Examining the Diverse Pathological Consequences of Microglial Absence 

Our understanding of microglia, the principal immune cells of the central nervous system (CNS), continues to evolve as new models and approaches shift our perception of these intriguing cells. Previously envisioned as passive guardians of the brain, microglia have since been shown to play critical roles in development, neuroplasticity, and neurological disease.To further understand the role of microglia in AD and the impact of microglial absence on the aging brain, my thesis studies utilized ‘FIRE mice’, a genetic model that lacks microglia. FIRE mice harbor a homozygous deletion within the Fms intronic regulatory element (FIRE) super-enhancer, leading to a loss of CSF1R expression and congenital absence of microglia.  To examine the role of microglia in AD pathogenesis, I crossed FIRE mice with 5xfAD mice that develop robust beta-amyloid plaque pathology. Remarkably, I found that absence of microglia promotes the development of cerebral amyloid angiopathy (CAA), brain calcification, and cerebral hemorrhages in AD mice. Importantly, transplantation of wildtype microglia prevents each of these pathological changes. To determine whether microglia absence alone can also induce pathological changes within the aging brain, I further examined 9-10 month-old FIRE mice in comparison to wildtype littermates and explored the impact of postnatal microglial transplantation, demonstrating that prolonged absence of microglia leads to the development of astrogliosis, calcification, and seizures, mimicking many of the pathological features of a rare human primary microgliopathy.  Taken together, my thesis studies have revealed important roles for microglia in protecting the brain against age- and disease-related development of vascular, and white matter pathologies. These findings not only deepen our understanding of microglia’s roles in neurodegenerative diseases, but also provide initial evidence to support microglial transplantation as a viable therapeutic approach for a variety of neurodegenerative diseases.

The Blurton-Jones Lab attends ADPD 2024 in Lisbon, Portugal with three talks and two presentations. Congratulations to our speakers and graduate student, Alina Lahian, on her poster presentation!

Engineering human induced pluripotent stem cells to enable microglial replacement therapy in the central nervous system

Immune cell therapies (ICT) are becoming more mature options for a  variety of diseases. As the resident immune cell of the brain, microglia stand out as the ideal candidate for ICT approaches in the central nervous system. Combining recent advances in gene editing and iPSC-microglia (iMG) differentiation, we sought to investigate whether microglia could be harnessed to provide widespread delivery of therapeutic cells and proteins to the brain. Collectively our studies have revealed three principal findings: 1) iPSC-microglia can be widely engrafted into a recipient adult brain via an inhibitor-resistant protocol; 2) transplantation of CRISPR-corrected iPSC-microglia can prevent and even reverse neuropathologies in a mouse model of ALSP, a rare neurodegenerative disease caused by loss of microglia; and 3) iPSC-microglia can be genetically-engineered ex vivo to effectively deliver therapeutic proteins locally or CNS-wide in response to neuropathologies such as amyloid plaques. Together these findings suggest that patient-derived microglia could offer a promising new platform for the development of future immune cell therapies in the CNS.

CRISPR generation of CSF1R-G795A human microglia for robust microglia replacement in a chimeric mouse model

Chimeric mouse models have recently been developed to study human microglia in vivo. However, the widespread engraftment of donor microglia within the adult brain has been challenging. Here, we present a protocol to introduce the G795A point mutation using CRISPR-Cas9 into the CSF1R locus of human pluripotent stem cells. We also describe an optimized microglial differentiation technique for transplantation into newborn or adult recipients. We then detail pharmacological paradigms to achieve widespread and near-complete engraftment of human microglia. For complete details on the use and execution of this protocol, please refer to Chadarevian et al. (2023).

Healthy, Drug-Resistant Microglia Reinvigorate Mouse Brain

06 Jan 2023

Rather than fixing dysfunctional microglia, why not replace them with shiny new cells? In a collaborative effort to inch microglia transplant closer to reality, researchers led by Chris Bennett, University of Pennsylvania, Philadelphia, and Mathew Blurton-Jones, University of California, Irvine, created mouse macrophages and human microglia, respectively, that resist colony-stimulating factor 1 receptor inhibitors. CSF1R activity is essential for macrophage and microglial viability. In the December 30 Journal of Experimental Medicine, they reported that these mutant cells repopulated 75 to 99 percent of mouse brains cleared of native microglia. The inhibitor-resistant cells retained normal gene expression and function.

Researchers applauded the work. “This study sets the new gold standard for studies of microglial replacement, enabling human-relevant studies of microglia biology,” wrote Diego Gomez-Nicola, University of Southampton, U.K. David Gate of Northwestern University in Evanston, Illinois, called this a landmark study. “It has clinical implications for treating neurodegenerative disease, lysosomal storage disorders, and other brain abnormalities,” he wrote.

For the full article, click here.

Congratulations to Dr. Jaclyn Beck on her successful PhD dissertation defense “Innate and Adaptive Immunity in Aging and Alzheimer’s Disease.”