GSK-2606414

Enzymatically formed side-chain oxysterols function as signaling molecules regulating cholesterol homeostasis and act as intermediates in the biosynthesis of bile acids. In addition to these physiological functions, an imbalance in oxysterol homeostasis has been implicated in pathophysiology. Cholesterol 25-hydroxylase (CH25H) and its product 25-hydroxycholesterol (25-OHC), also formed by autoxidation, are associated with amyotrophic lateral sclerosis. However, the effects of 25-OHC on cell viability in glial cells remain unclear. This study demonstrates that 25-OHC induces ferroptosis, an iron-dependent programmed cell death, in mouse Schwann IMS32 cells. Mechanistically, 25-OHC suppressed the expression of selenoprotein glutathione peroxidase 4 (GPX4) at both the transcriptional and translational levels by inhibiting the processing of sterol regulatory element-binding proteins (SREBPs). In addition, 25-OHC upregulated the expression of NADH-cytochrome b5 reductase 1 (CYB5R1) and NADPH-cytochrome P450 reductase (POR), enzymes that promote lipid peroxidation. We further found that 25-OHC increases the expression of glutathione-specific gamma-glutamylcyclotransferase 1 (CHAC1) and decreases glutathione levels. Importantly, non-cytotoxic concentrations of 25-OHC enhanced cellular sensitivity to ferroptosis inducers by downregulating GPX4 expression. These findings reveal a multifaceted approach whereby 25-OHC induces ferroptosis through SREBP pathway suppression and redox imbalance in mouse Schwann IMS32 cells.

Ferroptosis is involved in neurodegenerative disorders including diabetes-associated cognitive impairment (DACI). As central immune cells, microglia have strong siderophilic properties. However, the role of iron deposition in microglia and the underlying regulatory mechanism remains unclear in DACI. Here, we established high glucose (HG) model in BV2/HMC3 cells and diabetes model in C57BL/6 J mice with HFD and STZ. Transmission Electron Microscopy, Western blot, assay kits of Fe²⁺, GSH/GSSG, MDA and ROS were carried out in vitro. Prussian blue staining, Western blot and immunofluorescence were implemented in vivo. Y-maze and novel object recognition were performed to assess cognitive performance. LP17 was used to inhibit TREM1 (triggering receptor expressed on myeloid cells 1) specifically in vivo and vitro. We found excessively deposited iron and significant reduction in antioxidants in hippocampal microglia of mice with DACI, concomitant with increased TREM1 (a microglia-specific inflammatory amplifier). Furthermore, LP17 (TREM1 specific inhibitor) ameliorated cognitive impairment caused by HFD/STZ through relieving iron accumulation and antioxidant inactivation. In vitro, ferroptosis was induced by HG in mice microglia-BV2 and human microglia-HMC3 cells, which could be blocked by a ferroptosis inhibitor-Fer-1 and LP17. Moreover, PERK pathway of endoplasmic reticulum stress was activated by HG, and then reversed by PERK inhibitor GSK2606414 and LP17 followed by improved ferroptosis in HG-cultured BV2. In summary, our results indicated that TREM1 effectively aggravates T2DM-associated microglial iron accumulation through the PERK pathway of ERS, which contributes to antioxidant inactivation and lipid peroxidation, eventually, massively boosted ROS result in microglial ferroptosis. The mechanism elucidation in our study may shed light on targeted therapy of DACI.