Bioengineering a cortical microtissue model to study human microglia in Alzheimer's disease

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PROJECT SUMMARY/ABSTRACT Microglia are highly sensitive to the extrinsic cues from their microenvironment in a context-specific manner and rapidly change around diverse cellular states via intrinsic transcriptional programs. The specific microglial state that contributes to Alzheimer’s Disease (AD) pathology is still illy defined, mostly owing to the longstanding critical need for a reliable and robust modeling tool. In light of the substantial difference between human and mouse microglia, the iPSC-derived human microglia (iMG) have emerged as a rigorous platform to investigate neuroinflammation and AD-linked genetics. A recent transition from 2D to 3D culture systems further enhances the utility of iMG in understanding AD pathogenesis, but technical barriers remain. An improvement to achieve better cellular diversity and functionality in a scalable 3D neural setting will make a desired tool that enables precise monitoring and manipulations of iMG inside a stringently controlled brain-like milieu. Our long-term goal is to understand the pathogenic determinants of neuroinflammation to inform crucial future treatment for AD, via stem cell and engineering innovations. To this end, we propose here to introduce an original 3D culture platform to examine the extrinsic and intrinsic elements of microglial activation in health and in AD, based on patient- derived iMG grown in engineered primary rat cortical microtissues. Leveraging validated AD mutant iPSCs and transgenic AD rats, our overall objectives are to 1) confirm the capability of our hybrid model to recapitulate human-specific, AD-related microglia features and signature and 2) to characterize the ‘ground state’ and neuroinflammatory responses of control and AD iMG under a physiological or pathological microenvironment (i.e. wildtype vs. AD transgenic microtissue). Supported by our preliminary studies, our central hypothesis is that the iMG-microtissue growth system supports maturation and operation of human microglia and can be utilized to detect the nuances in microglial behaviors that may contribute to AD pathogenesis. Our specific aims are to test our working hypotheses that 1) iMG populated in cortical microtissues mimic homeostatic human microglia in vivo and can be phenotyped for microglia-intrinsic manifestations contributed by genotypes, and that 2) iMG maintained in AD mutant microtissues are affected by the AD-promoting extrinsic cues and show disease- associated characteristics. Our expected outcomes are to 1) establish a new-generation in vitro human microglia model system that uniquely allows dissecting the intertwined influences from AD-linked genetics and microenvironment on microglial functions and 2) to acquire a distinctive dataset that would offer a framework to pinpoint critical microglia characteristics for AD. We believe an expansion of this research beyond this award period to characterize in depth the microglial findings uncovered here will ultimately bring a valuable opportunity for the development of much-needed intervention and prevention strategies for AD.