The Neuroprotective Mechanisms of PPAR‐γ: Inhibition of Microglia‐Mediated Neuroinflammation and Oxidative Stress in a Neonatal Mouse Model of Hypoxic‐Ischemic White Matter Injury

ABSTRACT Background Neuroinflammation and oxidative stress, mediated by microglial activation, hinder the development of oligodendrocytes (OLs) and delay myelination in preterm infants, leading to white matter injury (WMI) and long‐term neurodevelopmental sequelae. Peroxisome proliferator‐activated receptor gamma (PPAR‐γ) has been reported to inhibit inflammation and oxidative stress via modulating microglial polarization in various central nervous system diseases. However, the relationship between PPAR‐γ and microglial polarization in neonatal WMI is not well understood. Therefore, this study aimed to elucidate the role and mechanisms of PPAR‐γ in preterm infants affected by WMI. Methods In this study, an in vivo hypoxia‐ischemia (HI) induced brain WMI neonatal mouse model was established. The mice were administered intraperitoneally with either RSGI or GW9662 to activate or inhibit PPAR‐γ, respectively. Additionally, an in vitro oxygen–glucose deprivation (OGD) cell model was established and pretreated with pcDNA 3.1‐PPAR‐γ or si‐PPAR‐γ to overexpress or silence PPAR‐γ, respectively. The neuroprotective effects of PPAR‐γ were investigated in vivo. Firstly, open field test, novel object recognization test, and beam‐walking test were employed to assess the effects of PPAR‐γ on neurobehavioral recovery. Furthermore, assessment of OLs loss and OL‐maturation disorder, the number of myelinated axons, myelin thickness, synaptic deficit, activation of microglia and astrocyte, and blood–brain barrier (BBB) were used to evaluate the effects of PPAR‐γ on pathological repair. The mechanisms of PPAR‐γ were explored both in vivo and in vitro. Assessment of microglia polarization, inflammatory mediators, reactive oxygen species (ROS), MDA, and antioxidant enzymes was used to evaluate the anti‐inflammatory and antioxidative effects of PPAR‐γ activation. An assessment of HMGB1/NF‐κB and NRF2/KEAP1 signaling pathway was conducted to clarify the mechanisms by which PPAR‐γ influences HI‐induced WMI in neonatal mice. Results Activation of PPAR‐γ using RSGI significantly mitigated BBB disruption, promoted M2 polarization of microglia, inhibited activation of microglia and astrocytes, promoted OLs development, and enhanced myelination in HI‐induced WMI. Conversely, inhibition of PPAR‐γ using GW9662 further exacerbated the pathologic hallmark of WMI. Neurobehavioral tests revealed that neurological deficits were ameliorated by RSGI, while further aggravated by GW91662. In addition, activation of PPAR‐γ significantly alleviated neuroinflammation and oxidative stress by suppressing HMGB1/NF‐κB signaling pathway and activating NRF2 signaling pathway both in vivo and in vitro. Conversely, inhibition of PPAR‐γ further exacerbated HI or OGD‐induced neuroinflammation, oxidative stress via modulation of the same signaling pathway. Conclusions Our findings suggest that PPAR‐γ regulates microglial activation/polarization as well as subsequent neuroinflammation/oxidative stress via the HMGB1/NF‐κB and NRF2/KEAP1 signaling pathway, thereby contributing to neuroprotection and amelioration of HI‐induced WMI in neonatal mice.