The role of resistin-like gamma expressed by haematopoietic stem cells in controlling their maintenance and commitment to differentiation

Hazzazi, Mohannad (2021). The role of resistin-like gamma expressed by haematopoietic stem cells in controlling their maintenance and commitment to differentiation. University of Birmingham. Ph.D.

Preview

Hazzazi2021PhD.pdf
Text - Accepted Version
Available under License All rights reserved.
Download (5MB) | Preview

Abstract

Haematopoietic stem cells (HSC) are at the top of a hierarchy of cell commitment, proliferation, and differentiation that leads to the life-long production of the functional cell types that constitute the blood. The maintenance of HSC is tightly controlled by an interplay between cell intrinsic and extrinsic mechanisms, the latter including the bone marrow niche environment and systemic factors. One intrinsic factor, the transcriptional regulator MYB, is important in normal HSC maintenance and in the initiation of haematological disease and ageing. From genetic manipulation and RNA-seq experiments, the Resistin-like gamma (RETNL $\gamma$ ) gene has emerged as a predominant target of the action of MYB. This project involves the investigation of the expression and function of the RETNL $\gamma$ gene and protein in HSC.
RETNL $\gamma$ is a member of a small family of Resistin-related proteins that appear to act as soluble mediators of a number of biological processes, working by binding to cognate receptors. Very little is known about RETNL $\gamma$ apart from a demonstrated expression in several tissues, including bone marrow. This project seeks to determine the nature of RETNL $\gamma$ expression in the HSC compartment at the RNA and protein level. In order to investigate the function of RETNL $\gamma$ in HSC in the bone marrow, a mouse knock out (KO) of the RETNL $\gamma$ gene was used in a combination of in vitro and in vivo assays to measure the consequences of absence of the protein.
The RETNL $\gamma$ gene was found to be expressed throughout the haematopoietic hierarchy, the level of expression varying widely with mature myelomonocytic cells and HSC expressing the highest and lowest levels, respectively. Interestingly, comparing males and females, significantly lower expression of RETNL $\gamma$ RNA was noted in the most immature HSC and in
megakaryocytes. RETNL $\gamma$ protein levels correlated with the RNA expression data. The gender-specific differences in RETNL $\gamma$ RNA expression were reflected in corresponding differences in HSC numbers in the bone marrow. Transcriptome analysis of female HSC showed that the absence of RETNL $\gamma$ results in significant gene expression differences, particularly in terms of increased expression of immune- and stress-related genes in the knockout, which were not affected in males. Attempts to rescue the effects of the absence of RETNL $\gamma$ in knockout female HSC were unsuccessful in that the normal level of affected genes could not be restored, most likely because of a failure to achieve physiological levels of RETNL $\gamma$ activity.
Overall, the results point to a female-specific function of RETNL $\gamma$ in HSC, which opens up a whole new area of research into the mechanisms at play, both in terms of the role of RETNL $\gamma$ and the way in which this is influenced by the gender background.