Introduction

Intracerebral hemorrhage (ICH) accounts for 10–30% of all stroke subtypes, but with mortality of 50% at 1 year [1, 2]. The most frequent occurrence location of ICH is basal ganglia and thalamus, which are rich in white matter fibers [3]. When ICH occurs, blood enters the brain parenchyma from the ruptured blood vessel, leading to primary and secondary brain injury, both of which impact the structure and function of white matter fibers [4, 5]. Studies have reported that white matter injury (WMI) often occurs after ICH, and is considered an important predictor of the outcome [6]. However, most of the previous treatments for ICH focus on neuronal protection but paid insufficient attention to the protection of WMI. Therefore, the repair of WMI is expected to become a new treatment strategy for ICH.

Oligodendrocyte progenitor cells (OPCs) present as a pool of migratory and proliferative progenitor cells in the adult central nervous system (CNS), which differentiate into mature oligodendrocytes and re-myelinate damaged axons in diseases such as multiple sclerosis and stroke [7]. However, OPCs and oligodendrocytes are both vulnerable to cytotoxic and excitotoxic factors, and in vivo, how to differentiate OPCs to mature oligodendrocytes and remyelinate damaged axons has always been a difficult problem to overcome [8, 9]. Therefore, inhibiting OPC cell death and maintaining the stability of the OPC pool is the prerequisite for myelin repair.

Ferroptosis is a newly identified type of cell death, driven by iron-dependent phospholipid peroxidation [10]. This unique cell death is regulated by multiple cellular metabolic events, including iron metabolism, redox homeostasis, amino acid metabolism, mitochondrial function, and numerous signaling pathways [11]. Glutathione peroxidase 4 (GPx4) is an antioxidant enzyme catalyzing the glutathione (GSH)-dependent reduction of membrane lipid hydroperoxides (L-OOH) to lipid alcohols (L-OH), which limits the lipid peroxide in the cell membrane. Cystine/glutamate antiporter system χc–/GSH/GPX4 axis is a classical pathway protecting against ferroptosis, in which GPx4 is considered to be the key regulator in cancer cells and neurons [12,13,14,15]. Although we and others have demonstrated that ferroptosis is an important cell death form in cancers and CNS diseases, such as stroke [10, 14,15,8]. Mature oligodendrocytes are derived from oligodendrocyte progenitor cells (OPCs), which originate from neuroepithelial progenitor cells of neuroepithelium in the embryonic neural tube and the periventricular germinal area (retain in adult animals and known as the subventricular zone, SVZ) during embryogenesis and early postnatal period [27]. The previous research has proved that OPCs originate in the SVZ and migrated into corpus callosum (CC), striatum, and fimbria fornix to differentiate into mature oligodendrocytes in adult mice [28], indicated that OPCs in the SVZ of the brain contribute to oligodendrogenesis throughout life and rescuing OPC cell death could be an efficient strategy to treat myelin defects-related CNS diseases.

In this study, we injected autologous blood into the lateral ventricle of mice to study the pathological process of hemorrhage on OPCs and to prevent the interference of neuronal ferroptosis in outcome elevations in vivo. After intraventricular stroke (IVH), blood enters the lateral ventricle, which first produces huge pressure and space-occupying effect on the structures around the ventricle, increases intracranial pressure, reduces blood flow and oxygen metabolism, and may destroy the permeability of the blood–brain barrier and blood-cerebrospinal fluid barrier [32]. Combined with recent research that hemoglobin causes damage to mitochondrial function in primary cultured OPCs and inhibits OPC proliferation [33], our work further emphasizes the importance of protecting OPC against cell death after hemorrhagic stroke to reduce WMI.

On the other hand, we observed a small number of other cells colocalized with PI, suggesting that cell death in OPCs is an important but not exclusive mechanism for WMI after IVH. Although a mechanistic contribution of OPC-specific cell death to WMI is reported here, it is conceivable that the crosstalk of OPCs and other cells, such as microglia/macrophages, astrocytes, and neurons, in the pathogenesis of WMI is also of significant importance and requires further studies.

Ferroptosis, a new form of iron‐dependent programmed cell death, has been shown to be involved in a range of CNS diseases, such as stroke, traumatic brain injury, neural degeneration, and autoimmune demyelination in the context of multiple sclerosis and its mouse model of EAE [14, 34,35,Hindlimb placing test

We tested each mouse for Hindlimb placing test on days 1, 3, 7, 14, and 28 post IVH as described previously [14]. The mice were placed on the edge of the table, and the contralateral hind limbs were gently pulled below the edge of the table to observe the retraction of the animal limbs. Quickly retract and place on the edge of the table accurately, scored 0 point; delayed pullback, scored 1 point; no retraction of the limbs, scored 2 points. A total of 10 successful experiments were performed and the total score was recorded for each mouse.

Gait analysis

Gait analysis was performed using the Catwalk gait analysis system (Noldus Information Technology, The Netherlands) as described previously [54, 55]. In brief, the mice were placed in the dark experimental environment for 0.5 h for adaption before each experiment. At the beginning of the trial, the mouse was placed individually on the walkway and walked freely traverse from one side to another of the walkway glass plate where has a goal box. The videos of footprint images were recorded by a camera positioned under the walkway. The records were converted into digital signatures and processed using CatWalk XT 10.6 software. All mice completed three times of runs with an interval of 10 min. Mice were trained for 3 days prior to the record of baseline (the day before surgery), and the gait was assessed at −1 (baseline), 14, and 28 days after IVH/sham surgery.

Statistical analysis

Data are presented as mean ± SD, all statistical analyses were carried out with GraphPad Prism 7.0 Software. P values were calculated with a two-tailed Student’s unpaired t test for two groups. One-way analysis of variance (ANOVA) was used for comparisons within multiple groups. Two-way ANOVA was used to evaluate groups differentially regulated by the time factor. Tukey’s post hoc test or Dunnett’s post hoc test was used to determine specific differences between groups. P values of <0.05 indicated statistically significant differences.