Loss of interneurons and disruption of perineuronal nets in the cerebral cortex following hypoxia-ischaemia in near-term fetal sheep

Abstract

Hypoxia-ischaemia (HI) in term infants is a common cause of brain injury and neurodevelopmental impairment. Development of gamma-aminobutyric acid (GABA)ergic circuitry in the cerebral cortex is a critical event in perinatal brain development. Perineuronal nets (PNNs) are specialised extracellular matrix structures that surround GABAergic interneurons, and are important for their function. Herein, we hypothesised that HI would reduce survival of cortical interneurons and disrupt PNNs in a near-term fetal sheep model of global cerebral ischaemia. Fetal sheep (0.85 gestation) received sham occlusion (n = 5) or 30 min of reversible cerebral ischaemia (HI group; n = 5), and were recovered for 7 days. Expression of interneurons (glutamate decarboxylase [GAD]+; parvalbumin [PV]+) and PNNs (Wisteria floribunda agglutinin, WFA) was assessed in the parasagittal cortex by immunohistochemistry. HI was associated with marked loss of both GAD+ and PV+ cortical interneurons (all layers of the parasagittal cortex and layer 6) and PNNs (layer 6). The expression and integrity of PNNs was also reduced on surviving GAD+ interneurons. There was a trend towards a linear correlation of the proportion of GAD+ neurons that were WFA+ with seizure burden (r2 = 0.76, p = 0.0534). Overall, these data indicate that HI may cause deficits in the cortical GABAergic system involving loss of interneurons and disruption of PNNs, which may contribute to the range of adverse neurological outcomes following perinatal brain injury.

Connexin Hemichannel Mimetic Peptide Attenuates Cortical Interneuron Loss and Perineuronal Net Disruption Following Cerebral Ischemia in Near-Term Fetal Sheep

“…In the present study, cerebral ischemia in near-term fetal sheep was associated with a pattern of parasagittal cortical damage after 7 days of recovery, which included a marked reduction in the survival of cortical GAD + , parvalbumin + , calretinin + , and calbindin + interneuron populations. These findings are broadly consistent with previous studies showing loss and disrupted development of interneurons in the cerebral cortex and subcortical grey matter following HI in preterm and term fetal sheep [17,[32][33][34][35] and neonatal rodents [36][37][38][39][40][41][42][43] and following ventilatory support in preterm baboons [44]. Although there are no comparable term human data, limited pathology and imaging studies in preterm infants have shown reductions in the numbers and complexity of cortical interneurons, refs [25,45] cortical interneuron migration, [7] interneuron neurogenesis, [46] and cortical GABAergic signaling [4].…”

“…There is increasing evidence that injury to cortical interneurons, including loss of PNNs and disruption of inhibitory interneuron circuits, is an important contributor to neurological disability following neonatal brain injury [17,25,26]. The present study demonstrates that blockade of connexin43 hemichannel opening with a mimetic peptide during early recovery from HI in term-equivalent fetal sheep improved survival of cortical GABAergic interneurons and prevented loss of cortical PNNs after 7 days of recovery.…”

“…Disruption of PNNs has also been reported in a range of neurological diseases such as schizophrenia, ref [14] Alzheimer's disease, ref [15] and epilepsy [16]. Further, we recently reported loss of PNNs on cortical interneurons after hypoxia-ischemia (HI) in term-equivalent fetal sheep [17]. Thus, changes in cortical interneuron PNN expression may be an important component of interneuron dysfunction and neurological disability following neonatal brain injury.…”

Hyperactive MEK1 signaling in cortical GABAergic neurons causes embryonic parvalbumin-neuron death and defects in behavioral inhibition

“…It will be important to evaluate whether treatment with pharmacological MEK1/2 inhibitors or antioxidants during embryogenesis is capable of sustained restoration of CIN number in caMek1 , Slc32A1:Cre mice. PV-CIN sensitivity to MEK1 hyperactivation may not only be an important factor in RASopathy neuropathology, but could be a relevant mechanism in other conditions that involve indirect activation of ERK/MAPK signaling during embryogenesis, such as schizophrenia, Fragile X Syndrome, or prenatal stress (Fowke et al, 2018).…”

Midkine: The Who, What, Where, and When of a Promising Neurotrophic Therapy for Perinatal Brain Injury

“…For example, in preterm born infants, there is a widespread interneuronopathy as these cells are still migrating throughout the last trimester, a period of development disturbed by their early birth (91,92). Interneuron damage in neonatal stroke and HIE is limited to the region of frank cell loss (93,94). A role for HIE in preterm born infants is not conclusively supported (95), but oxygen variability is a likely contributor to injury (96).…”