Whole body deletion of Gpr68 does not change hematopoietic stem cell function

Xiaofei He; Caleb Hawkins; Lauren Lawley; Kennedy Freeman; Tra Mi Phan; Jiajia Zhang; Yan Xu; Jing Fang

doi:10.1016/j.scr.2020.101869

Whole body deletion of Gpr68 does not change hematopoietic stem cell function

Stem Cell Res. 2020 Jun 20:47:101869. doi: 10.1016/j.scr.2020.101869. Online ahead of print.

Authors

Xiaofei He¹, Caleb Hawkins¹, Lauren Lawley¹, Kennedy Freeman¹, Tra Mi Phan¹, Jiajia Zhang², Yan Xu³, Jing Fang⁴

Affiliations

¹ Department of Drug Discovery and Biomedical Sciences, University of South Carolina College of Pharmacy, Columbia, SC, USA.
² Department of Epidemiology and Biostatistics, University of South Carolina Arnold School of Public Health, Columbia, SC, USA.
³ Department of Obstetrics and Gynecology, Indiana University School of Medicine, Indianapolis, IN, USA.
⁴ Department of Drug Discovery and Biomedical Sciences, University of South Carolina College of Pharmacy, Columbia, SC, USA. Electronic address: fang8@cop.sc.edu.

Abstract

G protein-coupled receptor 68 (GPR68) responds to extracellular protons, thus called the proton-sensing G protein-coupled receptor (GPCR), leading to activation of the phospholipase C-β (PLCβ)/calcium (Ca²⁺) pathway or the adenylyl cyclase (AC)/cyclic AMP (cAMP) pathway. We recently found that whole body deletion of Gpr68 (Gpr68^-/- mice) reduced the number of B lymphocytes with age and during hematopoietic regeneration, such as in response to fluorouracil (5-FU) administration. This prompted us to characterize the hematopoietic stem cell (HSC) phenotype in Gpr68^-/- mice. Despite high level of Gpr68 protein expression on HSC in bone marrow (BM), the pool size of HSC was unaltered in Gpr68^-/- mice either under steady state or upon stress, including aging and 5-FU treatment. HSC from Gpr68^-/- mice exhibited comparable cellular features, such as cell cycle quiescence and cell survival. HSC from Gpr68^-/- mice also exhibited comparable competitiveness after serial transplantation. Surprisingly, cytosolic Ca²⁺ accumulation was increased in HSC from Gpr68^-/- mice. In contrast, cAMP levels were reduced in hematopoietic stem and progenitor cells (HSPC) from Gpr68^-/- mice. Intriguingly, we found high level of Gpr68 protein expression on non-hematopoietic cells in BM, especially endothelial cells that function as HSC niche. In addition, expression of other proton-sensing GPCR was upregulated in HSPC from Gpr68^-/- mice. Our studies suggest that Gpr68^-/- mice display insignificant phenotype on HSC biology, possibly due to the function of Gpr68 in non-hematopoietic cells and/or the compensatory effects from other proton-sensing GPCR.

Keywords: G protein-coupled receptor 68; Hematopoietic stem cells; Proton-sensing G protein-coupled receptors.

Abstract

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