Effects of age, experience and inter-alpha inhibitor proteins on working memory and neuronal plasticity after neonatal hypoxia-ischemia

Abstract

Neonatal cerebral hypoxia-ischemia (HI) commonly results in cognitive and sensory impairments. Early behavioral experience has been suggested to improve cognitive and sensory outcomes in children and animal models with perinatal neuropathology. In parallel, we previously showed that treatment with immunomodulator Inter-alpha Inhibitor Proteins (IAIPs) improves cellular and behavioral outcomes in neonatal HI injured rats. The purpose of the current study was to evaluate the influences of early experience and typical maturation in combination with IAIPs treatment on spatial working and reference memory after neonatal HI injury. A second aim was to determine the effects of these variables on hippocampal CA1 neuronal morphology. Subjects were divided into two groups that differed with respect to the time when exposed to eight arm radial water maze testing: Group one was tested as juveniles (early experience, Postnatal day (P) 36 to 61) and adults (P88 – 113), and Group two was tested in adulthood only (P88-113; without early experience). Three treatment conditions were included in each experience group (HI + Vehicle, HI + IAIPs, and Sham subjects). Incorrect arm entries (errors) were compared between treatment and experience groups across three error types (Reference memory (RM), Working memory incorrect (WMI), Working memory correct (WMC)). Early experience led to improved working memory performance regardless of treatment. Combining IAIPs intervention with early experience provided a long-term behavioral advantage on the WMI component of the task in HI animals. Anatomically, early experience led to a decrease in the average number of basal dendrites per CA1 pyramidal neuron for IAIP treated subjects and a significant reduction in basal dendritic length in control subjects, highlighting the importance of pruning in typical early life learning. Our results support the hypothesis that early behavioral experience combined with IAIPs improve outcome on a relativity demanding cognitive task, beyond that of a single intervention strategy, and appears to facilitate neuronal plasticity following neonatal brain injury.

Expression and localization of Inter-alpha Inhibitors in rodent brain

“…Thus, taken together with our in vitro findings, IAIPs expression in different brain regions and cell types in vivo suggest the potential for diverse functions in healthy brain and potentially in neonatal related brain disorders. Moreover, our recent finding that exogenous blood derived IAIPs have important neuroprotective effects (Threlkeld et al, 2014, Gaudet et al, 2016) would appear to suggest that endogenous IAIPs could also exert neuroprotective effects analogous to other previously reported neuroprotective factors such as FGF-2 (Nozaki et al, 1993, Noda et al, 2014). …”

“…Exogenous IAIPs exhibit anti-inflammatory and neuroprotective effects in neonatal hypoxic-ischemic brain injury (Singh et al, 2010, Threlkeld et al, 2014, Gaudet et al, 2016). We have identified the wide spread existence of endogenous IAIPs in brain and other organs (Spasova et al, 2014), which has suggested the importance of examining the cellular expression and localization of IAIPs in brain as a first step to understand the physiological and molecular mechanisms of IAIPs in brain.…”

“…Impairment of this balance could lead to neurological injury such as hypoxia-ischemia-induced brain damage and neurodegenerative diseases (Sutton et al, 1994, Wang et al, 1998, Vivien and Buisson, 2000). As a canonical protein inhibitor of serine proteases, exogenous IAIPs are gaining increasing attention based upon their potential therapeutic benefits in sepsis and neonatal hypoxic-ischemic brain injury (Singh et al, 2010, Threlkeld et al, 2014, Gaudet et al, 2016). …”

“…Very little information is available regarding IAIPs in CNS. We recently have identified endogenous IaI and PaI proteins in cerebral cortex, choroid plexus and cerebral spinal fluid of sheep during development and have shown that exogenous treatment with IAIPs reduce neuronal cell death and improve behavioral outcomes in neonatal rats exposed to hypoxic-ischemic brain injury (Spasova et al, 2014, Threlkeld et al, 2014, Gaudet et al, 2016). Others have shown beneficial effects of the light chain, bikunin, in cerebral ischemia-reperfusion injury and experimental autoimmune encephalomyelitis (Yano et al, 2003, Koga et al, 2010, Shu et al, 2011).…”

“…Although we identified both the IaI and PaI proteins in the cerebral cortex of sheep (Spasova et al, 2014), more detailed information regarding the expression and localization of IAIPs in different cell types in the fetal and neonatal brain is lacking. Expression of endogenous IAIPs in cortical and hippocampal neurons may be of great importance given our previous observation that exogenous treatment with IAIPs attenuated cortical neuronal loss, improved behavioral outcomes, and decreased the number of basal dendrites per CA1 pyramidal neuron in the hippocampus of neonatal rats exposed to hypoxic ischemic brain injury (Threlkeld et al, 2014, Gaudet et al, 2016). Therefore, we reasoned that it would also be important to determine whether endogenous IAIPs were expressed by neurons in these critical brain regions.…”