High glucose induces apoptosis in embryonic neural progenitor cells by a pathway involving protein PKCδ

Metabolism navigates neural cell fate in development, aging and neurodegeneration

An uninterrupted energy supply is critical for the optimal functioning of all our organs, and in this regard the human brain is particularly energy dependent. The study of energy metabolic pathways is a major focus within neuroscience research, which is supported by genetic defects in the oxidative phosphorylation mechanism often contributing towards neurodevelopmental disorders and changes in glucose metabolism presenting as a hallmark feature in age-dependent neurodegenerative disorders. However, as recent studies have illuminated roles of cellular metabolism that span far beyond mere energetics, it would be valuable to first comprehend the physiological involvement of metabolic pathways in neural cell fate and function, and to subsequently reconstruct their impact on diseases of the brain. In this Review, we first discuss recent evidence that implies metabolism as a master regulator of cell identity during neural development. Additionally, we examine the cell type-dependent metabolic states present in the adult brain. As metabolic states have been studied extensively as crucial regulators of malignant transformation in cancer, we reveal how knowledge gained from the field of cancer has aided our understanding in how metabolism likewise controls neural fate determination and stability by directly wiring into the cellular epigenetic landscape. We further summarize research pertaining to the interplay between metabolic alterations and neurodevelopmental and psychiatric disorders, and expose how an improved understanding of metabolic cell fate control might assist in the development of new concepts to combat age-dependent neurodegenerative diseases, particularly Alzheimer's disease.

Maternal hyperglycemia disturbs neocortical neurogenesis via epigenetic regulation in C57BL/6J mice

Offspring of mothers with hyperglycemia during pregnancy have a higher incidence of long-term neuropsychiatric disorders than offspring from a normal pregnancy, indicating that neocortical neurogenesis might be affected by maternal hyperglycemia. A paucity of study evaluating the effects of hyperglycemia on neocortical neurogenetic differentiation of neural stem cells, and the mechanism remains unclear. We sought to investigate the the roles and possible molecular mechanism of maternal hyperglycemia on neocortical neurogenetic differentiation of neural stem cells. We established a mouse model of a hyperglycemic pregnancy to study effects of intrauterine exposure to maternal hyperglycemia on neocortical neurogenesis. We observed morphological changes in the neocortex and detected the neurogenetic differentiation of neural stem cells in offspring affected by high glucose levels. We investigated the regulatory network between epigenetic modification and transcription factors in differentiated neural stem cells under hyperglycemic conditions. Maternal hyperglycemia disturbs neocortical lamination in some non-malformed offspring. Our results suggested that hyperglycemia altered the early-born neuron fate and the distribution of newborn neurons in deep layers by promoting the earlier differentiation of neural stem cells. Altered histone acetylation and its regulation on the transcription of proneural genes might be correlated to the disrupted differentiation of neural stem cells and altered distribution of newborn projection neurons in the neocortex. Our data raised the possibility that maternal hyperglycemia in pregnancy disturbs the laminar distribution of neocortical projection neurons in some non-malformed offspring via epigenetic regulation on neural stem cell differentiation and the birthdate of neocortical neurons.

High salt-induced excess reactive oxygen species production resulted in heart tube malformation during gastrulation

An association has been proved between high salt consumption and cardiovascular mortality. In vertebrates, the heart is the first functional organ to be formed. However, it is not clear whether high-salt exposure has an adverse impact on cardiogenesis. Here we report high-salt exposure inhibited basement membrane breakdown by affecting RhoA, thus disturbing the expression of Slug/E-cadherin/N-cadherin/Laminin and interfering with mesoderm formation during the epithelial-mesenchymal transition(EMT). Furthermore, the DiI⁺ cell migration trajectory in vivo and scratch wound assays in vitro indicated that high-salt exposure restricted cell migration of cardiac progenitors, which was caused by the weaker cytoskeleton structure and unaltered corresponding adhesion junctions at HH7. Besides, down-regulation of GATA4/5/6, Nkx2.5, TBX5, and Mef2c and up-regulation of Wnt3a/β-catenin caused aberrant cardiomyocyte differentiation at HH7 and HH10. High-salt exposure also inhibited cell proliferation and promoted apoptosis. Most importantly, our study revealed that excessive reactive oxygen species(ROS)generated by high salt disturbed the expression of cardiac-related genes, detrimentally affecting the above process including EMT, cell migration, differentiation, cell proliferation and apoptosis, which is the major cause of malformation of heart tubes.

Melatonin prevents neural tube defects in the offspring of diabetic pregnancy

Melatonin, an endogenous neurohormone secreted by the pineal gland, has a variety of physiological functions and neuroprotective effects. However, its protective role on the neural tube defects (NTDs) was not very clear. The aim of this study was to investigate the effects of melatonin on the incidence of NTDs (including anencephaly, encephalocele, and spina bifida) of offspring from diabetic pregnant mice as well as its underlying mechanisms. Pregnant mice were given 10 mg/kg melatonin by daily i.p. injection from embryonic day (E) 0.5 until being killed on E11.5. Here, we showed that melatonin decreased the NTDs (especially exencephaly) rate of embryos exposed to maternal diabetes. Melatonin stimulated proliferation of neural stem cells (NSCs) under hyperglycemic condition through the extracellular regulated protein kinases (ERK) pathway. Furthermore, as a direct free radical scavenger, melatonin decreased apoptosis of NSCs exposed to hyperglycemia. In the light of these findings, it suggests that melatonin supplementation may play an important role in the prevention of neural malformations in diabetic pregnancy.

PKCδ promotes high glucose induced renal tubular oxidative damage via regulating activation and translocation of p66Shc

Diabetic kidney disease (DKD) is a leading cause of end-stage renal disease (ESRD). Renal tubular injury by overproduction of ROS in mitochondria plays a critical role in the pathogenesis of DKD. Evidences have shown that p66Shc was involved in renal tubular injury via mitochondrial-dependent ROS production pathway, but little is known about the upstream signaling of p66Shc that leads to tubular oxidative damage under high glucose conditions. In this study, an increased PKCδ and p66Shc activation and ROS production in renal tissues of patients with diabetic nephropathy were seen and further analysis revealed a positive correlation between the tubulointerstitial damage and p-PKCδ, p-p66Shc, and ROS production. In vitro, we investigated the phosphorylation and activation of p66Shc and PKCδ during treatment of HK-2 cells with high glucose (HG). Results showed that the activation of p66Shc and PKCδ was increased in a dose- and time-dependent manner, and this effect was suppressed by Rottlerin, a pharmacologic inhibitor of PKCδ. Moreover, PKCδ siRNA partially blocked HG-induced p66Shc phosphorylation, translocation, and ROS production in HK-2 cells. Taken together, these data suggest that activation of PKCδ promotes tubular cell injury through regulating p66Shc phosphorylation and mitochondrial translocation in HG ambient.

Protein kinase C δ (PKCδ) splice variants modulate apoptosis pathway in 3T3L1 cells during adipogenesis: identification of PKCδII inhibitor

Increased food intake and lack of physical activity results in excess energy stored in adipocytes, and this imbalance contributes to obesity. New adipocytes are required for storage of energy in the white adipose tissue. This process of adipogenesis is widely studied in differentiating 3T3L1 preadipocytes in vitro. We have identified a key signaling kinase, protein kinase C delta (PKCδ), whose alternative splice variant expression is modulated during adipogenesis. We demonstrate that PKCδII splice variant promotes survival in differentiating 3T3L1 cells through the Bcl2 pathway. Here we demonstrate that resveratrol, a naturally occurring polyphenol, increases apoptosis and inhibits adipogenesis along with disruption of PKCδ alternative splicing during 3T3L1 differentiation. Importantly, we have identified a PKCδII splice variant inhibitor. This inhibitor may be a valuable tool with therapeutic implications in obesity.

Oxidative Stress, DNA Damage, and c-Abl Signaling: At the Crossroad in Neurodegenerative Diseases?

The c-Abl tyrosine kinase is implicated in diverse cellular activities including growth factor signaling, cell adhesion, oxidative stress, and DNA damage response. Studies in mouse models have shown that the kinases of the c-Abl family play a role in the development of the central nervous system. Recent reports show that aberrant c-Abl activation causes neuroinflammation and neuronal loss in the forebrain of transgenic adult mice. In line with these observations, an increased c-Abl activation is reported in human neurodegenerative pathologies, such as Parkinson's, and Alzheimer's diseases. This suggests that aberrant nonspecific posttranslational modifications induced by c-Abl may contribute to fuel the recurrent phenotypes/features linked to neurodegenerative disorders, such as an impaired mitochondrial function, oxidative stress, and accumulation of protein aggregates. Herein, we review some reports on c-Abl function in neuronal cells and we propose that modulation of different aspects of c-Abl signaling may contribute to mediate the molecular events at the interface between stress signaling, metabolic regulation, and DNA damage. Finally, we propose that this may have an impact in the development of new therapeutic strategies.

Insulin promotes neuronal survival via the alternatively spliced protein kinase CδII isoform

Insulin signaling pathways in the brain regulate food uptake and memory and learning. Insulin and protein kinase C (PKC) pathways are integrated and function closely together. PKC activation in the brain is essential for learning and neuronal repair. Intranasal delivery of insulin to the central nervous system (CNS) has been shown to improve memory, reduce cerebral atrophy, and reverse neurodegeneration. However, the neuronal molecular mechanisms of these effects have not been studied in depth. PKCδ plays a central role in cell survival. Its splice variants, PKCδI and PKCδII, are switches that determine cell survival and fate. PKCδI promotes apoptosis, whereas PKCδII promotes survival. Here, we demonstrate that insulin promotes alternative splicing of PKCδII isoform in HT22 cells. The expression of PKCδI splice variant remains unchanged. Insulin increases PKCδII alternative splicing via the PI3K pathway. We further demonstrate that Akt kinase mediates phosphorylation of the splicing factor SC35 to promote PKCδII alternative splicing. Using overexpression and knockdown assays, we demonstrate that insulin increases expression of Bcl2 and bcl-xL via PKCδII. We demonstrate increased cell proliferation and increased BrdU incorporation in insulin-treated cells as well as in HT22 cells overexpressing PKCδII. Finally, we demonstrate in vivo that intranasal insulin promotes cognitive function in mice with concomitant increases in PKCδII expression in the hippocampus. This is the first report of insulin, generally considered a growth or metabolic hormone, regulating the alternative isoform expression of a key signaling kinase in neuronal cells such that it results in increased neuronal survival.