Here is another abstract, because I have to write two abstracts for my
qualifying exam.
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Not only are neural stem cells important in learning and memory, they are
also potential therapeutic approaches for neurodegenerative and other neural
pathological diseases. Adult neurogenesis occurs in the subventricular zone
(SVZ) of the lateral ventricle and subgranular zone (SGZ) in the
hippocampus (Suh et al., 2009). Relatively little is known about the
metabolic control of stem cells. Recently, Lkb1, a gene regulating
metabolism has also been shown to regulate hematopoietic stem cells
proliferation (Nakada et al., 2010). More recently, it has also been shown
that genes regulating de novo lipogenesis regulate the proliferation of
neural stem and progenitor cells (NSPCs) (Knobloch et al., 2013). However,
whether it’s the de novo generated lipids or other functions of the genes
that regulate the proliferation of NSPCs is not clear, nor is the detailed
mechanism. Therefore, in this grant, we aim to address these questions.
Aim 1. Whether it's the complex fatty acids that fuel the proliferation of
NSPCs. There are many potential ways through which fatty acids can regulate
the proliferation of NSPCs. However, the possibility that it's some other
functions besides lipogenesis of Spot14 that promotes the proliferation of
NSPCs also exists. To shed some light into the underlying mechanism, we will
feed Fasnflox/flox and Spot14flox/flox mice with a high-fat diet (known to
suppress de novo lipogenesis gene expression) after a series of tamoxifen
injection.
Sub aim 1.1 Because the membrane is composed of a relatively constant ratio
of aliphatic fatty acids over cholesterol (Nohturfft et al., 2009), if it’s
solely membrane biogenesis that can promote the proliferation of NSPCs,
there should be concomitant up-regulation of cholesterol synthesis
accompanying fatty acid synthesis. We will test this by examining the
expression level of cholesterol synthesis genes such as HMGCR (HMG CoA
reductase). We will also overexpress/knock down these genes to see if that
can phenocopy/reduce the proliferation of Spot14 over-expressing cells,
respectively.
Sub aim 1.2 Nuclear receptor PPAR gamma has been shown to promote
neurogenesis. The ligands for PPAR gamma such as linoleic acid can be
generated endogenously from fatty acids. The fatty acids thus produced could
be functioning through the PPAR gamma pathway. To test this hypothesis, we
will be utilizing PPAR gamma agonists/antagonists to see if that could
phenocopy/prevent the proliferation of Spot14 over-expressing cells. In
addition to that, we will use PPAR gamma knockout cells, or siRNA, to look
at loss of function.
Aim2, How NSPCs transition from low-proliferating state to high-
proliferating state, i.e., how low-proliferating cells turn down Spot14
expression and switch to high-proliferating state and how this transition is
responding to extracellular signals is not clear. SREBP-1c has been shown
to regulate Spot14 expression at the transcriptional level (Mater et al.,
1999). A series of growth factors influence the expression of SREBP-1c,
among which is VEGF (Nohturfft et al., 2009). Considering the vascular niche
of neurogenesis (Suh et al., 2009), this is an especially attempting
candidate. Therefore, we will test whether VEGF can influence the
proliferation of NSPCs through regulating SREBP-1c and Spot14 expression. We
will first establish the link between SREBP-1c and Spot14 in NSPCs by over-
expressing SREBP-1c. We will then establish the link between VEGF and SREBP-
1c by treating NSPCs with VEGF.
