Microglia play an important role in developmental and homeostatic brain function. They profoundly influence the development and progression of neurological disorders, including Alzheimer’s disease (AD). In AD, microglia respond to degenerating neurons, beta-amyloid (Aβ) and tau pathology, and CNS inflammation. AD-etiology involves complex interactions between age, genetic, and environmental risk factors. Recently, GWAS studies in large AD cohorts have identified numerous SNPs present in innate immune genes, many expressed in microglia. These SNPs confer an elevated risk in developing AD, and harboring of these SNPS is considered a risk factor. While the genes themselves are not risk factors, SNPs in these genes may impair the normal function of microglia, such as cytokine production and phagocytosis. Furthermore, many of these genes are involved in the detection or clearance of Aβ, and therefore these SNPs may collectively influence microglia function or influence dysfunction.
Studying human microglia is challenging because of the rarity and difficulty in acquiring cells from human CNS tissue. A methodology for generating human microglia from a renewable source has long remained elusive despite success in generating the other cell-types of the CNS. This elusiveness existed due to the ontogeny of microglia and their unique transcriptome and functional differences versus other myeloid cells. The goal of my dissertation was to generate human induced pluripotent stem cell (iPSC)-derived microglia (iMGLs) to study their molecular and physiological function in neurological disease. To accomplish this goal, I developed a fully-defined protocol to generate large number of pure (>95%) iMGLs under 40 days.
iMGLs are highly like primary human microglia as assessed via whole-transcriptome and functional analyses. iMGL studies, in vitro and in vivo, highly suggest that they can be used as surrogates for human p microglia. Using iMGLs, I showed how AD-GWAS related microglial genes were influenced by two hallmark AD proteins—Aβ and Tau. In addition, I showed that iMGLs populate mouse brains and develop microglial-like arborized morphology and respond to Aβ in an AD transgenic mice. Together, this protocol represents an important advance in our ability to study human microglia in the context of development, health, and disease, such as AD