Research

What we do in the lab

My research focuses on the molecular mechanism(s) and potential therapeutic approaches of maternal diabetes-induced neural tube defects and cardiovascular defects in the offspring. Currently, I am directing a multi-million NIH-funded research group. My laboratory has made original and significant contributions to the area of maternal diabetes-induced structural birth defects, particularly delineating the molecular mechanism(s) underlying neural tube defects and heart defects and revealing the therapeutic potential of several naturally occurring compounds. Specifically, we have been working the following areas:

1. Decoding the oxidative stress hypothesis in diabetic embryopathy through pro-apoptotic kinase signaling.

A decade ago, equipped with a wealth of signaling transduction knowledge, I began to look at the role of pro-apoptotic c-Jun-N-terminal kinase 1/2 (JNK1/2) signaling in diabetic embryopathy. Using the superoxide dismutase 1 (SOD1) Tg mice, we demonstrated that maternal diabetes-induced oxidative stress causes JNK1/2 activation. The JNK1/2 pharmacological inhibitor, SP600125, ameliorated, whereas the JNK1/2 activator, sorbitol, mimics high glucose-induced NTDs. Furthermore, using JNK1 and JNK2 knockout (KO) mice, we provided molecular evidence to support the hypothesis that JNK1/2 activation plays a causal role in the induction of neural tube defects (NTDs) in diabetic pregnancies. JNK1/2 activation leads to activation of transcription factors, c-Jun, ATF2, Elk1 and FoxO3a, caspase 3, 8, and neuroepithelial cell apoptosis. Thus, I was the first one to demonstrate the causality of JNK1/2 in diabetic embryopathy (Biochem Biophys Res Commun 2007; Am J Obstet Gynecol 2008a, b, 2010, 2015; Diabetes 2012).

Impact: My laboratory is among the first to establish a mouse model of diabetic embryopathy. Using genetically modified mice, my group revealed the causal role of JNK1/2 in the induction of neural tube defects in diabetic pregnancies.

2. Unraveling the molecular intermediates upstream and downstream of JNK1/2.

After revealing the role of the JNK1/2 pathway, we focused on the upstream JNK1/2 kinase and the downstream transcription factor and responsive gene. We defined apoptosis signal-regulating kinase 1 (ASK1) as the upstream kinase that is responsible for JNK1/2 activation in diabetic embryopathy. Maternal diabetes-induced oxidative stress triggered ASK1 activation. Deleting the Ask1 gene significantly reduced activation of JNK1/2, FoxO3a, caspase activation and neuroepithelial cell apoptosis leading to NTD reduction. Deleting the FoxO3a gene also blocked the pro-apoptotic effect of maternal diabetes and inhibited NTD incidence. We further elucidated that TRADD, an adaptor protein of TNFa cell death receptor pathway, is a target gene of the ASK1-FoxO3a pathway. This data resulted in a high impact factor paper in Science Signaling, which was introduced by the top journal, Cell, in its section of Leading Edge in its September 26, 2013 issue. Our paper was featured in Science, signaling the August 27, 2013 issue’s cover, a podcast and many media outlets, and formulated the basis for US Patent Number: 12/779,935, entitled “Methods of Treating a Diabetic Embryopathy” (Sci Signal 2013; Diabetes 2015; Am J Obstet Gynecol 2010, 2015).

Impact: The studies lay a foundation for targeting the pro-apoptotic kinases, ASK1 and JNK1/2 as therapeutic targets of diabetic embryopathy.

3. Revealing cellular organelle stress as one of the causes of diabetic embryopathy.

My laboratory was the first group in elucidating the role of ER stress and impaired autophagy in diabetic embryopathy. ER stress was induced in neuroepithelial cells of embryos exposed to diabetes, and treatment with the ER stress inhibitor, 4-PBA, reduced high glucose-induced NTDs. We discovered the reciprocal relationship between JNK1/2 and ER stress in diabetic embryopathy. Autophagy is essential for embryonic neurulation. We found that maternal diabetes suppressed autophagy in neuroepithelial cells, and that restoring autophagy by trehalose, a natural disaccharide, resolved cellular homeostatic imbalance by inhibiting ER stress and mitochondrial dysfunction. Seminal studies using the SOD1 Tg mice demonstrated that maternal diabetes-induced nitrosative stress, lipidperoxidation and protein kinase C are linked to cellular organelle stress. These studies led to a US Provisional Patent Application Number: 61/651,189, entitled: “Use of Trehalose for Prevention of Neural Tube Defects” (Am J Obstet Gynecol 2012, 2013; Am J Physiol Endocrinol Metab 2013; Diabetes 2013).

Impact: These discoveries are entirely new and establish the involvement of cellular stress, endoplasmic reticulum stress and autophagy in neural tube defect formation induced by maternal diabetes.

4. Developing natural compounds as prevention for diabetic embryopathy.

My laboratory has developed a number of natural compounds that target maternal diabetes-induced oxidative stress, cellular organelle stress and the pro-apoptotic kinase signaling. Our studies revealed the protective effects of the green tea polyphenol, epigallocatechin-3-gallate, the autophagy activator, trehalose and a turmeric compound, curcumin, against high glucose-induced cellular stress, apoptosis and NTD formation. These findings provide an array of candidate natural compounds with minimal toxicities for the future development of dietary supplements against birth defects in human diabetic pregnancies (Am J Obstet Gynecol 2010, 2015).

Impact: These findings lay the solid foundation for the development of these natural compounds with minimal toxicities for potential dietary intervention in diabetic embryopathy.

5. Elucidating high glucose as a teratogen.

Using the whole-embryo culture system, we have been able to recapitulate maternal diabetes-induced NTDs in an ex vivo preparation. High glucose induces NTD formation by activating JNK1/2 and FoxO3a leading to neuroepithelial cell apoptosis. This ex vivosystem also allowed us to study the impact of high glucose on vasculogenesis and establish the causal relationship between early vasculopathy and late structure anomalies. Maternal diabetes adversely affects neural stem cells in the developing neuroepithelium. Recently, we found that our in vivo findings were recapitulated in a neural stem cell line, C17.2 cell line, which enabled us to study the effect of high glucose on gene regulation. These findings collectively support that high glucose is a teratogen (Am J Obstet Gynecol 2008, 2011, 2015; Toxicological Sciences 2015).

Impact: These studies provide experimental evidence to support the hypothesis that high glucose of diabetes is the cause of diabetic embryopathy and set a foundation for clinical management of euglycemia in diabetic pregnancies.

6. Establishing a type 2 diabetic embryopathy model.

Due to the obesity epidemic, the number of type 2 diabetic women is increasing. We recently established high-fat diet-induced type 2 diabetic embryopathy, which could be inhibited by a type 2 diabetic drug, metformin, whose main function is to reduce blood glucose levels. In this type 2 diabetic embryopathy model, we recapitulated the findings in the type 1 diabetic embryopathy that oxidative stress-induced ER stress and neuroepithelial cell apoptosis are the cause of neural tube defects (Diabetes2015).

Impact: This study developed a suitable model for type 2 diabetic embryopathy model that is not associated with gene mutation and will greatly impact the field in faithfully reflecting type 2 human diabetic pregnancies.

7. Discovering the epigenetic mechanism in diabetic embryopathy.

I was the first investigator to reveal DNA hypermethylation and histone hyperacetylation as the cause of gene dysregulation in diabetic embryopathy (an ADA basic science award). We have linked pro-apoptotic kinase signaling to increased DNA methylation. My group also revealed the critical role of microRNA (miRNA) in maternal diabetes and high glucose-induced neural stem cell apoptosis. To further explore the role of miRNA in diabetes-induced birth defects, I have developed a robust program using miRNA knockout transgenic mice to test the critical involvement of several miRNAs in the etiology of neural tube defects and heart defects (Diabetes 2016 and Toxicological Sciences, 2015).

Impact: These studies bring in the epigenetic concept in the field of diabetic embryopathy.

8. Uncovering the molecular mechanism underlying maternal diabetes-induced heart defects.

The field of maternal diabetes-induced heart defects is a significantly understudied area. Our recent studies revealed ASK1-induced ER stress and cardiomyocyte apoptosis as the cause of heart defects. Maternal diabetes induces oxidative stress in the developing heart leading to gene dysregulation. I have established a robust program in this area with several pending R01 applications and organizing a NIH P01 application (Circ Cardiovasc Genet 2015; Am J Physiol Endocrinol Metab 2015).

Impact: These studies significantly improving our understanding in the etiology of heart defects, the most common birth defects in human and lead to the establish of a robust and highly fundable program in heart defects.

CURRENT PROJECTS

Studying Alzheimer’s Disease with iPSCs

One of our current projects is to try and understand how Alzheimer’s disease affects neurons in the brain. To do this, we will be using modern cell culture techniques as well as state of the art microscope technology to analyze these brain cells. We are turning human fibroblast cells into induced pluripotent stem cells (iPSCs) using human lentivirus sets consisting of Oct4, Sox2, Nanog, and Lin28, and with these iPSCs, we will be reprogramming them into neurons to investigate factors that may potentially induce Alzheimer’s as well as possible treatments for the disease.