Hypoxic-ischaemic damage to the developing brain is a leading cause of child death, with high mortality and morbidity, including cerebral palsy, epilepsy, and cognitive disabilities. The developmental stage of the brain and the severity of the insult influence the selective regional vulnerability and the subsequent clinical manifestations. The increased susceptibility to hypoxia-ischaemia (HI) of periventricular white matter in preterm infants predisposes the immature brain to motor, cognitive, and sensory deficits, with cognitive impairment associated with earlier gestational age. In term infants HI causes selective damage to sensorimotor cortex, basal ganglia, thalamus, and brain stem. Even though the immature brain is more malleable to external stimuli compared to the adult one, a hypoxic-ischaemic event to the neonate interrupts the shaping of central motor pathways and can affect normal developmental plasticity through altering neurotransmission, changes in cellular signalling, neural connectivity and function, wrong targeted innervation, and interruption of developmental apoptosis. Models of neonatal HI demonstrate three morphologically different types of cell death, that is, apoptosis, necrosis, and autophagy, which crosstalk and can exist as a continuum in the same cell. In the present review we discuss the mechanisms of HI injury to the immature brain and the way they affect plasticity.

Neonatal hypoxic ischaemic (HI) injury frequently causes neural impairment in surviving infants. Our knowledge of the underlying molecular mechanisms is still limited. Protein deimination is a post-translational modification caused by Ca+2-regulated peptidylarginine deiminases (PADs), a group of five isozymes that display tissue-specific expression and different preference for target proteins. Protein deimination results in altered protein conformation and function of target proteins, and is associated with neurodegenerative diseases, gene regulation and autoimmunity. In this study, we used the neonatal HI and HI/infection [lipopolysaccharide (LPS) stimulation] murine models to investigate changes in protein deimination. Brains showed increases in deiminated proteins, cell death, activated microglia and neuronal loss in affected brain areas at 48 h after hypoxic ischaemic insult. Upon treatment with the pan-PAD inhibitor Cl-amidine, a significant reduction was seen in microglial activation, cell death and infarct size compared with control saline or LPS-treated animals. Deimination of histone 3, a target protein of the PAD4 isozyme, was increased in hippocampus and cortex specifically upon LPS stimulation and markedly reduced following Cl-amidine treatment. Here, we demonstrate a novel role for PAD enzymes in neural impairment in neonatal HI Encephalopathy, highlighting their role as promising new candidates for drug-directed intervention in neurotrauma.Hypoxic Ischaemic Insult (HI) results in activation of peptidylarginine deiminases (PADs) because of calcium dysregulation. Target proteins undergo irreversible changes of protein bound arginine to citrulline, resulting in protein misfolding. Infection in synergy with HI causes up-regulation of TNFα, nuclear translocation of PAD4 and change in gene regulation as a result of histone deimination. Pharmacological PAD inhibition significantly reduced HI brain damage.

Background and Purpose In infants with moderate to severe neonatal encephalopathy, whole body cooling to 33-34°C for 72 hours is standard care with a number needed to treat to prevent one adverse outcome of 6-7. The precise brain temperature providing optimal neuroprotection is unknown. Methods After a quantified global cerebral hypoxic-ischemic insult, 28 piglets aged <24h were randomized (each group n=7) to: (i) normothermia (38.5°C throughout), or whole-body cooling 2-26 h post-insult to (ii) 35°C, (iii) 33.5°C or (iv) 30°C. At 48h post-insult, delayed cell death (TUNEL and cleaved caspase 3) and microglial ramification (Iba-1) were evaluated. Results At 48h post-insult, substantial cerebral injury was found in the normothermia and 30°C-hypothermia groups. However, with 35°C and 33.5°C cooling, a clear reduction in delayed cell death and microglial activation was observed in most brain regions (P<0.05), with no differences between 35°C and 33.5°C cooling groups. A protective pattern was observed, with U-shaped temperature dependence in delayed cell death in periventricular white matter, caudate nucleus, putamen, hippocampus and thalamus. A microglial activation pattern was also seen, with inverted U-shaped temperature dependence in periventricular white matter, caudate nucleus, internal capsule and hippocampus (all P<0.05). Conclusions Cooling to 35°C (an absolute drop of 3.5°C as in therapeutic hypothermia protocols) or to 33.5 °C provided protection in most brain regions after a cerebral hypoxic-ischemic insult in the newborn piglet. While the relatively wide therapeutic range of a 3.5-5°C drop in temperature was reassuring, overcooling (an 8.5°C drop) was clearly detrimental in some brain regions.

Alzheimer's disease (AD) onset is associated with changes in hypothalamic-pituitary−gonadal (HPG) function. The 54 amino acid kisspeptin (KP) peptide regulates the HPG axis and alters antioxidant enzyme expression. The Alzheimer's amyloid-β (Aβ) is neurotoxic, and this action can be prevented by the antioxidant enzyme catalase. Here, we examined the effects of KP peptides on the neurotoxicity of Aβ, prion protein (PrP), and amylin (IAPP) peptides. The Aβ, PrP, and IAPP peptides stimulated the release of KP and KP 45−54. The KP peptides inhibited the neurotoxicity of Aβ, PrP, and IAPP peptides, via an action that could not be blocked by kisspeptin-receptor (GPR-54) or neuropeptide FF (NPFF) receptor antagonists. Knockdown of KiSS-1 gene, which encodes the KP peptides, in human neuronal SH-SY5Y cells with siRNA enhanced the toxicity of amyloid peptides, while KiSS-1 overexpression was neuroprotective. A comparison of the catalase and KP sequences identified a similarity between KP residues 42−51 and the region of catalase that binds Aβ. The KP peptides containing residues 45−50 bound Aβ, PrP, and IAPP, inhibited Congo red binding, and were neuroprotective. These results suggest that KP peptides are neuroprotective against Aβ, IAPP, and PrP peptides via a receptor independent action involving direct binding to the amyloid peptides. KEYWORDS: KiSS-1, kisspeptin, amyloid-β, prion protein, amylin, neuroprotection N euroendocrine hormone changes are seen in aging, and there are disease specific changes associated with Alzheimer's disease (AD). 1,2 One of the neuroendocrine systems to show profound changes with aging is the hypothalamic−pituitary−gonadal (HPG) system, and the pathology of AD, Creutzfeldt−Jakob disease (CJD), and type 2 diabetes mellitus (T2DM) is also associated with changes in the hormones of this system. 3,4 A major regulator of the HPGaxis is the 54 amino acid kisspeptin (KP) peptide, which acts on gonadotrophin-releasing hormone (GnRH) neurons to activate GnRH release. 5 The KP peptide is produced in neurons by processing of the KiSS-1 preproprotein to yield the 54 amino acid KP peptide, which corresponds to residues 68−121 of KiSS-1. 6 Shorter derivatives of KP peptide comprising the C-terminal 14 (KP 41−54), 13 (KP 42−54), and 10 (KP 45−54) amino acids have also been found in tissues and corresponding to residues 108− 121, 109−121, and 112−121 of KiSS-1. 6,7 Biological activity of KP peptides requires the KP 45−54 sequence and is mediated via a specific KP receptor (GPR-54). 6,7 Lack of KP signaling via the GPR-54 receptor is associated with reproductive system failure. 8 Cleavage of the KP 45−54 peptide between residues 51 and 52 by matrix metalloproteinases abolishes the activation of GPR-54 by the KP 45−54 peptide. 9 The KP 42−54 and KP 45−54 peptides also activate NPFF receptors, 10,11 and some of the actions of KP peptides could be mediated by NPFF receptor activation.There are profound changes in KP signaling at menopause 12 and notable sex differences in hypothalamic neurodegenera...