Combined fetal inflammation and postnatal hypoxia causes myelin deficits and autism‐like behavior in a rat model of diffuse white matter injury

Abstract

Diffuse white matter injury (WMI) is a serious problem in extremely preterm infants, and is associated with adverse neurodevelopmental outcome, including cognitive impairments and an increased risk of autism‐spectrum disorders. Important risk factors include fetal or perinatal inflammatory insults and fluctuating cerebral oxygenation. However, the exact mechanisms underlying diffuse WMI are not fully understood and no treatment options are currently available. The use of clinically relevant animal models is crucial to advance knowledge on the pathophysiology of diffuse WMI, allowing the definition of novel therapeutic targets. In the present study, we developed a multiple‐hit animal model of diffuse WMI by combining fetal inflammation and postnatal hypoxia in rats. We characterized the effects on white matter development and functional outcome by immunohistochemistry, MRI and behavioral paradigms. Combined fetal inflammation and postnatal hypoxia resulted in delayed cortical myelination, microglia activation and astrogliosis at P18, together with long‐term changes in oligodendrocyte maturation as observed in 10 week old animals. Furthermore, rats with WMI showed impaired motor performance, increased anxiety and signs of autism‐like behavior, i.e. reduced social play behavior and increased repetitive grooming. In conclusion, the combination of fetal inflammation and postnatal hypoxia in rats induces a pattern of brain injury and functional impairments that closely resembles the clinical situation of diffuse WMI. This animal model provides the opportunity to elucidate pathophysiological mechanisms underlying WMI, and can be used to develop novel treatment options for diffuse WMI in preterm infants.

Hypoxia and myelination deficits in the developing brain

“…First stage of oligodendrocytes development starts with differentiation of neural stem cells into OPCs and their migration to the designated destination. In the next stage, OPCs proliferate and differentiate into multipolar, mitotically active pre‐myelinating oligodendrocytes (van Tilborg et al, 2018; Back and Rosenberg, 2014). Later on, these pre‐myelinating oligodendrocytes gradually transform into mature myelinating oligodendrocytes and once their processes contact axons they start to produce large amounts of myelin and myelin associated proteins (Emery, 2010).…”

“…Later on, these pre‐myelinating oligodendrocytes gradually transform into mature myelinating oligodendrocytes and once their processes contact axons they start to produce large amounts of myelin and myelin associated proteins (Emery, 2010). Details of the OPCs development and maturation have been provided by many elegant studies (Kessaris et al, 2006; van Tilborg et al, 2018). In human fetal brain, first appearance of OPCs occurs at 10 weeks gestational age and expansion of OPCs population takes place between 15–20 weeks of gestational age.…”

“…In addition to oligodendrocytes, degenerating axons with distorted myelin sheaths represent a common feature in the developing brain in hypoxic insults (Kaur et al, 2006a). Delayed maturation of oligodendrocytes has been reported to underlie hypoxia induced impairment of myelination in the developing brain (van Tilborg et al, 2018). Several brain regions including the hippocampus, cerebral cortex and the striatum in postnatal rats following a hypoxic insult showed impeded maturation of the oligodendrocytes (Ziemka‐Nalecz et al, 2017).…”

“…Delayed oligodendrocyte differentiation (Jablonska et al, 2012; Iida et al, 1995; Paneth et al, 1990; Wellmann et al, 2015) and arrest of oligodendrocyte maturation also occurs in response to a hypoxic insult (Ness et al, 2001; Back et al, 2002) resulting in impaired or delayed myelination (Kurumatani et al, 1998; Jelinski et al, 1999; Cai et al, 2001). Impaired myelination is considered as a significant factor in the pathogenesis of neurological disabilities including cerebral palsy (Drobyshevsky et al, 2014), autism spectrum disorders (Lazar et al, 2014; van Tilborg et al, 2018), epilepsy (Scholl et al, 2017) and mental retardation (Takakura et al, 2015). In addition to cell death, swollen and degenerating axons, activated microglia and astrocytosis have been reported to occur in hypoxic injuries of the developing brain (Takashima et al, 1995; Skoff et al, 2001; Ness et al, 2001; Kaur et al, 2006a).…”

NG2 Glia: Novel Roles beyond Re-/Myelination

“…Recently, Minocha et al [63] developed two Cre-mouse lines expressing a 'floxed' diphtheria toxin gene under either the Nkx2.1 (Nkx2.1-Cre -R26DTA) or the NG2 (Cspg4-Cre-R26DTA) promoter to ablate the first wave of NG2 glia produced in the forebrain during the embryonic life. In the mouse, these cells originate at E12.5 from Nkx2.1-expressing progenitors of the medial ganglionic eminence and anterior entopeduncular area, and transiently populate the entire telencephalon by E14.5 before disappearing at around postnatal day eight (P8) [84,89,90]. Thus, they do not contribute to myelination and their transient nature raises numerous questions about their possible role/s during CNS development.…”