Circadian Perturbations of the Vasculome and Microgliome in Alzheimer’s Disease

2022, 2025

The Lo laboratory investigates the molecular mechanisms underlying cell death and network dysfunction following stroke and other forms of neurovascular trauma. Dr. Lo’s interest in Alzheimer’s disease began after conversations with RLG Chair Rudy Tanzi, who noted that up to two-thirds of Alzheimer’s patients also have vascular comorbidities such as hypertension or cerebrovascular disease. At the time, little was known about how Alzheimer’s disease affects the brain’s blood vessels at the genetic and molecular levels. With support from their first CureAlz- funded grant, the Lo lab set out to map gene expression changes in the brain vasculature of two amyloid mouse models. They found that many genes were altered in these mice, and some of these changes could be partially reversed through exercise. Since exercise is a well-established modifiable risk factor for dementia, these findings suggest that its protective effects may come, at least in part, from the ability of exercise to rescue vascular function in the Alzheimer’s brain. 

The origins of the Lo lab’s current project lie in a serendipitous mistake that occurred during their first study. As part of their ongoing stroke research, the lab was investigating how circadian timing affects the efficacy of stroke treatment. Stroke research in mouse models is typically performed during the daytime. However, mice are nocturnal. So, this means that almost all scientific knowledge about mechanisms and therapeutic targets in stroke is limited to sleep-phase strokes. In contrast, the majority of strokes in humans occur during daytime hours, and most patients enrolled in clinical trials have experienced daytime strokes. To address this circadian mismatch—where humans typically have strokes during their active daytime hours while nocturnal mice are naturally sleeping during the day—the Lo lab housed mice in reverse light cycle rooms (lights off during the day and on during the night). This ensured that when lab experiments were performed during normal daytime hours, the mice would be in their active, awake phase. 

By accident, some of the mice used for the CureAlz-funded Alzheimer’s experiments were housed in this reverse light cycle room, while others remained on a normal light/dark schedule. As a result, the lab collected data from mice operating on opposite circadian schedules—one during their active (wake) phase and the other during their rest (sleep) phase. Surprisingly, the circadian stage during which the data was collected had a profound impact on gene expression in the neurovasculature (known as the vasculome) between control mice and those that modeled Alzheimer’s. This unexpected discovery pointed to a previously unrecognized role for circadian rhythms in vascular gene regulation in Alzheimer’s disease. 

Based on these findings, Dr. Lo hypothesizes that amyloid pathology disrupts the brain’s vasculome and several aspects of microglial biology (the microgliome) across brain regions, which in turn disrupts circadian rhythms. This disruption may create a harmful feedback loop that further exacerbates amyloid buildup and inflammation and worsens gene pathways involved in AD pathogenesis. To test this, the Lo lab is mapping the circadian and diurnal gene expression patterns of the vasculome and microgliome in amyloid mice raised in either light-dark or constant-dark conditions. In response to reviewer feedback, they are also collecting pilot data from aged control mice exposed to repeated circadian disruption to isolate the effects of disrupted rhythms alone. Finally, they are testing whether exercise during the mice’s active phase can help restore circadian rhythms and normalize vascular and immune gene expression in the Alzheimer’s brain. 

Dr. Lo’s work will generate important data for the Alzheimer’s field, even if his intervention—exercise—does not restore circadian rhythms because the lab is collecting an important new dataset. Most biomedical research mouse studies take place during the workday, when humans are active, but mice are naturally resting. Dr. Lo demonstrated significant differences in gene expression tied to different points of the circadian cycle. By testing mice during their naturally active phase, Dr. Lo’s experiments will interrogate a more realistic and thus translational scenario. 

Dr. Lo’s team made good progress during their first funding period. In aged control mice, they established a baseline by identifying gene sets in the brain’s vasculome and microgliome that follow circadian rhythms. These findings, mapped in both the cortex and corpus callosum, provide a reference point for comparing changes in Alzheimer’s disease models. They also identified several key genes that lost circadian rhythmicity with age in important brain regions. In an amyloid (5xFAD) mouse model, the team mapped gene expression changes during both the light and dark phases. The light phase was associated with increases in genes involved in angiogenesis and vascular development, while the dark phase showed increases in genes related to dendritic spine and body fluid level maintenance, as well as tissue remodeling. Across both phases, they observed an increase in microglial activation and phagocytosis genes, suggesting a microglial-mediated response to Alzheimer’s pathology regardless of phase. Furthermore, the 5xFAD mice also showed disrupted expression of circadian rhythm genes in the vasculature, particularly during the dark phase, which corresponds to the mice’s natural period of activity. This finding could have broad implications for Alzheimer’s research, as the vast majority of mouse studies are performed during the day when mice are typically at rest. As a result, many experiments may be missing key gene expression differences tied to circadian timing. 

In the second funding period, Dr. Lo’s team will perform experiments investigating the potential role of exercise in resetting the disrupted circadian rhythms of the 5xFAD mice. Dr. Lo also plans to conduct more in-depth analyses of the single-cell RNA sequencing datasets they have already collected to identify cell heterogeneities across gray and white matter regions. In addition, exploratory studies will also be conducted to ask whether drugs that modulate circadian genes can be used to rescue vascular and immune dysfunction in the 5xFAD mice. Altogether, these studies may not only change the way we study Alzheimer’s model mice but also provide novel insights into how circadian biology regulates vascular and immune responses in Alzheimer’s disease. 

 


Funding to Date

$400,833

Focus

Studies of Alternative Neurodegenerative Pathways, Translational

Researchers

Eng H. Lo, Ph.D.