Enhanced autophagy contributes to excitotoxic lesions in a rat model of preterm brain injury

Oligodendrocyte progenitor cells' fate after neonatal asphyxia-Puzzling implications for the development of hypoxic-ischemic encephalopathy

Premature birth or complications during labor can cause temporary disruption of cerebral blood flow, often followed by long-term disturbances in brain development called hypoxic-ischemic (HI) encephalopathy. Diffuse damage to the white matter is the most frequently detected pathology in this condition. We hypothesized that oligodendrocyte progenitor cell (OPC) differentiation disturbed by mild neonatal asphyxia may affect the viability, maturation, and physiological functioning of oligodendrocytes. To address this issue, we studied the effect of temporal HI in the in vivo model in P7 rats with magnetic resonance imaging (MRI), microscopy techniques and biochemical analyses. Moreover, we recreated the injury in vitro performing the procedure of oxygen-glucose deprivation on rat neonatal OPCs to determine its effect on cell viability, proliferation, and differentiation. In the in vivo model, MRI evaluation revealed changes in the volume of different brain regions, as well as changes in the directional diffusivity of water in brain tissue that may suggest pathological changes to myelinated neuronal fibers. Hypomyelination was observed in the cortex, striatum, and CA3 region of the hippocampus. Severe changes to myelin ultrastructure were observed, including delamination of myelin sheets. Interestingly, shortly after the injury, an increase in oligodendrocyte proliferation was observed, followed by an overproduction of myelin proteins 4 weeks after HI. Results verified with the in vitro model indicate, that in the first days after damage, OPCs do not show reduced viability, intensively proliferate, and overexpress myelin proteins and oligodendrocyte-specific transcription factors. In conclusion, despite the increase in oligodendrocyte proliferation and myelin protein expression after HI, the production of functional myelin sheaths in brain tissue is impaired. Presented study provides a detailed description of oligodendrocyte pathophysiology developed in an effect of HI injury, resulting in an altered CNS myelination. The described models may serve as useful tools for searching and testing effective of effective myelination-supporting therapies for HI injuries.

Neuronal autosis is Na+/K+-ATPase alpha 3-dependent and involved in hypoxic-ischemic neuronal death

Macroautophagy (hereafter called autophagy) is an essential physiological process of degradation of organelles and long-lived proteins. The discovery of autosis, a Na+/K+-ATPase (ATP1)-dependent type of autophagic cell death with specific morphological and biochemical features, has strongly contributed to the acceptance of a pro-death role of autophagy. However, the occurrence and relevance of autosis in neurons has never been clearly investigated, whereas we previously provided evidence that autophagy mechanisms could be involved in neuronal death in different in vitro and in vivo rodent models of hypoxia-ischemia (HI) and that morphological features of autosis were observed in dying neurons following rat perinatal cerebral HI. In the present study, we demonstrated that neuronal autosis could occur in primary cortical neurons using two different stimulations enhancing autophagy flux and neuronal death: a neurotoxic concentration of Tat-BECN1 (an autophagy-inducing peptide) and a hypoxic/excitotoxic stimulus (mimicking neuronal death induced by cerebral HI). Both stimulations induce autophagic neuronal death (dependent on canonical autophagic genes and independent on apoptotic, necroptotic or ferroptotic pathways) with all morphological and biochemical (ATP1a-dependent) features of autosis. However, we demonstrated that autosis is not dependent on the ubiquitous subunit ATP1a1 in neurons, as in dividing cell types, but on the neuronal specific ATP1a3 subunit. We also provided evidence that, in different in vitro and in vivo models where autosis is induced, ATP1a3-BECN1 interaction is increased and prevented by cardiac glycosides treatment. Interestingly, an increase in ATP1a3-BECN1 interaction is also detected in dying neurons in the autoptic brains of human newborns with severe hypoxic-ischemic encephalopathy (HIE). Altogether, these results suggest that ATP1a3-BECN1-dependent autosis could play an important role in neuronal death in HI conditions, paving the way for the development of new neuroprotective strategies in hypoxic-ischemic conditions including in severe case of human HIE.

Akt/mTOR Pathway Agonist SC79 Inhibits Autophagy and Apoptosis of Oligodendrocyte Precursor Cells Associated with Neonatal White Matter Dysplasia

White matter dysplasia (WMD) in preterm infants due to intrauterine inflammation is caused by excessive apoptosis of oligodendrocyte precursor cells (OPCs). In recent years, studies have found that excessive autophagy and apoptosis are highly interconnected and important in infection and inflammatory diseases in general. Therefore, in this study, we aimed to confirm whether regulation of autophagy by using the Akt phosphorylation agonist SC79 can inhibit abnormal apoptosis of OPCs and promote myelin maturation and white matter development in neonatal rats with WMD. We investigated the effect of inflammation on oligodendrocyte development in P0 neonatal rats by intracerebellar injection of LPS, and collected brain tissue at P2 and P5. Immunohistochemical and immunofluorescence staining were used to evaluate white matter damage, while immunofluorescence staining, terminal deoxynucleotidyl transferase dUTP nick end labeling analysis (TUNEL), and western blotting were used to evaluate autophagy and apoptosis. First, we observed that white matter development was arrested and white matter fiber maturation was impaired in LPS-inflicted pups compared with those in the sham-operated group. Second, treatment with SC79 reduced the levels of LC3II, caspase 3, caspase 9, and Bax/Bcl-2 and increased the levels of p62, p-Akt, and p-mTOR in the brain tissue of neonatal rats. Finally, SC79 treatment inhibited OPC apoptosis by increasing the binding of Beclin 1 to Bcl-2, which promoted OPC differentiation and maturation. However, the opposite results were observed after rapamycin administration. Taken together, our results suggest that SC79 can inhibit the abnormal apoptosis of OPCs caused by excessive autophagy through the Akt/mTOR pathway and that SC79 is a potential therapeutic agent for WMD in preterm infants.

Protective mechanisms of quercetin in neonatal rat brain injury induced by hypoxic-ischemic brain damage (HIBD)

Neonatal hypoxic-ischemic brain damage (HIBD) is a leading cause of infant mortality worldwide. This study explored whether quercetin (Que) exerts neuroprotective effects in a rat model of HIBD. A total of 36 seven-day-old Sprague-Dawley rats were divided into control, Que, HI, and HI + Que groups. The Rice method was used to establish HIBD in HI and HI + Que rats, which were treated with hypoxia (oxygen concentration of 8%) for 2 h after ligation of the left common carotid artery. The rats in the HI + Que group were intraperitoneally injected with Que (30 mg/kg) 1 h before hypoxia, and the rats in the Que group were only injected with the same amount of Que. Brain tissues were harvested 24 h postoperation and assessed by hematoxylin and eosin staining, 2,3,5-triphenyltetrazolium chloride staining, and terminal deoxynucleotidyl transferase dUTP nick-end labeling assay; relative gene and protein levels were evaluated by RT-qPCR, IHC, or western blot (WB) assay. Brain tissue morphologies were characterized by transmission electron microscopy (TEM); LC3B protein levels were assessed by immunofluorescence staining. Escape latencies and platform crossing times were significantly improved (p < .05) in HI + Que groups; infarct volume significantly decreased (p < .001), whereas the numbers of autophagic bodies and apoptotic cells increased and decreased, respectively. Meanwhile, NLRX1, ATG7, and Beclin1 expressions were significantly upregulated, and mTOR and TIM23 expressions, LC3B protein level, and LC 3II/LC 3I ratio were significantly downregulated. Que exerted neuroprotective effects in a rat model of HIBD by regulating NLRX1 and autophagy.

TMEM175 downregulation participates in impairment of the autophagy related lysosomal dynamics following neonatal hypoxic-ischemic brain injury

The mechanism underlying long-term cognitive impairment caused by neonatal hypoxic-ischemic brain injury (HIBI) remains unclear. Autophagy is a closely related mechanism and may play a role in this process. We aimed to investigate the role of lysosomal transmembrane protein 175 (TMEM175) in the autophagy-lysosome pathway in neonatal rats with HIBI. A neonatal rat model of HIBI was established, hypoxia was induced, followed by left common carotid artery ligation. Expression levels of TMEM175 and the corresponding proteins involved in autophagy flux and the endolysosomal system fusion process were measured. Rats were administered TMEM175 plasmid via intracerebroventricular injection to induce overexpression. Brain damage and cognitive function were then assessed. TMEM175 was downregulated in the hippocampal tissue, and the autophagy-lysosome pathway was impaired following HIBI in neonatal rats. Overexpression of TMEM175 significantly mitigated neuronal injury and improved long-term cognitive and memory function in neonatal rats with HIBI. We found that improvement in the autophagy-lysosome pathway and endolysosomal system homeostasis, which are TMEM175 related, occurred via regulation of lysosomal membrane dynamic fusion. TMEM175 plays a critical role in maintaining the autophagy-lysosome pathway and endolysosomal homeostasis, contributing to the amelioration of neuronal injury and impaired long-term cognitive function following neonatal HIBI.

Capsaicin attenuates excitotoxic-induced neonatal brain injury and brain mast cell-mediated neuroinflammation in newborn rats

Excitotoxicity and neuroinflammation are key contributors to perinatal brain injuries. Capsaicin, an active ingredient of chili peppers, is a potent exogenous agonist for transient receptor potential vanilloid 1 receptors. Although the neuroprotective and anti-inflammatory effects of capsaicin are well-documented, its effects on excitotoxic-induced neonatal brain injury and neuroinflammation have not previously been investigated. The aim of this study was to investigate the effects of capsaicin on brain damage, brain mast cells, and inflammatory mediators in a model of ibotenate-induced excitotoxic brain injury in neonatal rats. P5 rat-pups were intraperitoneally injected with vehicle, 0.2-, 1-, and 5-mg/kg doses of capsaicin, or the NMDA (N-methyl-d-aspartate) receptor antagonist MK-801 (dizocilpine), 30 min before intracerebral injection of 10 μg ibotenate. The naive-control group received no substance administration. The rat pups were sacrificed one or five days after ibotenate injection. Levels of activin A and interleukin (IL)-1β, IL-6, and IL-10 in brain tissue were measured using the enzyme-linked immunosorbent assay method. Cortex and white matter thicknesses, white matter lesion size, and mast cells were evaluated in brain sections stained with cresyl-violet or toluidine-blue. Capsaicin improved ibotenate-induced white matter lesions and cerebral white and gray matter thicknesses in a dose-dependent manner. In addition, it suppressed the degranulation and increased number of brain mast cells induced by ibotenate. Capsaicin also reduced the excitotoxic-induced production of neuronal survival factor activin A and of the pro-inflammatory cytokines IL-1β, and IL-6 in brain tissue. However, IL-10 levels were not altered by the treatments. MK-801, as a positive control, reversed all these ibotenate-induced changes, further confirming the success of the model. Our findings provide, for the first time, evidence for the therapeutic effects of capsaicin against excitotoxic-induced neonatal brain injury and brain mast cell-mediated neuroinflammation. Capsaicin may therefore be a promising candidate in the prevention and/or reduction of neonatal brain damage.

The protective effect of inhibiting mitochondrial fission on the juvenile rat brain following PTZ kindling through inhibiting the BCL2L13/LC3 mitophagy pathway

Maintaining the balance of mitochondrial fission and mitochondrial autophagy on seizures is helpful to find a solution to control seizures and reduce brain injuries. The present study is to investigate the protective effect of inhibiting mitochondrial fission on brain injury in juvenile rat epilepsy induced by pentatetrazol (PTZ) by inhibiting the BCL2L13/LC3-mediated mitophagy pathway. PTZ was injected (40 mg/kg) to induce kindling once every other day, for a total of 15 times. In the PTZ + DMSO (DMSO), PTZ + Mdivi-1 (Mdivi-1), and PTZ + WY14643 (WY14643) groups, rats were pretreated with DMSO, Mdivi-1 and WY14643 for half an hour prior to PTZ injection. The seizure attacks of young rats were observed for 30 min after model establishment. The Morris water maze (MWM) was used to test the cognition of experimental rats. After the test, the numbers of NeuN(+) neurons and GFAP(+) astrocytes were observed and counted by immunofluorescence (IF). The protein expression levels of Drp1, BCL2L13, LC3 and caspase 3 in the hippocampus of young rats were detected by immunohistochemistry (IHC) and Western blotting (WB). Compared with the PTZ and DMSO groups, the seizure latency in the Mdivi-1 group was longer (P < 0.01), and the severity degree and frequency of seizures were lower (P < 0.01). The MWM test showed that the incubation periods of crossing the platform in the Mdivi-1 group was significantly shorter. The number of platform crossings, the platform stay time, and the ratio of residence time/total stay time were significantly increased in the Mdivi-1 group (P < 0.01). The IF results showed that the number of NeuN(+) neurons in the Mdivi-1 group was greater, while the number of GFAP(+) astrocytes was lower. IHC and WB showed that the average optical density (AOD) and relative protein expression levels of Drp1, BCL2L13, LC3 and caspase 3 in the hippocampi of rats in the Mdivi-1 group were higher (P < 0.05). The above results in the WY14643 group were opposite to those in the Mdivi-1 group. Inhibition of mitochondrial fission could reduce seizure attacks, protect injured neurons, and improve cognition following PTZ-induced epilepsy by inhibiting mitochondrial autophagy mediated by the BCL2L13/LC3 mitophagy pathway.

Excitotoxicity, calcium and mitochondria: a triad in synaptic neurodegeneration

Glutamate is the most commonly engaged neurotransmitter in the mammalian central nervous system, acting to mediate excitatory neurotransmission. However, high levels of glutamatergic input elicit excitotoxicity, contributing to neuronal cell death following acute brain injuries such as stroke and trauma. While excitotoxic cell death has also been implicated in some neurodegenerative disease models, the role of acute apoptotic cell death remains controversial in the setting of chronic neurodegeneration. Nevertheless, it is clear that excitatory synaptic dysregulation contributes to neurodegeneration, as evidenced by protective effects of partial N-methyl-D-aspartate receptor antagonists. Here, we review evidence for sublethal excitatory injuries in relation to neurodegeneration associated with Parkinson's disease, Alzheimer's disease, amyotrophic lateral sclerosis and Huntington's disease. In contrast to classic excitotoxicity, emerging evidence implicates dysregulation of mitochondrial calcium handling in excitatory post-synaptic neurodegeneration. We discuss mechanisms that regulate mitochondrial calcium uptake and release, the impact of LRRK2, PINK1, Parkin, beta-amyloid and glucocerebrosidase on mitochondrial calcium transporters, and the role of autophagic mitochondrial loss in axodendritic shrinkage. Finally, we discuss strategies for normalizing the flux of calcium into and out of the mitochondrial matrix, thereby preventing mitochondrial calcium toxicity and excitotoxic dendritic loss. While the mechanisms that underlie increased uptake or decreased release of mitochondrial calcium vary in different model systems, a common set of strategies to normalize mitochondrial calcium flux can prevent excitatory mitochondrial toxicity and may be neuroprotective in multiple disease contexts.

The Reduction of Tau Hyperphosphorylation by Cornel Iridoid Glycosides Is Mediated by Their Influence on Calpain Activity

Alzheimer’s disease (AD) is the most common type of dementia, and the abnormal hyperphosphorylation of the tau protein is the main component of its pathogenesis. Calpain was found to be abnormally activated in neurofibrillary tangles (NFTs) in a previous report. Cornel iridoid glycosides (CIG) have been reported to reduce the hyperphosphorylation of tau protein. Nevertheless, the role of calpain in the reduction tau hyperphosphorylation by CIG remains unclear. In the present study, we investigated the effect of CIG on calpain activity through in vitro and in vivo experiments. Western blotting results suggested that CIG decreased the phosphorylation of tau at Ser 404 and Ser 262 sites in P301S mice. Moreover, CIG inhibited the activity of calpain and glycogen synthase kinase 3β (GSK-3β) and enhanced the activity of protein phosphatase 2A (PP2A) both in vivo and in vitro. CIG also inhibited the activation of PP2A and reduced the GSK-3β activity caused by the calpain activator dibucaine. In addition, the main components of CIG, morroniside and loganin, play an equivalent role in reducing calpain activity, as the effect of their combined use is equivalent to that of CIG. The abovementioned findings revealed that CIG improved PP2A activity and reduced GSK-3β activity by adjusting the activity of calpain 1, leading to a reduction in the phosphorylation of tau. This study highlights the remarkable therapeutic potential of CIG for managing AD.

Delivering progranulin to neuronal lysosomes protects against excitotoxicity

Loss-of-function mutations in progranulin (GRN) are a major genetic cause of frontotemporal dementia (FTD), possibly due to loss of progranulin’s neurotrophic and anti-inflammatory effects. Progranulin promotes neuronal growth and protects against excitotoxicity and other forms of injury. It is unclear if these neurotrophic effects are mediated through cellular signaling or through promotion of lysosomal function. Progranulin is a secreted proprotein that may activate neurotrophic signaling through cell-surface receptors. However, progranulin is efficiently trafficked to lysosomes and is necessary for maintaining lysosomal function. To determine which of these mechanisms mediates progranulin’s protection against excitotoxicity, we generated lentiviral vectors expressing progranulin (PGRN) or lysosome-targeted progranulin (L-PGRN). L-PGRN was generated by fusing the LAMP-1 transmembrane and cytosolic domains to the C-terminus of progranulin. L-PGRN exhibited no detectable secretion, but was delivered to lysosomes and processed into granulins. PGRN and L-PGRN protected against NMDA excitotoxicity in rat primary cortical neurons, but L-PGRN had more consistent protective effects than PGRN. L-PGRN’s protective effects were likely mediated through the autophagy-lysosomal pathway. In control neurons, an excitotoxic dose of NMDA stimulated autophagy, and inhibiting autophagy with 3-methyladenine reduced excitotoxic cell death. L-PGRN blunted the autophagic response to NMDA and occluded the protective effect of 3-methyladenine. This was not due to a general impairment of autophagy, as L-PGRN increased basal autophagy and did not alter autophagy after nutrient starvation. These data show that progranulin’s protection against excitotoxicity does not require extracellular progranulin, but is mediated through lysosomes, providing a mechanistic link between progranulin’s lysosomal and neurotrophic effects.

White matter injury in the neonatal hypoxic-ischemic brain and potential therapies targeting microglia

Neonatal hypoxic-ischemic (H-I) injury, which mainly causes neuronal damage and white matter injury (WMI), is among the predominant causes of infant morbidity (cerebral palsy, cognitive and persistent motor disabilities) and mortality. Disruptions to the oxygen and blood supply in the perinatal brain affect the cerebral microenvironment and may affect microglial activation, excitotoxicity, and oxidative stress. Microglia are significantly associated with axonal damage and myelinating oligodendrocytes, which are major pathological components of WMI. However, the effects of H-I injury on microglial functions and underlying transformation mechanisms remain poorly understood. The historical perception that these cells are major risk factors for ischemic stroke has been questioned due to our improved understanding of the diversity of microglial phenotypes and their alterable functions, which exacerbate or attenuate injuries in different regions in response to environmental instability. Unfortunately, although therapeutic hypothermia is an efficient treatment, death and disability remain the prognosis for a large proportion of neonates with H-I injury. Hence, novel neuroprotective therapies to treat WMI following H-I injury are urgently needed. Here, we review microglial mechanisms that might occur in the developing brain due to neonatal H-I injury and discuss whether microglia function as a double-edged sword in WMI. Then, we emphasize microglial heterogeneity, notably at the single-cell level, and sex-specific effects on the etiology of neurological diseases. Finally, we discuss current knowledge of strategies aiming to improve microglia modulation and remyelination following neonatal H-I injury. Overall, microglia-targeted therapy might provide novel and valuable insights into the treatment of neonatal H-I insult.

Treatment with the Ketone Body D-β-hydroxybutyrate Attenuates Autophagy Activated by NMDA and Reduces Excitotoxic Neuronal Damage in the Rat Striatum In Vivo

BACKGROUND

The ketone bodies (KB), β-hydroxybutyrate (BHB) and acetoacetate, have been proposed for the treatment of acute and chronic neurological disorders, however, the molecular mechanisms involved in KB protection are not well understood. KB can substitute for glucose and support mitochondrial metabolism increasing cell survival. We have reported that the D-isomer of BHB (D-BHB) stimulates autophagic degradation during glucose deprivation in cultured neurons increasing cell viability. Autophagy is a lysosomal degradation process of damaged proteins and organelles activated during nutrient deprivation to obtain building blocks and energy. However, impaired or excessive autophagy can contribute to neuronal death.

OBJECTIVE

The aim of the present study was to test whether D-BHB can preserve autophagic function in an in vivo model of excitotoxic damage induced by the administration of the glutamate receptor agonist, N-methyl-Daspartate (NMDA), in the rat striatum.

METHODS

D-BHB was administered through an intravenous injection followed by either an intraperitoneal injection (i.v+i.p) or a continuous epidural infusion (i.v+pump), or through a continuous infusion of D-BHB alone. Changes in the autophagy proteins ATG7, ATG5, BECLIN 1 (BECN1), LC3, Sequestrosome1/p62 (SQSTM1/ p62) and the lysosomal membrane protein LAMP2, were evaluated by immunoblot. The lesion volume was measured in cresyl violet-stained brain sections.

RESULTS

Autophagy is activated early after NMDA injection but autophagic degradation is impaired due to the cleavage of LAMP2. Twenty-four h after NMDA intrastriatal injection, the autophagic flux is re-established, but LAMP2 cleavage is still observed. The administration of D-BHB through the i.v+pump protocol reduced the content of autophagic proteins and the cleavage of LAMP2, suggesting decreased autophagosome formation and lysosomal membrane preservation, improving autophagic degradation. D-BHB also reduced brain injury. The i.v+i.p administration protocol and the infusion of D-BHB alone showed no effect on autophagy activation or degradation.

Autophagy in trimethyltin-induced neurodegeneration

Autophagy is a degradative process playing an important role in removing misfolded or aggregated proteins, clearing damaged organelles, such as mitochondria and endoplasmic reticulum, as well as eliminating intracellular pathogens. The autophagic process is important for balancing sources of energy at critical developmental stages and in response to nutrient stress. Recently, autophagy has been involved in the pathophysiology of neurodegenerative diseases although its beneficial (pro-survival) or detrimental (pro-death) role remains controversial. In the present review, we discuss the role of autophagy following intoxication with trimethyltin (TMT), an organotin compound that induces severe hippocampal neurodegeneration associated with astrocyte and microglia activation. TMT is considered a useful tool to study the molecular mechanisms occurring in human neurodegenerative diseases such as Alzheimer's disease and temporal lobe epilepsy. This is also relevant in the field of environmental safety, since organotin compounds are used as heat stabilizers in polyvinyl chloride polymers, industrial and agricultural biocides, and as industrial chemical catalysts.

Novel neuroprotective therapy with NeuroHeal by autophagy induction for damaged neonatal motoneurons

Rationale: Protective mechanisms allow healthy neurons to cope with diverse stresses. Excessive damage as well as aging can lead to defective functioning of these mechanisms. We recently designed NeuroHeal using artificial intelligence with the goal of bolstering endogenous neuroprotective mechanisms. Understanding the key nodes involved in neuroprotection will allow us to identify even more effective strategies for treatment of neurodegenerative diseases.

Methods: We used a model of peripheral nerve axotomy in rat pups, that induces retrograde apoptotic death of motoneurons. Nourishing mothers received treatment with vehicle, NeuroHeal or NeuroHeal plus nicotinamide, an inhibitor of sirtuins, and analysis of the pups were performed by immunohistochemistry, electron microscopy, and immunoblotting. In vitro, the post-translational status of proteins of interest was detailed using organotypic spinal cord cultures and genetic modifications in cell lines to unravel the neuroprotective mechanisms involved.

Results: We found that the concomitant activation of the NAD⁺-dependent deacetylase SIRT1 and the PI3K/AKT signaling pathway converge to increase the presence of deacetylated and phosphorylated FOXO3a, a transcription factor, in the nucleus. This favors the activation of autophagy, a pro-survival process, and prevents pro-apoptotic PARP1/2 cleavage.

Major conclusion: NeuroHeal is a neuroprotective agent for neonatal motoneurons that fine-tunes autophagy on by converging SIRT1/AKT/FOXO3a axis. NeuroHeal is a combo of repurposed drugs that allow its readiness for prospective pediatric use.

Current Evidence on Cell Death in Preterm Brain Injury in Human and Preclinical Models

Despite tremendous advances in neonatal intensive care over the past 20 years, prematurity carries a high burden of neurological morbidity lasting lifelong. The term encephalopathy of prematurity (EoP) coined by Volpe in 2009 encompasses all aspects of the now known effects of prematurity on the immature brain, including altered and disturbed development as well as specific lesional hallmarks. Understanding the way cells are damaged is crucial to design brain protective strategies, and in this purpose, preclinical models largely contribute to improve the comprehension of the cell death mechanisms. While neuronal cell death has been deeply investigated and characterized in (hypoxic–ischemic) encephalopathy of the newborn at term, little is known about the types of cell death occurring in preterm brain injury. Three main different morphological cell death types are observed in the immature brain, specifically in models of hypoxic–ischemic encephalopathy, namely, necrotic, apoptotic, and autophagic cell death. Features of all three types may be present in the same dying neuron. In preterm brain injury, description of cell death types is sparse, and cell loss primarily concerns immature oligodendrocytes and, infrequently, neurons. In the present review, we first shortly discuss the different main severe preterm brain injury conditions that have been reported to involve cell death, including periventricular leucomalacia (PVL), diffuse white matter injury (dWMI), and intraventricular hemorrhages, as well as potentially harmful iatrogenic conditions linked to premature birth (anesthesia and caffeine therapy). Then, we present an overview of current evidence concerning cell death in both clinical human tissue data and preclinical models by focusing on studies investigating the presence of cell death allowing discriminating between the types of cell death involved. We conclude that, to improve brain protective strategies, not only apoptosis but also other cell death (such as regulated necrotic and autophagic) pathways now need to be investigated together in order to consider all cell death mechanisms involved in the pathogenesis of preterm brain damage.

Autophagy is Activated In Vivo during Trimethyltin-Induced Apoptotic Neurodegeneration: A Study in the Rat Hippocampus

Trimethyltin (TMT) is an organotin compound known to produce significant and selective neuronal degeneration and reactive astrogliosis in the rodent central nervous system. Autophagy is the main cellular mechanism for degrading and recycling protein aggregates and damaged organelles, which in different stress conditions, such as starvation, generally improves cell survival. Autophagy is documented in several pathologic conditions, including neurodegenerative diseases. This study aimed to investigate the autophagy and apoptosis signaling pathways in hippocampal neurons of TMT-treated (Wistar) rats to explore molecular mechanisms involved in toxicant-induced neuronal injury. The microtubule-associated protein light chain (LC3, autophagosome marker) and sequestosome1 (SQSTM1/p62) (substrate of autophagy-mediated degradation) expressions were examined by Western blotting at different time points after intoxication. The results demonstrate that the LC3 II/I ratio significantly increased at 3 and 5 days, and that p62 levels significantly decreased at 7 and 14 days. Immunofluorescence images of LC3/neuronal nuclear antigen (NeuN) showed numerous strongly positive LC3 neurons throughout the hippocampus at 3 and 5 days. The terminal deoxynucleotidyltransferase dUTP nick end labeling (TUNEL) assay indicated an increase in apoptotic cells starting from 5 days after treatment. In order to clarify apoptotic pathway, immunofluorescence images of apoptosis-inducing factor (AIF)/NeuN did not show nuclear translocation of AIF in neurons. Increased expression of cleaved Caspase-3 was revealed at 5-14 days in all hippocampal regions by Western blotting and immunohistochemistry analyses. These data clearly demonstrate that TMT intoxication induces a marked increase in both autophagy and caspase-dependent apoptosis, and that autophagy occurring just before apoptosis could have a potential role in neuronal loss in this experimental model of neurodegeneration.

Autophagy-Related Gene 7 Polymorphisms and Cerebral Palsy in Chinese Infants

Cerebral palsy (CP) is a group of non-progressive motor impairment syndromes that are secondary to brain injury in the early stages of brain development. Numerous etiologies and risk factors of CP have been reported, and genetic contributions have recently been identified. Autophagy has an important role in brain development and pathological process, and autophagy-related gene 7 (ATG7) is essential for autophagosome biogenesis. The purpose of this study was to investigate the genetic association between ATG7 gene single nucleotide polymorphisms (SNPs) and CP in Han Chinese children. Six SNPs (rs346078, rs1470612, rs11706903, rs2606750, rs2594972, and rs4684787) were genotyped in 715 CP patients and 658 healthy controls using the MassArray platform. Plasma ATG7 protein was determined in 73 CP patients and 79 healthy controls. The differences in the allele and genotype frequencies of the rs1470612 and rs2594972 SNPs were determined between the CP patients and controls (p _allele = 0.02 and 0.0004, p _genotype = 0.044 and 0.0012, respectively). Subgroup analysis revealed a more significant association of rs1470612 (p _allele = 0.004, p _genotype = 0.0036) and rs2594972 (p _allele = 0.0004, p _genotype < 0.0001) with male CP, and more significant differences in allele and genotype frequencies were also noticed between CP patients with spastic diplegia and controls for rs1470612 (p _allele = 0.0024, p _genotype = 0.008) and rs2594972 (p _allele < 0.0001, p _genotype = 0.006). The plasma ATG7 level was higher in CP patients compared to the controls (10.58 ± 0.85 vs. 8.18 ± 0.64 pg/mL, p = 0.024). The luciferase reporter gene assay showed that the T allele of rs2594972 SNP could significantly increase transcriptional activity of the ATG7 promoter compared to the C allele (p = 0.009). These findings suggest that an association exists between genetic variants of ATG7 and susceptibility to CP, which provides novel evidence for the role of ATG7 in CP and contributes to our understanding of the molecular mechanisms of this neurodevelopmental disorder.

Activation of G-Protein-Coupled Receptor 30 Protects Neurons against Excitotoxicity through Inhibiting Excessive Autophagy Induced by Glutamate

Autophagy is a protecting intracellular pathway to transmit unnecessary or dysfunctional components to the lysosome for degeneration. Autophagic imbalance is connected with neurodegeneration. Neurodegenerative diseases including Parkinson's disease, Alzheimer's disease, and Huntington's disease are closely related to excitotoxicity and neuronal loss. Activation of G-protein-coupled receptor 30 (GPR30), an estrogen membrane receptor, protects neurons from excitotoxicity-induced cell death. However, whether autophagy is involved in the neuroprotective effect of GPR30 activation is not well-known. In this study, methyl thiazolyl tetrazolium (MTT), Western blot, monodansylcadaverine (MDC) staining, and immunofluorescent staining were employed to detect the role of autophagy in cultured primary cortical neurons after glutamate exposure and G1 treatment. Pretreatment of G1 (GPR30 specific agonist) reduced neuronal loss through inhibiting excessive autophagy induced by glutamate exposure, which was blocked by GPR30 antagonist G15, phosphatidylinositol-3-kinase (PI3K), and the mammalian target of rapamycin (mTOR) inhibitors. These data suggest that GPR30 protects neurons from cell loss primarily by modulating PI3K-AKT-mTOR signaling pathway. In addition, G1 alone did not affect the basal autophagy and cell viability. We conclude that GPR30 activation reduces glutamate-induced excessive autophagy in neurons and protects neurons against excitotoxicity.

Glutamate Transport and Preterm Brain Injury

Preterm birth complications are the leading cause of child death worldwide and a top global health priority. Among the survivors, the risk of life-long disabilities is high, including cerebral palsy and impairment of movement, cognition, and behavior. Understanding the molecular mechanisms of preterm brain injuries is at the core of future healthcare improvements. Glutamate excitotoxicity is a key mechanism in preterm brain injury, whereby the accumulation of extracellular glutamate damages the delicate immature oligodendrocytes and neurons, leading to the typical patterns of injury seen in the periventricular white matter. Glutamate excitotoxicity is thought to be induced by an interaction between environmental triggers of injury in the perinatal period, particularly cerebral hypoxia-ischemia and infection/inflammation, and developmental and genetic vulnerabilities. To avoid extracellular build-up of glutamate, the brain relies on rapid uptake by sodium-dependent glutamate transporters. Astrocytic excitatory amino acid transporter 2 (EAAT2) is responsible for up to 95% of glutamate clearance, and several lines of evidence suggest that it is essential for brain functioning. While in the adult EAAT2 is predominantly expressed by astrocytes, EAAT2 is transiently upregulated in the immature oligodendrocytes and selected neuronal populations during mid-late gestation, at the peak time for preterm brain injury. This developmental upregulation may interact with perinatal hypoxia-ischemia and infection/inflammation and contribute to the selective vulnerability of the immature oligodendrocytes and neurons in the preterm brain. Disruption of EAAT2 may involve not only altered expression but also impaired function with reversal of transport direction. Importantly, elevated EAAT2 levels have been found in the reactive astrocytes and macrophages of human infant post-mortem brains with severe white matter injury (cystic periventricular leukomalacia), potentially suggesting an adaptive mechanism against excitotoxicity. Interestingly, EAAT2 is suppressed in animal models of acute hypoxic-ischemic brain injury at term, pointing to an important and complex role in newborn brain injuries. Enhancement of EAAT2 expression and transport function is gathering attention as a potential therapeutic approach for a variety of adult disorders and awaits exploration in the context of the preterm brain injuries.

Identification and Characterization of Four Autophagy-Related Genes That Are Expressed in Response to Hypoxia in the Brain of the Oriental River Prawn (Macrobrachium nipponense)

Autophagy is a cytoprotective mechanism triggered in response to adverse environmental conditions. Herein, we investigated the autophagy process in the oriental river prawn (Macrobrachium nipponense) following hypoxia. Full-length cDNAs encoding autophagy-related genes (ATGs) ATG3, ATG4B, ATG5, and ATG9A were cloned, and transcription following hypoxia was explored in different tissues and developmental stages. The ATG3, ATG4B, ATG5, and ATG9A cDNAs include open reading frames encoding proteins of 319, 264, 268, and 828 amino acids, respectively. The four M. nipponense proteins clustered separately from vertebrate homologs in phylogenetic analysis. All four mRNAs were expressed in various tissues, with highest levels in brain and hepatopancreas. Hypoxia up-regulated all four mRNAs in a time-dependent manner. Thus, these genes may contribute to autophagy-based responses against hypoxia in M. nipponense. Biochemical analysis revealed that hypoxia stimulated anaerobic metabolism in the brain tissue. Furthermore, in situ hybridization experiments revealed that ATG4B was mainly expressed in the secretory and astrocyte cells of the brain. Silencing of ATG4B down-regulated ATG8 and decreased cell viability in juvenile prawn brains following hypoxia. Thus, autophagy is an adaptive response protecting against hypoxia in M. nipponense and possibly other crustaceans. Recombinant MnATG4B could interact with recombinant MnATG8, but the GST protein could not bind to MnATG8. These findings provide us with a better understanding of the fundamental mechanisms of autophagy in prawns.