SUMMARY
Pregestational diabetes induces neural tube defects (NTDs). There are 60 million women of reproductive age
(18-44 years old) worldwide, and approximately 3 million American women with diabetes. Even under the best
prenatal care, women with diabetes are still three- to four-times more likely to have a child with birth defects than
women without diabetes. Unraveling the mechanism underlying diabetes-induced NTDs is critical for
understanding its pathogenesis and providing potential intervention targets. Yes-associated protein (Yap), a
transcriptional co-activator, determines body and organ size and regulates cell apoptosis, proliferation, and
differentiation. We found that either conditional KO of Yap or transgenic (Tg) overexpression of constitutively
active Yap (CA-Yap) specifically in the neuroepithelium resulted in NTD formation. Our recently published data
demonstrate that one of the mTOR (mechanistic target of rapamycin) downstream kinase p70S6K1 is activated
by maternal diabetes and its deficiency alleviates diabetic embryopathy. Furthermore, the mTOR inhibitor
rapamycin prevents diabetic embryopathy. Both the HIPPO-Yap pathway and the mTOR pathway induce cell
and tissue growth. Thus, we hypothesize that maternal diabetes activates mTOR-p70S6K1, which
antagonizes Yap by activating the HIPPO kinase Lats1 through phosphorylation, selectively increases
translation and disrupts endoplasmic reticulum (ER) homeostasis, leading to NTDs. Lats1 inactivates
Yap through phosphorylation that disrupts the planar cell polarity (PCP) leading to failed neurulation. To
test our hypothesis, we propose the following aims. Specific Aim 1. determine whether the major mTOR
downstream effector p70S6K1 counteracts Yap activity by phosphorylating Yap upstream kinase Lats1
in diabetic embryopathy. We will examine whether maternal diabetes-activated the mTOR effector p70S6K1,
which forms a tertiary complex with the scaffold protein Merlin and Lats1, triggers Lats1 phosphorylation in two
previously unidentified sites, Thr255 and Thr262, leading to Yap inactivation. Specific Aim 2. To determine
whether the HIPPO signaling kinase Lats1 activation leads to neural tube defects in diabetic
embryopathy. We will test whether maternal diabetes induces Lats1 phosphorylation at new sites and
subsequent the canonical phosphorylation sites which leads to suppression of Yap and NTD formation. Specific
Aim 3. To investigate how fine-tuned Yap activity is critical for neurulation and its dysregulation disrupts
planar cell polarity in diabetic embryopathy. We will assess that Yap activity is tightly controlled during
neurulation and restoring Yap activity can ameliorate diabetic embryopathy. We will further evaluate whether
fine-tuned Yap activity maintains PCP gene expression during neurulation.
