Sam & Geri Rashid Developmental Neurobiology Laboratory
The current focus of the laboratory is to investigate novel treatments for Alzheimer's disease and abnormal brain development and its related mental disorders including autism. These studies include: 1) identifying several natural compounds which can be effective treatments for Alzheimer’s disease by promoting nonamyloidogenic processing of amyloid precursor protein (APP) in cellular and animal models. 2) Analyzing the role of the immune system in modulating amyloid/tau pathology in experimental animal models of Alzheimer’s disease following administration of natural compounds as well as human umbilical cord blood cells. 3) Elucidating the role of molecular mechanisms in the creation of neurons and their growth in the developing fetus.
Immunotherapy for Alzheimer’s disease
Our early research focuses on the role of CD40-CD40 ligand (CD40L) interaction in the development of Aβ/β-amyloid pathology in mouse models of Alzheimer’s disease (AD). We were first to characterize an immune molecule on the surface of nerve cells, or neurons, called CD40. With a team of collaborators, we discovered that CD40-CD40L interaction plays a critical role in Aβ-induced microglial activation. Following these findings, we further investigated the role of p44/42 mitogen-activated protein kinase (MAPK) in CD40-mediated signaling in cultured microglial cells and the role of stimulation of CD45, a membrane-bound protein-tyrosine phosphatase (PTP), in negative regulation of this pathway. These early works first provide a genetic engineering approach to identify therapeutic targets for the treatment of AD. Based on these findings, we developed a patent entitled “Assay for evaluating the therapeutic effectiveness of agents in reducing Alzheimer’s disease pathology”. It has been issued with US200050089939. In addition to the contributions described above, we are also interested in developing the novel treatments for AD and other neurodegenerative disorders. For this purpose, our laboratory has first established the transdermal Aβ vaccines for AD in mouse models of the disease. This work was covered by various news media including BBC and the Washington Post.
Our recent works first characterized the capacity of certain Aβ autoantibodies in driving or opposing Aβ generation at the level of amyloid precursor (APP) processing, which could be of etiological importance in the development of sporadic forms of AD. Furthermore, these studies are also very informative for the future passive or active anti-Aβ immunotherapies. That is, we originally discovered potential off-target effects resulting from antibodies targeting the N-terminus of Aβ, as co-binding to the corresponding region of APP may actually enhance or inhibit Aβ generation. Finally, the results from this study primarily provide us with foundational knowledge to develop an Aβ autoantibody functional assay to diagnose AD at earlier stages. Our most recent works have focused on exploring the role of aging immunity in the development of sporadic forms of AD in mouse models.
Drug discovery for Alzheimer’s disease
We were the first to show that EGCG, the main naturally-occurring polyphenolic constituent of green tea, reduces Aβ generation in “Swedish” mutant APP-overexpressing primary neurons and neuron-like cells. In concert with these observations, we found that EGCG promotes cleavage of α-CTF and elevates sAPPα. These cleavage events are associated with elevated α-secretase cleavage activity and enhanced activation of a-disintegrin-and-metalloprotease 10 (ADAM10), a primary candidate α-secretase. As a validation of these findings in vivo, we treated Aβ-overproducing Tg2576 transgenic mice with EGCG and found decreased Aβ levels/plaques in the brain associated with promotion of the non-amyloidogenic-secretase proteolytic pathway. Furthermore, this treatment also provided cognitive benefit to Tg2576 mice, specifically resulting in improved working memory. Furthermore, we found that EGCG functions through estrogen receptor-mediated activation of ADAM10 in the promotion of non-amyloidogenic processing of APP. Most recently, we have shown that inadequate sAPPα levels may be sufficient to polarize APP processing toward the amyloidogenic, Aβ producing route. Thus, restoration of sAPPα or mitigation of its association with β-secretase (BACE) may be a viable therapeutic strategy to prevent abnormalities in APP processing that lead to AD pathogenesis. In addition to the contributions described above, we have recently found that luteolin, a naturally occurring flavonoid, inhibits β-amyloid production through inhibition of GSK3α-mediated presenilin dephosphorylation.
Most recently, our group has employed crystal engineering techniques to create novel ionic cocrystals (ICCs) of lithium therapeutics. Recently, we were the first to report the crystal structure of an ICC of lithium with an organic anion, salicylic acid, and l-proline (LISPRO). We also were the first to show that this change in speciation did not negatively affect the bioactivity of lithium at several endpoints with relevance to the treatment of neurodegenerative diseases like AD. These clinically relevant endpoints included: increasing inhibitory GSK3β (Ser9) phosphorylation and decreasing tau hyperphosphorylation in human tau transfected HeLa cells, modulating/rebalancing GSK3β (Ser9/Thr390) phosphorylation, decreasing levels of tau hyperphosphorylation, and reducing β-amyloid pathology in Tg2576 mice. In addition, LISPRO treatment promotes anti-inflammatory/Th2 responses and decreases proinflammatory soluble CD40 ligand (CD40L) in the CNS of these mice. This in vivo effect of LISPRO on rebalancing anti-/pro-inflammatory responses was further supported by the in vitro effect of LISPRO in reducing microglial activation-induced by IFNγ and CD40 signaling and enhancing the aged Aβ peptide phagocytosis in primary microglial culture cells. This work builds on our recent successful use of cocrystal technology to vastly improve the oral bioavailability of bioflavonoids, quercetin and EGCG. Currently, we intend to fully characterize LISPRO’s therapeutic potential in 3XTg-AD mouse model. This work will lay the foundation for possible future clinical translation which adds a safe lithium option for reduction of AD pathology and symptoms.
Autism & other brain development associated mental disorders
Lastly, we have brought our expertise in immunity and inflammation in the adult brain to bear on disorders of brain development affecting children. Recently, we found a significantly increased level of sAPPα in 60% of the known autistic children. Based on this study, we have recently developed transgenic mice which overexpress this pro-brain growth protein (human sAPPα) in the central nervous system (CNS). We have investigated the effects of over-production of human sAPPα on abnormal brain growth and immune homeostasis in these mice. Our studies demonstrate (1) overexpressing sAPPα could be a probale biomarker in the early diagnosis of autism; (2) that overproduction of sAPPα also plays a key role in producing autism-like pathology as well as autistic behavioralchanges in the mice.