Intranasal IL-4 Administration Alleviates Functional Deficits of Periventricular Leukomalacia in Neonatal Mice

Abstract

Background: Periventricular leukomalacia (PVL) is the major form of brain injury in premature infants. Currently, there are no therapies to treat PVL. Several studies suggested that polarization of microglia, a resident macrophage-like immune cell in the central nervous system, plays a vital role in brain injury and recovery. As an important mediator of immunity, interleukin-4 (IL-4) has critical effects on many immune cells, such as astrocytes and microglia. Increasing evidence shows that IL-4 plays a well-established role in attenuating inflammation in neurological disorders. Additionally, as a noninvasive and highly effective method, intranasal drug administration is gaining increasing attention. Therefore, in our study, we hypothesized that intranasal IL-4 administration is a promising strategy for PVL treatment. Methods: The therapeutic effects of IL-4 on neuroprotection were evaluated using a Control group, Hypoxia group, and Hypoxia + IL-4 treatment group. The PVL mouse model was established by a severe acute hypoxia (SAH) protocol. Exogenous IL-4 was intranasally administered to investigate its neuroprotective effects. A functional study was used to investigate neurological deficits, immunohistochemical technology and Western blotting were used to detect protein levels, and electron microscopy was used to evaluate myelination. Results: The results suggested that hypoxia stimulated Iba1 + microglial activation, downregulated myelin-related gene ( NG2, MAG , and MBP ) expression, reduced MBP protein levels, and caused neurological deficits. However, the intranasal administration of exogenous IL-4 partially inhibited Iba1+ microglial activation, improved myelination, and alleviated neurological deficits. The mechanistic study showed that IL-4 improved myelination possibly through the IL-4Ra-mediated polarization of microglia from the M1 phenotype to the M2 phenotype. Conclusion: In summary, our findings demonstrated that the intranasal administration of exogenous IL-4 improves myelination and attenuates functional deficits in a hypoxia-induced PVL model. Intranasal IL-4 administration may be a promising strategy for PVL treatment, for which further mechanistic studies are urgent.

Multi-Hit White Matter Injury-Induced Cerebral Palsy Model Established by Perinatal Lipopolysaccharide Injection

“…Norden et al demonstrated that repeated LPS injections (at regular intervals) did not magnify the inflammatory reaction, but instead stimulated the neuroprotective effect of microglia, suggesting that the protective effect of microglia may be time-dependent ( 49 ). A brain injury could surely activate microglia, and the M2-to-M1 microglial transition only occurred in the acute phase, but after a certain time, M2 started to dominate ( 27 , 50 ). We speculate that in our WMI-induced cerebral palsy model, such a time demarcation also exists.…”

“…Both in animals and humans, it has been found that males are more likely to show increased expression of inflammatory indicators and corresponding neurobehavioral symptoms in inflammatory encephalopathy, while females show resilience to neuroinflammation and less severe phenotype ( 51 – 53 ). Lin-Chao Yu et al used male mice when studying the therapeutic effect of IL-4 on periventricular leukomalacia to avoid the bias of gender in the experiment ( 50 ). In a detailed study of mice microglia, researchers found that a small cluster of extremely specific microglia is enriched in females, which is different from males, and sex only had little effect on microglia diversity ( 16 ).…”

“…The first limitation is that we only chose one marker protein for each type of microglia. There are other markers such as iNOS/CD16/CD86 for M1-type microglia and CD163/CD106 for M2-type microglia ( 27 , 50 ). Perhaps different markers can be applied in a future study to improve experimental accuracy.…”