Abbreviated Exposure to Hypoxia Is Sufficient to Induce CNS Dysmyelination, Modulate Spinal Motor Neuron Composition, and Impair Motor Development in Neonatal Mice

Abstract

Neonatal white matter injury (nWMI) is an increasingly common cause of cerebral palsy that results predominantly from hypoxic injury to progenitor cells including those of the oligodendrocyte lineage. Existing mouse models of nWMI utilize prolonged periods of hypoxia during the neonatal period, require complex cross-fostering and exhibit poor growth and high mortality rates. Abnormal CNS myelin composition serves as the major explanation for persistent neuro-motor deficits. Here we developed a simplified model of nWMI with low mortality rates and improved growth without cross-fostering. Neonatal mice are exposed to low oxygen from postnatal day (P) 3 to P7, which roughly corresponds to the period of human brain development between gestational weeks 32 and 36. CNS hypomyelination is detectable for 2–3 weeks post injury and strongly correlates with levels of body and brain weight loss. Immediately following hypoxia treatment, cell death was evident in multiple brain regions, most notably in superficial and deep cortical layers as well as the subventricular zone progenitor compartment. PDGFαR, Nkx2.2, and Olig2 positive oligodendrocyte progenitor cell were significantly reduced until postnatal day 27. In addition to CNS dysmyelination we identified a novel pathological marker for adult hypoxic animals that strongly correlates with life-long neuro-motor deficits. Mice reared under hypoxia reveal an abnormal spinal neuron composition with increased small and medium diameter axons and decreased large diameter axons in thoracic lateral and anterior funiculi. Differences were particularly pronounced in white matter motor tracts left and right of the anterior median fissure. Our findings suggest that 4 days of exposure to hypoxia are sufficient to induce experimental nWMI in CD1 mice, thus providing a model to test new therapeutics. Pathological hallmarks of this model include early cell death, decreased OPCs and hypomyelination in early postnatal life, followed by dysmyelination, abnormal spinal neuron composition, and neuro-motor deficits in adulthood.

Vascular Defects and Spinal Cord Hypoxia in Spinal Muscular Atrophy

“…16 A very recent report has shown that postnatal hypoxia significantly stunts growth and negatively modulates motor function. 35 Taken together, these studies point toward possible disease mechanisms.…”

Can Neonatal Systemic Inflammation and Hypoxia Yield a Cerebral Palsy-Like Phenotype in Periadolescent Mice?

“…The aetiology of the brain injuries leading to CP varies and is multi-factorial, and it includes hypoxia-ischaemia (HI), infection and inflammation, and affects different brain areas depending on the age of the foetus/infant [14, 15]. Several animal models of CP have been suggested, including the well-known hypoxic-ischaemic Rice-Vannucci model [16–18]; various inflammation models (mimicking early infection), which mostly use the lipopolysaccharide (LPS; one of the major components of Gram-negative bacterial cell wall), or the interleukin 1b (IL1b) cytokine as inflammatory agents [19–23]; models that use hypoxia alone [24]; a combination of inflammation and HI [25–28]; and a combination of inflammation and hypoxia [29, 30]. In the majority of the studies, inflammation was induced prenatally, either alone [22] or in combination with HI postnatally [26, 31].…”

Region specific oligodendrocyte transcription factor expression in a model of neonatal hypoxic injury

“…Using expression of transcription factors allows for an unambiguous identification of stages of oligodendrocyte development. Moreover, by using a milder form of hypoxia, such as in our model averts the presence of other cellular and molecular confounders seen in more severe injuries, such as necrosis and inflammation, that are normally present following hypoxia-ischemia (Rice et al, 1981;Vannucci, 1990) and more severe forms of global hypoxic injury, or a combination of the two (Back et al, 2002;Brazel et al, 2004;Segovia et al, 2008;van der Kooij et al, 2009;Watzlawik et al, 2015).…”