Niccolo Terrando - US grants

This R21 application uses the high risk, high reward technique of mass cytometry (abbreviated as CyTOF) to identify immune cell subsets that mediate neuroinflammation in the central nervous system (CNS) in a well- established orthopedic mouse model of postoperative delirium (POD). Dysregulated immunity is a hallmark of normal aging; it is also recognized as a key feature of many neurological disorders including dementia and perioperative complications like delirium. POD is common, occurring in up to 50% of older patients after a fracture repair. The strongest risk factors for POD are advanced age and dementia. Interestingly, the postoperative emergence of delirium may presage dementia. In fact, delirium superimposed on dementia (DSD) contributes to a faster trajectory of cognitive decline as well as significant mortality. This is significant because of the millions of elderly patients that routinely undergo orthopedic or other surgeries every year. The biologic mechanisms that drive POD and DSD during aging are unknown and without approved drugs to treat or prevent it. We have pioneered a clinically-relevant orthopedic surgery murine model that displays systemic inflammation, alters microglial activation, and causes memory deficits in mice. In our model, surgery mobilizes discrete immune cell populations with pro-inflammatory signaling responses that mediate damage to the blood-brain barrier, damage the neurovascular unit (NVU) and impair normal synaptic transduction. Translationally, similar immune signatures with the same pro-inflammatory markers have now been described in fluid biomarkers of delirious patients. However, current immunophenotyping is limited to selected non-specific cytokines and pro- inflammatory molecules such as TNF, IL-1, IL-6, MCP-1 and S100b in brain tissue (rodents) and cerebrospinal fluid (humans). No study has yet attempted to unbiasedly profile the immune subset specific response to orthopedic surgical trauma in the CNS. We propose two specific aims: (1) to define how age differences between young adult (6mos) and elderly (22mos) male and female mice modulate immune cell subsets in the CNS and blood after orthopedic surgery; and (2) to determine the impact of Alzheimer?s (AD)-like pathologic features using 5xFAD transgenic male and female mice at 6mos of age (when AD and postoperative neuroinflammation become pathologically significant) on immune cell subsets in the CNS and blood after orthopedic surgery. The ability to resolve immune cell subsets and align them with discrete repertoires of pro-inflammatory signaling molecules with CyTOF will be key to understanding whether POD results from neuroinflammation due to peripherally migrating and/or CNS-resident immunocytes. These experiments will provide the foundation for future RO1 studies in which we pursue key findings focused on dysfunction of the NVU associated with neurodegeneration in Alzheimer?s disease as sought by NOT-AG-19-033. We expect our findings to have an important positive impact on the ADRD field to reduce the impact of delirium and dementia in the aging population by helping identify patients at greater risk for developing POD and DSD.

ABSTRACT Impaired cognitive function after common surgical procedures is a growing concern especially among over 5 million people in the United States who suffer from dementia, including Alzheimer's disease (AD), and thus have a 3-fold increased risk for fracture requiring surgical repair. After orthopedic surgery, acute changes in cognitive function, often referred to as postoperative delirium, occur in up to 89% of patients with preexisting dementia, and associate with poorer prognosis and even 2-fold greater risk for 1-year mortality compared to patients without dementia or delirium. Our long-term goal is to define the mechanisms that underlie surgery- induced cognitive dysfunction, and to provide safe and effective approaches to reduce this potentially devastating complication. In the proposed study, we will model postoperative delirium superimposed on dementia by subjecting mice with cerebral amyloid angiopathy (CAA), which is common in AD patients, to orthopedic surgery (tibial fracture). Our overall objective is to determine the role of the blood?brain interface (the neurovascular unit (NVU) and the blood-brain barrier (BBB) within) and vascular ?-amyloid deposition in cognitive function after orthopedic surgery in CAA mice. The central hypothesis is that surgery-induced BBB/NVU dysfunction is worsened in the presence of CAA, and that this is potentially preventable by regulating microglial function, which in turn, can impact postoperative cognitive outcomes. This hypothesis is based on preliminary data acquired in the applicants' laboratories, and will be tested by pursuing 3 specific aims: 1) Analyze BBB/NVU dysfunction in a CAA mouse model after orthopedic surgery; 2) Define the extent to which systemic inflammation and monocyte infiltration impact microglial function in CAA mice after orthopedic surgery; and 3) Determine the effects of an MLK3 inhibitor on microglial function, vascular ?- amyloid deposition, and cognition in CAA mice after orthopedic surgery. Feasibility for these models and techniques has been established in the applicants' hands. In this innovative approach, real-time in-vivo brain imaging and postmortem analyses will be combined with unbiased profiling of the neurovasculature and novel behavioral assays to define delirium-like changes in dementia-prone mice. The rationale for the proposed research is that successful completion will advance and expand our understanding of how surgery affects the blood-brain interface, and will provide new molecular mechanisms of relevance to delirium, neurodegeneration, and aging. Such knowledge is highly significant because it has the potential to improve surgical outcome and quality of life for millions of elderly vulnerable patients in the United States.