Author ORCID Identifier

https://orcid.org/0000-0001-6293-4827

Semester

Spring

Date of Graduation

2025

Document Type

Dissertation

Degree Type

PhD

College

School of Medicine

Department

Microbiology, Immunology, and Cell Biology

Committee Chair

Karen Martin

Committee Co-Chair

Candice Brown

Committee Member

Candice Brown

Committee Member

Jennifer Franko

Committee Member

Courtney DeVries

Committee Member

Matthew Dietz

Abstract

Abstract

Therapeutic Roles for Alkaline Phosphatases to Target Intestinal Dysfunction in Mouse Models of Experimental Sepsis and Ischemic Stroke

Rhiannon V. Macom

Stroke is a disease that primarily affects the brain; however, ongoing research continues to show that stroke has far reaching systemic effects that can affect both short- and long-term recovery. The gastrointestinal tract has been shown to be affected post-stroke, and these effects are likely due to the bidirectional communication between the gut and the brain via the gut-brain-axis. Alkaline phosphatases (APs) are common membrane bound enzymes that are known to have a role in mitigating inflammation. The objective of this dissertation was to examine the potential impacts of utilizing a recombinant alkaline phosphate drug known as recAP in sepsis and stroke outcomes. Our central hypothesis was that treatment with recAP would lead to improved outcomes within the brain and the gut. We first optimized a model of recAP administration in sepsis and showed that recAP did affect gastrointestinal outcomes and led to improved post-sepsis outcomes. Since intestinal alkaline phosphatase, encoded by the Akp3 gene, is localized in the intestine, we then interrogated the role of this AP in the gut-brain axis during ischemic stroke. We assessed a novel protective role for recAP in a photothrombotic stroke model by utilizing Akp3-/- and Akp3+/+ mice. This study demonstrated that at 72 hours post-stroke, recAP treatment in the Akp3+/+ mice led to a decrease in infarct size and neurological scoring, alteration of bacterial burden and short chain fatty acid composition, and improved crypt: villi ratios in the ileum. We also found that, when compared to Akp3+/+ mice, Akp3-/- mice had smaller infarcts, a longer crypt: villi ratio in the ileum, alterations in the brain immune cell populations, altered fecal short chain fatty acid composition, and increased small intestinal adhesion molecule expression. Results from this study highlighted the potential for recAP treatment post-stroke as well as the need to further investigate the role of intestinal alkaline phosphatase’s mechanisms post-stroke. In our final study, we assessed the effects of recAP on the gut-brain axis in C57Bl/6J mice following a seven-day ischemic stroke. Although we did not observe any neurological deficits, we did identify important shifts in the microbiome as well as in the gene expression of the small intestine, these findings provide further support that recAP may have an important role in modulating the gastrointestinal response post-stroke. In summary, this body of work demonstrates that: 1) Loss of intestinal alkaline phosphatase leads to beneficial post-stroke outcomes in acute stroke and 2) Treatment with recAP post-stroke is likely beneficial; however, the benefits are likely dependent on the mouse strain as well as time post-stroke. We conclude recAP administration and/or modulation of intestinal alkaline phosphatase may be a promising stroke therapeutic to ameliorate the systemic effects of stroke on in conjunction with other FDA-approved therapeutics to improve overall stroke outcomes and quality of life in stroke survivors.

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