Author ORCID Identifier

https://orcid.org/0000-0003-1012-5811

Date Available

12-16-2024

Year of Publication

2022

Document Type

Doctoral Dissertation

Degree Name

Doctor of Philosophy (PhD)

College

Medicine

Department/School/Program

Toxicology and Cancer Biology

Advisor

Dr. Ying Liang

Abstract

Hematopoietic stem cells (HSC), which are a rare population of cells existing in human circulating blood and bone marrow, can form the whole-blood system by their self-renewal capacity and differentiation ability. Sex dimorphism can be found in hematopoietic stem and progenitor cells, and in the development of hematopoietic lineages. Also, males are at higher risk and have a worse prognosis for most hematologic malignancies than females. Under normal conditions, the number of circulating progenitor cells in women is lower than in men. Furthermore, female mice have a higher rate of HSC division than male mice. A dramatic gender difference exists in leukemia patients and the normal hematopoietic systems. However, the molecular mechanism underlying normal hematopoiesis sex dimorphism is largely unknown.

In first project, we identified that Latexin (Lxn), which is a natural inhibitor of carboxypeptidase A, functions differently between male and female hematopoietic stem cells. Lxn deletion can increase the survival and repopulation capacity of HSCs in female mice. While no changes in HSC function or hematopoiesis in Lxn knockout male mice. Furthermore, although thrombospondin 1 (Thbs1) is the downstream target of Lxn in female HSCs, Thbs1 expression was very low in male HSCs. We identified several microRNAs (miR) that are differentially expressed in a gender-specific manner by conducting miRNA-qPCR in HSCs. MiR98-3p is highly expressed in male cells and contributes to Thbs1 downregulation in male HSCs. Thus, Lxn-Thbs1 signaling functions differently between male and female HSCs. In conclusion, gender-specific expression of miR98-3p contributes to the low expression of Thbs1, thus abrogating the effect of Lxn in the male hematopoietic system.

In second project, we first identified that male mice have more HSCs than female mice. By conducting two sex/gender mismatch transplantation experiments, we found that the male niche provides better hematopoietic engraftment, and male donor cells engraft better than female donor cells. Furthermore, by performing the single-cell RNA sequencing and co-culture HSC with MSC assay, we identified more Mesenchymal stem cells (MSCs) in male mice, and male MSCs better support HSC function. Thus, the male niche better support HSCs engraftment. Based on the differently expressed genes between male and female MSCs, we further discovered that male MSCs secrete more CXCL12, which may underlie the increased hematopoietic regeneration. We are currently investigating the mechanism underlying CXCL12 differential expression in the male/female niche by focusing on the Kdm5c gene. Kdm5c is a gene on the X chromosome that has escaped Xist inactivation. Female cells, therefore, express twice as much as male cells. It specifically demethylates H3K4me3/me2 and inhibits gene transcription. By using Chip-qPCR, we found that Kdm5c was highly enriched in the CXCL12 promoter in female MSCs compared to male MSCs, leading to the increased level of demethylated H3K4me3, thus reducing the expression of CXCL12. In conclusion, a lower level of KDM5C in male MSC leads to higher expression of CXCL12, which promotes HSC engraftment and maintenance in male niche.

These studies provide mechanistic insights about sex difference in hematopoiesis and niche in normal and stress conditions. Both research and clinical therapy on hematopoiesis will be benefited greatly from uncovering the differences between males and females.

Digital Object Identifier (DOI)

https://doi.org/10.13023/etd.2022.417

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