal transdifferentiation through suppressing PTBP1 expression in pathological circumstances. Therefore, the present study explored the effect of knocking down PTBP1 under physiological conditions on the transdifferentiation of mouse hippocampal neuron HT22 cells and mouse astrocyte (MA) cells. A total of 20 µM negative control small interfering (si)RNA and siRNA targeting PTBP1 were transfected into HT22 and MA cells using Lipo8000™ for 3 and 5 days, respectively. The expression of early neuronal marker βIII-Tubulin and mature neuronal markers NeuN and microtubule-associated protein 2 (MAP2) were detected using western blotting. In addition, βIII-tubulin, NeuN and MAP2 were labeled with immunofluorescence staining to evaluate neuronal cell differentiation in response to PTBP1 downregulation. Under physiological conditions, no significant changes in the expression of βIII-Tubulin, NeuN and MAP2 were found after 3 and 5 days of knockdown of PTBP1 protein in both HT22 and MA cells. In addition, the immunofluorescence staining results showed no apparent transdifferentiation in maker levels and morphology. The results suggested that the knockdown of PTBP1 failed to induce neuronal differentiation under physiological conditions.