Demonstration of the essential role of protein kinase C isoforms in hyperglycemia-induced embryonic malformations

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.

Effect of PMA-induced protein kinase C activation on development and apoptosis in early zebrafish embryos

Protein kinase C (PKC) isoforms have been implicated in several key steps during early development, but the consequences of xenobiotic-induced PKC activation during early embryogenesis are still unknown. In this study, zebrafish embryos were exposed to a range of phorbol 12-myristate 13-acetate (PMA) concentrations (0-200μg/L) at different time points after fertilization. Results showed that 200μgPMA/L caused development of yolk bags, cardiac edema, slow blood flow, pulsating blood flow, slow pulse, elongated heart, lack of tail fins, curved tail, and coagulation. PMA exposure decreased survival rate of the embryos starting within the first 24h and becoming more pronounced after prolonged exposure (96h). PMA increased the number of apoptotic cells in the brain region as demonstrated by acridine orange staining and caused up-regulation of caspase 9 (casp9) and p53 up-regulated modulator of apoptosis (puma) mRNA in whole embryos. PMA caused oxidative stress in the embryos as demonstrated by decreased mRNA expression of catalase and superoxide dismutase 2. Inhibition of Pkc with GF109203X improved overall survival rate, reduced apoptosis in the brain and decreased expression of casp9 and puma in the PMA-exposed embryos. However, Pkc inhibition neither prevented development of deformities nor reversed oxidative stress in the PMA-exposed embryos. These data suggest that direct over-activation of Pkc during early embryogenesis of zebrafish is associated with apoptosis and decreased survival rate of the embryos.

Advances in revealing the molecular targets downstream of oxidative stress-induced proapoptotic kinase signaling in diabetic embryopathy

Preexisting maternal diabetes is a high-risk factor of diabetic embryopathy, such as neural tube defects and congenital heart defects. Maternal diabetes significantly increases the production of reactive oxygen species, resulting in oxidative stress and diabetic embryopathy. Multiple cellular and metabolic factors contribute to these processes. Forkhead box O (FoxO)-3a has been demonstrated as a key transcription factor in the signaling transduction pathways responsible for maternal diabetes-induced birth defects. Apoptosis signal-regulating kinase 1 (ASK1) activated by oxidative stress stimulates nuclear translocation of FoxO3a, resulting in the overexpression of tumor necrosis factor receptor 1-associated death domain protein, which, in turn, leads to caspase-8 activation and apoptosis. Maternal diabetes-activated c-Jun N-terminal kinase (JNK)-1/2, downstream effectors of ASK1, can be blocked by superoxide dismutase-1 overexpression, suggesting that oxidative stress is responsible for JNK1/2 signaling activation. Deletion of JNK1/2 significantly suppressed the activity of FoxO3a. These observations indicate that maternal diabetes-induced oxidative stress stimulates the activation of ASK1, JNK1/2, FoxO3a, tumor necrosis factor receptor 1-associated death domain protein, caspase-8 cleavage, and finally, apoptosis and diabetic embryopathy.

A novel association of biventricular cardiac noncompaction and diabetic embryopathy: case report and review of the literature

Diabetic embryopathy refers to a constellation of congenital malformations arising in the setting of poorly controlled maternal diabetes mellitus. Cardiac abnormalities are the most frequently observed findings, with a 5-fold risk over normal pregnancies. Although a diverse spectrum of cardiac defects has been documented, cardiac noncompaction morphology has not been associated with this syndrome. In this report, we describe a novel case of biventricular cardiac noncompaction in a neonate of a diabetic mother. The patient was a late preterm female with right anotia, caudal dysgenesis, multiple cardiac septal and aortic arch defects, and biventricular cardiac noncompaction. Examination of both ventricles demonstrated spongy myocardium with increased myocardial trabeculation greater than 50% left ventricular thickness and greater than 75% right ventricular thickness, with hypoplasia of the bilateral papillary muscles, consistent with noncompaction morphology. Review of the literature highlights the importance of gene expression and epigenomic regulation in cardiac embryogenesis.

Hyperglycemia induces embryopathy, even in the absence of systemic maternal diabetes: an in vivo test of the fuel mediated teratogenesis hypothesis

Embryonic exposure to excess circulating fuels is proposed to underlie diabetic embryopathy. To isolate the effects of hyperglycemia from the many systemic anomalies of diabetes, we infused 4 mg/min glucose into the left uterine artery of non-diabetic pregnant rats on gestation days (GD) 7-9. Right-sided embryos and dams exhibited no glucose elevation. Embryos were assessed on GD13, comparing the left versus right uterine horns. Hyperglycemic exposure increased rates of embryopathy, resorptions, and worsened embryopathy severity. By contrast, saline infusion did not affect any of these parameters. To assess for possible embryopathy susceptibility bias between uterine horns, separate dams were given retinoic acid (25mg/kg, a mildly embryopathic dose) systemically on GD7.5. The resultant embryopathy rates were equivalent between uterine horns. We conclude that hyperglycemia, even in the absence of systemic maternal diabetes, is sufficient to produce in vivo embryopathy during organogenesis.

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.

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.

SOD1 overexpression in vivo blocks hyperglycemia-induced specific PKC isoforms: substrate activation and consequent lipid peroxidation in diabetic embryopathy

OBJECTIVE

Oxidative stress plays a causative role in diabetic embryopathy. We tested whether mitigating oxidative stress, using superoxide dismutase 1 (SOD1) transgenic (Tg) mice, would block hyperglycemia-induced specific protein kinase C (PKC) isoform activation and its downstream cascade.

STUDY DESIGN

Day 8.5 embryos from nondiabetic wild-type control (NC), diabetic mellitus wild-type (DM), and diabetic SOD1-Tg mice (DM-SOD1-Tg) were used for detection of phosphorylated (p-) PKCα/βII and p-PKCδ, and levels of 2 prominent PKC substrates, phosphorylated myristoylated alanine-rich protein kinase C substrate (MARCKS) and receptor for activated C kinase 1 (RACK1), and lipid peroxidation markers, 4-hydroxynonenal (4-HNE) and malondialdehyde (MDA).

RESULTS

Levels of p-PKCα/βII, p-PKCδ, p-MARCKS, 4-HNE, and MDA were significantly elevated in the DM group compared with those in the NC group and the DM-SOD1-Tg group. The NC and DM-SOD1-Tg groups had comparable levels of these protein and lipid peroxidation markers. RACK1 levels did not differ among the 3 groups.

CONCLUSION

Mitigating oxidative stress by SOD1 overexpression blocks maternal hyperglycemia-induced activation of specific PKC isoforms and downstream cascades.

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

Diabetic-induced neural tube defects in embryos are caused by apoptosis of neural progenitor cells (NPCs); however, the underlying mechanisms are poorly understood. The present study is aimed to investigate the specific cellular proteins that may be involved in apoptosis of NPCs. We show here that hyperglycemia-induced apoptosis of NPCs was through a PKCδ-dependent mechanism. Tyrosine phosphorylation of PKCδ was required for PKCδ binding to c-Abl in the cytoplasm, and inhibition of c-Abl by STI571 or knock-down of c-Abl by RNAi decreased the phosphorylation of PKCδ. Moreover, translocation of PKCδ and c-Abl complex from the cytoplasm to the nucleus, was blocked by down-regulation of PKCδ or c-Abl. Furthermore, we found that interaction of PKCδ and c-Abl played a crucial role in p53 accumulation in the nucleus, which was linked to the apoptosis of NPCs in response to high glucose.

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

OBJECTIVE

Neural tube defects in diabetic embryopathy are associated with increased protein kinase C (PKC)β2 activity and programmed cell death (apoptosis). The apoptosis is triggered by caspase 8, which activates members of the Bcl-2 and caspase families, such as Bid and caspase 3. Whether PKCβ2 regulates caspase 8-induced apoptosis remains to be addressed.

STUDY DESIGN

Mouse embryos at embryonic day 8.5 were cultured in a high concentration of glucose (22 mmol/L) and treated with PKCβ2 inhibitor (50 nmol/L) for 48 hours. The levels of apoptosis and activation of apoptotic factors were quantified using the terminal deoxynucleotidyl transferase deoxyuridine triphosphate nick end labeling and Western blot assays, respectively.

RESULTS

Reduction in the rate of neural tube defect by PKCβ2 inhibition is associated with significant decreases in the levels of apoptosis, and caspase 8, caspase 3, and Bid activation, and cytochrome C release from mitochondria, to the similar levels as in euglycemic controls (8.3 mmol/L; P < .05).

CONCLUSION

PKCβ2 influences a caspase 8-regulated apoptotic pathway in diabetic embryopathy.

Cardiac malformations and alteration of TGFbeta signaling system in diabetic embryopathy

BACKGROUND

Cardiovascular defects are the most common anomalies in diabetic embryopathy. The mechanisms underlying the manifestation of the defects remain to be addressed.

METHODS

Female mice were administered streptozotocin to induce diabetes. Embryos from euglycemic (control) and hyperglycemic groups were examined for morphological and histological evaluation of malformations. Cell proliferation and programmed cell death (apoptosis) were assessed using mitotic markers (BrdU and Ki67) and TUNEL assay, respectively. Expression of eight four genes in the TGFbeta signaling system was analyzed using real-time RT-PCR.

RESULTS

Structural abnormalities were observed in the heart and neural tube in diabetic groups, with significantly higher malformation rates than in control groups. Moreover, malformation rates in the heart were higher than those in the neural tube. Cardiac abnormalities including dilated heart tube, smaller ventricles, conotruncal stenosis, and abnormal heart looping were seen during early morphogenesis prior to cardiac septation [embryonic day (E) 9.5-11.5]. Histological examinations showed hypoplastic myocardium and endocardial cushions. After cardiac septation (E15.5), ventricular septal defects were observed, which were manifested in the non-muscular portion of the septum. Significant decreases in cell proliferation with no differences in apoptosis were observed in the myocardium and endocardial cushions in diabetic compared to control groups. Factors in the TGFbeta signaling that regulate heart development were downregulated by maternal diabetes.

CONCLUSIONS

Maternal diabetes causes malformations in the heart of the embryo. The heart is more susceptible to maternal diabetic insults than the neural tube. Malformations in the heart prior to septation are associated with decreased cell proliferation, but not increased apoptosis. The TGFbeta signaling is involved in cardiac malformations in diabetic embryopathy.

Caspase-8: a key role in the pathogenesis of diabetic embryopathy

Maternal diabetes causes neural tube defects in embryos, which are associated with increased apoptosis in the neuroepithelium. Many factors, including effector caspases, have been shown to be involved in the events. However, the key regulators have not been identified and the underlying mechanisms remain to be addressed. Caspase-8, an initiator caspase, has been shown to be altered in diabetic embryopathy, suggesting a role as an upstream apoptotic regulator. Using mouse embryos as a model system, this study demonstrates that caspase-8 is required for the production of hyperglycemia-associated embryonic malformations. Caspase-8 was shown to be expressed in the developing neural tube. Its activity, as evidenced by enhanced cleavage, was increased by hyperglycemia. These changes were associated with increased formation of the active cleavage of Bid. Inhibition of caspase-8 activity in high glucose-challenged embryos reduced the rate of embryonic malformation and this was associated with decreased apoptosis in the neuroepithelium of the neural tube. Inhibition of caspase-8 activity also reduced hyperglycemia-induced Bid activation and caspase-9 cleavage. These data suggest that caspase-8 may control diabetic embryopathy-associated apoptosis via regulation of the Bid-stimulated mitochondrion/caspase-9 pathway.

[Differentially expressed genes in diabetes-induced embryopathy]

To determine molecular mechanism in hyperglycemia induced congenital neural tube defects, yolk sac cells were harvested at gestational day 12 from streptozotocin (STZ) -induced diabetic rats with congenital neural tube defects in offspring, STZ-induced diabetic rats without neural tube defects and normal control group. We analyzed gene expression profiles in yolk sac cells using a DNA microarray technique. Changes in apoptotic and MAP Kinase signaling pathways were detected by Western blotting analyses. Comparison of genes in yolk sac cells with a total of 1 200 genes in the control cells, 79 genes differently expressed between the two groups were detected. Forty-two of them were up-regulated and 37 were down-regulated. There was strong characteristic apoptotic DNA ladder in yolk sac cells in embryopathic offspring from experimentally-induced diabetic rats. The activity of ERK1/2 was dramatically decreased and the activity of JNK1/2 was significantly increased. Differentially expressed genes, MAP Kinase, and apoptotic signal pathways play very important roles in hyperglycemia induced neural tube defects. We hope that these could provide useful hallmark to rapid identification of early diabetic embryopathy.