Protein kinase Cβ2 inhibition reduces hyperglycemia-induced neural tube defects through suppression of a caspase 8-triggered apoptotic pathway

Tip60- and sirtuin 2-regulated MARCKS acetylation and phosphorylation are required for diabetic embryopathy

Failure of neural tube closure results in severe birth defects and can be induced by high glucose levels resulting from maternal diabetes. MARCKS is required for neural tube closure, but the regulation and of its biological activity and function have remained elusive. Here, we show that high maternal glucose induced MARCKS acetylation at lysine 165 by the acetyltransferase Tip60, which is a prerequisite for its phosphorylation, whereas Sirtuin 2 (SIRT2) deacetylated MARCKS. Phosphorylated MARCKS dissociates from organelles, leading to mitochondrial abnormalities and endoplasmic reticulum stress. Phosphorylation dead MARCKS (PD-MARCKS) reversed maternal diabetes-induced cellular organelle stress, apoptosis and delayed neurogenesis in the neuroepithelium and ameliorated neural tube defects. Restoring SIRT2 expression in the developing neuroepithelium exerted identical effects as those of PD-MARCKS. Our studies reveal a new regulatory mechanism for MARCKS acetylation and phosphorylation that disrupts neurulation under diabetic conditions by diminishing the cellular organelle protective effect of MARCKS.

Identification of Protein Kinase C Isoforms Involved in Type 1 Diabetic Encephalopathy in Mice

Diabetic encephalopathy is a complication of diabetes mellitus characterized by impaired cognitive functions. Protein kinase C (PKC) isoforms are rarely reported on diabetic encephalopathy, although they have been believed to play crucial roles in other diabetic complications. In this study, streptozotocin- (STZ-) induced diabetic mice were found to exhibit learning and memory deficits in the Morris water maze test. Meanwhile, the expression of cPKCβII, nPKCε, and cPKCγ did not change in the hippocampus, cortex, and striatum at 2 and 8 weeks after STZ injection. The nPKCε translocation to the membrane, where it is activated, was not altered in the above brain regions at 2 and 8 weeks after STZ injection. Nevertheless, cPKCβII translocation to the membrane was significantly decreased in the cortex and hippocampus at 8 weeks after STZ injection. The translocation of cPKCγ from the cytosol to the membrane was remarkably decreased in the hippocampus at 2 and 8 weeks and in the cortex and striatum at 8 weeks after STZ injection. In addition, deletion of cPKCγ aggravated the impairment of spatial learning and memory. In conclusion, our results suggest that the decrease in the activity of cPKCβII and cPKCγ, especially cPKCγ, may play key roles in the pathogenesis of diabetic encephalopathy.

Protein kinase C-alpha suppresses autophagy and induces neural tube defects via miR-129-2 in diabetic pregnancy

Gene deletion-induced autophagy deficiency leads to neural tube defects (NTDs), similar to those in diabetic pregnancy. Here we report the key autophagy regulators modulated by diabetes in the murine developing neuroepithelium. Diabetes predominantly leads to exencephaly, induces neuroepithelial cell apoptosis and suppresses autophagy in the forebrain and midbrain of NTD embryos. Deleting the Prkca gene, which encodes PKCα, reverses diabetes-induced autophagy impairment, cellular organelle stress and apoptosis, leading to an NTD reduction. PKCα increases the expression of miR-129-2, which is a negative regulator of autophagy. miR-129-2 represses autophagy by directly targeting PGC-1α, a positive regulator for mitochondrial function, which is disturbed by maternal diabetes. PGC-1α supports neurulation by stimulating autophagy in neuroepithelial cells. These findings identify two negative autophagy regulators, PKCα and miR-129-2, which mediate the teratogenicity of hyperglycaemia leading to NTDs. We also reveal a function for PGC-1α in embryonic development through promoting autophagy and ameliorating hyperglycaemia-induced NTDs.

Decoding the oxidative stress hypothesis in diabetic embryopathy through proapoptotic kinase signaling

Maternal diabetes-induced birth defects occur in 6-10% of babies born to mothers with pregestational diabetes, representing a significant maternal-fetal health problem. Currently, these congenital malformations represent a significant maternal-fetal medicine issue, but are likely to create an even greater public health threat as 3 million women of reproductive age (19-44 years) have diabetes in the United States alone, and this number is expected to double by 2030. Neural tube defects (NTDs) and congenital heart defects are the most common types of birth defects associated with maternal diabetes. Animal studies have revealed that embryos under hyperglycemic conditions exhibit high levels of oxidative stress resulting from enhanced production of reactive oxygen species and impaired antioxidant capability. Oxidative stress activates a set of proapoptotic kinase signaling intermediates leading to abnormal cell death in the embryonic neural tube, which causes NTD formation. Work in animal models also has revealed that maternal diabetes triggers a series of signaling intermediates: protein kinase C (PKC) isoforms, PKCα, βII and δ; apoptosis signal-regulating kinase 1; c-Jun-N-terminal kinase (JNK)1/2; caspase; and apoptosis. Specifically, maternal diabetes in rodent models activates the proapoptotic unfolded protein response and endoplasmic reticulum (ER) stress. A reciprocal causation between JNK1/2 activation and ER stress exists in diabetic embryopathy. Molecular studies further demonstrate that deletion of the genes for Prkc, Ask1, Jnk1, or Jnk2 abolishes maternal diabetes-induced neural progenitor apoptosis and ameliorates NTD formation. Similar preventive effects are also observed when apoptosis signal-regulating kinase 1, JNK1/2, or ER stress is inhibited. Cell membrane stabilizers and antioxidant supplements are also effective in prevention of diabetes-induced birth defects. Mechanistic studies have revealed important insights into our understanding the cause of diabetic embryopathy and have provided a basis for future interventions against birth defects or other pregnancy complications associated with maternal diabetes. The knowledge of a molecular pathway map identified in animal studies has created unique opportunities to identify molecular targets for therapeutic intervention.

Genetic, epigenetic, and environmental contributions to neural tube closure

The formation of the embryonic brain and spinal cord begins as the neural plate bends to form the neural folds, which meet and adhere to close the neural tube. The neural ectoderm and surrounding tissues also coordinate proliferation, differentiation, and patterning. This highly orchestrated process is susceptible to disruption, leading to neural tube defects (NTDs), a common birth defect. Here, we highlight genetic and epigenetic contributions to neural tube closure. We describe an online database we created as a resource for researchers, geneticists, and clinicians. Neural tube closure is sensitive to environmental influences, and we discuss disruptive causes, preventative measures, and possible mechanisms. New technologies will move beyond candidate genes in small cohort studies toward unbiased discoveries in sporadic NTD cases. This will uncover the genetic complexity of NTDs and critical gene-gene interactions. Animal models can reveal the causative nature of genetic variants, the genetic interrelationships, and the mechanisms underlying environmental influences.

Vinyl chloride monomer (VCM) induces high occurrence of neural tube defects in embryonic mouse brain during neurulation

The aim of this study was to explore the direct embryonic teratogenicity of vinyl chloride monomer (VCM), especially the toxic effects on the early development of the nervous system and its underlying mechanisms. Pregnant mice at embryonic day 6.5 (E6.5) were injected with different doses of VCM (200, 400 and 600 mg/kg) and embryos were harvested at E10.5. Our results showed that doses higher than 400 mg/kg of VCM increased the incidence of malformed embryos, especially the neural tube defects (NTDs). In addition, high-dose of VCM decreased mitotic figure counts in the neuroepithelium and enhanced the percentage of cells in G0/G1 phase, while they were reduced in S phase. The more VCM was injected into mice, the fewer positive PCNA cells were seen and the more positive TUNEL cells were observed in the neuroepithelium. Moreover, significant increases in the levels of caspase-3 protein were observed in NTD embryos. Our results demonstrate that during early pregnancy, exposure to doses higher than 400 mg/kg of VCM increases the incidence of malformations and particularly the rate of NTDs. High-dose of VCM inhibits the proliferation of neural cells and induces cell apoptosis, leading to an imbalance in the ratio of proliferation and apoptosis. Meanwhile, the apoptosis of neuroepithelial cells might be accelerated by the activation of the caspase-3 pathway, and it might be a reason for NTDs.

Superoxide dismutase 1 overexpression in mice abolishes maternal diabetes-induced endoplasmic reticulum stress in diabetic embryopathy

OBJECTIVE

Both oxidative stress and endoplasmic reticulum stress (ER stress) are causal events in diabetic embryopathy. We tested whether oxidative stress causes ER stress.

STUDY DESIGN

Wild-type (WT) and superoxide dismutase 1 (SOD1)-overexpressing day 8.75 embryos from nondiabetic WT control with SOD1 transgenic male and diabetic WT female with SOD1 transgenic male were analyzed for ER stress markers: C/EBP-homologous protein (CHOP), calnexin, eukaryotic initiation factor 2α (eIF2α), protein kinase ribonucleic acid (RNA)-like ER kinase (PERK), binding immunoglobulin protein, protein disulfide isomerase family A member 3, kinases inositol-requiring protein-1α (IRE1α), and the X-box binding protein (XBP1) messenger RNA (mRNA) splicing.

RESULTS

Maternal diabetes significantly increased the levels of CHOP, calnexin, phosphorylated (p)-eIF2α, p-PERK, and p-IRE1α; triggered XBP1 mRNA splicing; and enhanced ER chaperone gene expression in WT embryos. SOD1 overexpression blocked these diabetes-induced ER stress markers.

CONCLUSION

Mitigating oxidative stress via SOD1 overexpression blocks maternal diabetes-induced ER stress in vivo.

New concepts in diabetic embryopathy

Diabetes mellitus is responsible for nearly 10% of fetal anomalies in diabetic pregnancies. Although aggressive perinatal care and glycemic control are available in developed countries, the birth defect rate in diabetic pregnancies remains higher than that in the general population. Major cellular activities (ie, proliferation and apoptosis) and intracellular metabolic conditions (ie, nitrosative, oxidative, and endoplasmic reticulum stress) have been shown to be associated with diabetic embryopathy using animal models. Translating advances made in animal studies into clinical applications in humans requires collaborative efforts across the basic research, preclinical, and clinical communities.

SOD1 suppresses maternal hyperglycemia-increased iNOS expression and consequent nitrosative stress in diabetic embryopathy

OBJECTIVE

Hyperglycemia induces oxidative stress and increases inducible nitric oxide synthase (iNOS) expression. We hypothesized that oxidative stress is responsible for hyperglycemia-induced iNOS expression.

STUDY DESIGN

iNOS-luciferase activities, nitrosylated protein, and lipid peroxidation markers 4-hydroxynonenal and malondialdehyde were determined in parietal yolk sac-2 cells exposed to 5 mmol/L glucose or high glucose (25 mmol/L) with or without copper zinc superoxide dismutase 1 (SOD1) treatment. Levels of iNOS protein and messenger RNA, nitrosylated protein, and cleaved caspase-3 and -8 were assessed in wild-type embryos and SOD1-overexpressing embryos from nondiabetic and diabetic dams.

RESULTS

SOD1 treatment diminished high glucose-induced oxidative stress, as evidenced by 4-hydroxynonenal and malondialdehyde reductions, and it blocked high glucose-increased iNOS expression, iNOS-luciferase activities, and nitrosylated protein. In vivo SOD1 overexpression suppressed hyperglycemia-increased iNOS expression and nitrosylated protein, and it blocked caspase-3 and -8 cleavage.

CONCLUSION

We conclude that oxidative stress induces iNOS expression, nitrosative stress, and apoptosis in diabetic embryopathy.

The essential role of protein kinase Cδ in diabetes-induced neural tube defects

BACKGROUND

Maternal diabetes causes neural tube defects (NTDs) in the embryos via activating protein kinase Cs (PKCs), which regulate programmed cell death (apoptosis). The aims of this study are to investigate the role of proapoptotic PKCδ in NTD formation and the underlying mechanisms.

METHODS

PKCδ heterozygous (pkcδ(+/-)) female mice were diabetic (DM) induced by intravenous injection of streptozotocin. Occurrence of NTDs was evaluated at embryonic day 11.5 and compared between wild type (WT) and PKCδ homozygous (pkcδ(-/-)) embryos. Changes in oxidative and endoplasmic reticulum (ER) stress-associated factors and stress-response c-Jun N-terminal kinases (JNKs) were assessed using Western blot assay.

RESULTS

Compared to DM/WT, the DM/PKCδ(-/-) embryos had significantly lower NTD rate and lower levels of oxidative and ER stress factors and JNK activation. These values were similar to those in the non-diabetic control group.

CONCLUSION

PKCδ plays a critical role in diabetes-induced NTDs, potentially through increasing oxidative and ER stress and JNK-associated stress-response pathways.

Diabetes-induced birth defects: what do we know? What can we do?

Birth defects are the leading cause of infant mortality in the United States, which has one of the highest infant mortality rates in the developed world. Many of these birth defects can be attributed to pre-existing, or pregestational, diabetes in pregnancy, which significantly increases a mother's risk of having a child with a major birth defect. Strict preconceptional and early pregnancy glucose control, supplementation with multivitamins and fatty acids, and lower glycemic dietary management have been shown to reduce the incidence of birth defects in experimental and epidemiologic studies. However, because more than half of pregnancies are unplanned, these methods are not generalizable across the population. Thus, better interventions are urgently needed. Based on what we know about the molecular pathophysiology of diabetic embryopathy, our laboratory and others are developing interventions against to key molecular targets in this multifactorial disease process.