(2et) Driving and Suppressing Clonal Expansion in Engineered Stem Cell Environments

Aging of the hematopoietic bone marrow microenvironment produces extrinsic and intrinsic pressures that select for survival and expansion of specific hemopoietic stem cell (HSCs) subtypes. This process, termed clonal expansion, is concurrent with metabolic dysregulation that is the hallmark of an aged stem cell, resulting in loss of HSC diversity and regenerative potential, and a vulnerable immune system. Identification of extrinsic factors to drive or suppress clonal expansion and metabolic dysregulation will provide a route to understanding aging and development of therapeutic routes to target malignancies (leukemia, anemia). However, mechanistic insight into in vivo pressures that drive clonal hematopoiesis is hindered by coupling of cellular, soluble, and matrix cues. Alternatively, in vitro tissue engineering approaches enable independent presentation of extrinsic cues (soluble factors, oxidative stress, matrix properties), to identify features that support metabolic dysregulation and drive clonal expansion. By combining tissue engineering approaches with interrogation of metabolic pathways, causal links between extrinsic and intrinsic selective pressures can be leveraged to suppress clonal expansion and aging of the stem cell population. Thus, my research program will initially identify extrinsic cues that support metabolic dysregulation and aging of the hematopoietic system.

• Role of microenvironment in clonal hematopoiesis
• Metabolic drivers of aged hematopoiesis
• Protection from aging in a diverse population

Stiffness-induced metabolic dysregulation drives fatty liver progression. Department of Materials Science & Eng., Stanford University (Advisor: Sarah C. Heilshorn)

My postdoctoral research identifies metabolic dysregulation induced by the altered extracellular matrix of the diseased liver. Current research into development of fatty liver is limited by animal models that do not accurately capture progression of liver disease. To overcome this challenge, I have developed an in vitro model of liver disease using a chemically-defined, recombinant liver-mimetic tissue microenvironment that permits formation of human, induced pluripotent stem cell (iPSC) derived hepatic (liver) organoids. Using small molecules, I have on-demand control of material properties of the culture platform, mimicking the hardening of the diseased liver. By incorporating diet-related fatty acids, I have demonstrated the development of a fatty liver phenotype and identified a putative mechanistic link between mechanosignaling pathways and fatty acid uptake. Using lipidomics, the large-scale study of lipids and their metabolites, I seek to identify altered metabolic profiles of hepatic organoids that lead to cytotoxic events that further drive progression of fatty liver. By identifying extrinsic predictors (stiffness) that lead to an intrinsic response (metabolic), my work will produce fundamental insight into how the surrounding environment drives disease progression.

Development of an artificial hematopoietic stem cell niche. Department of Materials Science & Eng., University of Illinois Urbana-Champaign (Advisor: Brendan A.C. Harley)

My dissertation research identified essential features of an artificial hematopoietic stem cell niche required to maintain the HSC population in vitro. HSC transplants are a vital therapeutic tool for treatment of blood and immune disorders. However, the rarity of the HSC population (<0.1% of the human bone marrow) limits the efficacy of transplants. Current methods of expansion lead to exhaustion of the stem cell population and limited regenerative potential. To overcome this challenge, I used materials design and proteomics to identify cell-cell interactions that led to maintenance of a stem cell population. Using a library of gelatin-based matrices, with distinct material properties, I engineered a culture platform that directed cell-cell communication by restricting or promoting diffusion of cell-secreted soluble factors. Using a co-culture of mesenchymal stromal cells (MSCs) and HSCs, I characterized material property regimes in which HSCs experienced predominantly autocrine vs paracrine signaling. Using statistical modeling techniques to connect soluble factors with HSC phenotype, I identified specific MSC-secreted factors that led to increased HSC maintenance. Overall, my research used materials design, proteomics, and statistical modeling to identify features of an artificial niche that are essential for maintenance of a hematopoietic population.

Selected Publications:

• LeSavage, B.L., Gilchrist, A.E., Krajina, B.A., Karlsson, K., Smith, A.R., Karagyozova, K., Klett, K.C., Curtis, C., Kuo, C.J., Heilshorn, S.C., Engineered extracellular matrices reveal stiffness-mediated chemoresistance in human pancreatic cancer organoids. In revision, Nature Materials
• Pastrana-Otero, I., Majumdar, S., Gilchrist, A.E., Harley, B.A.C., Kraft, M.L. Identification of the differentiation stages of living cells from the six most immature murine hematopoietic cell populations by multivariate analysis of single-cell Raman. In revision, Analytical Chemistry
• Gilchrist, A.E., Harley, B. A. C., Engineered tissue models to replicate dynamic interactions within the hematopoietic stem cell niche. Advanced Healthcare Materials. 2022, 11, 7:2102130. 1002/adhm.202102130
• Gilchrist, A.E., Serrano, J.F., Ngo, M.T., Hrnjak, Z., Kim, S., Harley, B.A.C., Encapsulation of murine hematopoietic stem and progenitor cells in a thiol-crosslinked maleimide-functionalized gelatin hydrogel. Acta Biomaterialia. 2021, 131, 1, 138. PMC8373770
• Gilchrist, A.E., Harley, B.A., Connecting secretome to hematopoietic stem cell phenotype shifts in an engineered bone marrow niche. Integrative Biology. 2020, 7, 12:175. PMC7384206
• Richbourg, N.R., Wancura, M., Gilchrist, A.E., Toubbeh, S., Harley, B.A.C., Cosgriff-Hernandez, E., Peppas, N.A., Precise control of synthetic hydrogel network structure via linear, independent synthesis-swelling relationships. Science Advances. 2021, 7, 7:eabe3245. PMC7880590
• Ngo, M.T., Barnhouse, V.R., Gilchrist, A.E., Mahadik, B.P., Hunter, C.J., Hensold, J.N., Petrikas, N., Harley, B.A.C., Hydrogels Containing Gradients in Vascular Density Reveal Dose-Dependent Role of Angiocrine Cues on Stem Cell Behavior. Advanced Functional Materials. 2021. 31, 2101541. 10.1002/adfm.202101541
• Pastrana-Otero, I., Majumdar, S., Gilchrist, A.E., Gorman, B. L., Harley, B. A. C., Kraft, M. L., Development of an inexpensive Raman-compatible substrate for the construction of a microarray screening platform. Analyst. 2020, 145, 21:7030. PMC7594104
• Gilchrist, A.E., Lee, S. Hu, Y., Harley, B.A., Soluble signals and remodeling in a synthetic gelatin-based hematopoietic stem cell niche. Advanced Healthcare Materials. 2019, 8, 1900751. PMC6813872

Selected Awards:

• Ruth L. Kirschstein F31 Predoctoral Fellowship, F31-DK117514 (NIDDK)
• T32 Tissue Microenvironment Training Program Scholar, T32-EB019944 (NIBIB)
• Teachers Ranked as Excellent, University of Illinois Urbana-Champaign
• Mavis Future Faculty Fellowship, University of Illinois Urbana-Champaign
• Outstanding Poster Award, Gordon Research Conference, Signal Transduction by Engineered Extracellular Matrices
• Racheff Teaching Fellowship, University of Illinois Urbana-Champaign
• Donald W. Hamer Fellowship, University of Illinois Urbana-Champaign

Teaching Interests:

My academic and research education in chemical engineering, materials science, and tissue engineering has exposed me to a broad, interdisciplinary range of subject matters. Based upon my undergraduate education in chemical engineering, dissertation work in cell-cell interactions, and my postdoctoral work in materials chemistry, I am qualified to teach core chemical engineering subjects related to fluid mechanics, transport phenomena, kinetics and reactions, and thermodynamics. Additionally, based upon my teaching experience, I enjoy and am qualified to teach subjects that introduce topics in biomaterials, tissue and cellular engineering, and polymers. I have found that students are particularly engaged during introductory classes and use such classes to inform their future interests, presenting a unique opportunity to engage with students and shape their academic career.

Teaching Experience:

• Guest Lecturer, Biomaterials for Regenerative Medicine, BIOE 361, Stanford (2021, 2022)
• Guest Lecturer, The Tissue Microenvironment, BIOE 598, UIUC (2022)
• Guest Lecturer, Introduction to Materials Science and Eng, MSE 182, UIUC (2017 – 2020)
• Graduate Teaching Assistant, Introduction to Materials Science and Eng, UIUC (2017 – 2018)

Diversity and Service:

Visibility of minorities and underrepresented groups is an important component in creating an inclusive community that promotes diversity within STEM. As a member of the LGBTQA+ community, I have benefited from mentors who identify as LGBTQA+ and are able to share their experiences and provide a shining example of underrepresented groups in academia. LGBTQA+ members are significantly more likely to face mental health challenges and feelings of isolation that lead to departure from STEM and academia. Therefore, as a faculty member, I am committed to providing and participating in initiatives that provide mentorship to monitories and underrepresented groups, particularly at the intersection of LGBTQA+. As a graduate student at the University of Illinois, I was a graduate member of Out in STEM (oSTEM) and served on the award committee for the National Organization of Gay and Lesbian Scientists and Technical Professionals (NOGLSTP). Additionally, I participated in campus-wide efforts to engage underrepresented groups in STEM, such as the Girls’ Adventures in Math, Engineering, and Science summer camp. I also participated in mentorship programs of underrepresented groups to introduce undergraduates to STEM and research. As a faculty member, I intend to continue to work with local and national LGBTQA+ organizations to develop mentorship programs that connect underrepresented groups with established mentors in STEM. My experience with mentoring has reinforced the importance of visibility and ensuring that there are resources and safe spaces available to reduce the “leaky” pipelines.