Mammalian cortical development is a complex and tightly regulated process. While it is known that humoral and transcriptional regulation generates the cellular diversity in the mammalian telencephalon, a relatively unexplored area is whether the progenitor populations are also metabolically distinct and the extent to which metabolic regulation of precursor cells contribute to neurogenesis in the telencephalon. AMP- activated protein kinase (AMPK) is an energy sensor and plays a central role in energy and redox homeostasis in all eukaryotic cells. Recent studies show, that AMPK controls many fundamental processes including regulation of cell structures, polarity, cell division, migration and normal growth and development of organisms. In this application we will test our hypothesis that AMPK regulates neurogenesis in the telencephalon though its energy sensing functions. AMPK exists as a heterotrimer of catalytic ? and regulatory ? and ? subunits. Mammals express 2?, 2? and 3? subunits. Not much is known about AMPK function in neural cells. Studies in Drosophila demonstrate that AMPK is necessary for maintaining mitotic competence of neural precursors and loss of AMPK function also causes progressive neurodegeneration. Our published study (Dev. Cell, 2009) in the germline ?1 mutant mice shows massive apoptosis, which was primarily restricted to the intermediate progenitors (IPCs and their progeny) of developing telencephalon in the prenatal embryo, while in the postnatal brain apoptosis was restricted to the external granule layer of the developing cerebellum. In vitro analysis showed cell-intrinsic G2M-specific defects and apoptosis of ?1 mutant neural precursors. In this application, we will focus on the telencephalon. With the help of our recently generated ?1 conditional knockout mouse and other transgenic mice, we will conduct bioenergetics studies to examine whether metabolic uniqueness of dorsal and ventral telencephalon IPCs render them more sensitive to loss of AMPK function during their proliferation, survival, migration and differentiation (Aim1). We will examine regional control of neurogenesis by ?1 in the dorsal and ventral telencephalon in vivo, by using region-specific Cre lines to reduce ?1 function (Aim2).
In Aim3, we will use three cutting edge technologies to investigate region-specific tissue bioenergetics and metabolomics in the intact brain in vivo. We expect that our studies will provide new dimensions to our understanding of cortical development in the light of cellular metabolism. Identification of novel AMPK effectors and AMPK subunit-specific small molecule modulators could one day potentially lead to novel therapeutics for neurodegenerative and metabolic diseases.
AMPK is an important mediator of glucose sensing and nutrient metabolism in the CNS. Inappropriate AMPK activation in the brain causes deleterious effects. Because the rapidly developing brain is vulnerable to nutrient deficiency or overabundance, gestational diabetes or malnutrition (that cause birth defects and memory deficits), is likely to trigger improper AMPK activation in the fetus. This could lead to cortical malformations and developmental defects in the fetal brain and cognitive deficits in children. Thus, AMPK modulating drugs could have a direct effect on fetal corticogenesis. In fact, one mechanism by which the widely prescribed drug metformin works in Type2 diabetes is by its action on AMPK. Little is known however, whether metformin has any direct effect on AMPK activation in the fetal brain. Understanding the subunit-specific functions of AMPK would lead to interest in developing AMPK heterotrimer-specific AMPK modulators. Moreover, our preliminary studies in the AMPK?1 mutant mouse show preferential loss of IPCs that give rise to interneurons. Understanding the mechanisms that regulate interneuron generation and migration is important as the complexity of the primate brain is attributed to the massive proliferation of these progenitors and defective interneuron development and migration is correlated with various neurological disorders like schizophrenia, epilepsy and lissencephaly. Our studies will open exciting new avenues of research in identification of novel AMPK subunit-specific small molecule modulators which could potentially lead to novel therapeutics for neurodegenerative and metabolic diseases.
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