Role of Hepatocyte Growth Factor in Endothelial-Dependent Hematopoietic Stem Cell Regeneration

Hematopoiesis is tightly regulated by the niche and highly sensitive to a variety of genotoxic stressors. The mechanisms responsible for the repair and regeneration of hematopoietic stem cells (HSCs) are poorly understood. Endothelial cells (ECs) are an essential component of the bone marrow microenvironment that provide regenerative signals for HSCs after injury; however, the identity of these signals remain largely unknown. We utilized RNA sequencing and a bioinformatics approach to identify hepatocyte growth factor (HGF) as an endothelial-derived mediator of HSC regeneration. HGF gene expression was 7.6-fold higher in arterial-derived ECs (HAEC) that regenerate functional long-term HSCs (CD150⁺Lineage^loSca1⁺Kit⁺ cells; CD150⁺LSK cells) compared to venous ECs (HUVEC) that support only hematopoietic progenitors. Furthermore, the HSC-supportive HAECs secreted up to 25 pg/mL HGF into conditioned media, whereas HGF was undetectable in media conditioned by HUVEC. To directly test the role of HGF in HSC regeneration, we supplemented co-cultures of irradiated bone marrow cells and primary ECs with recombinant HGF. Addition of HGF was sufficient to augment CD150⁺LSK cell regeneration up to 20-fold by HUVEC. This effect was abolished by treatment with the Met-specific small molecular inhibitor, PF04217903. Importantly, neither the addition of HGF alone to irradiated hematopoietic cells nor spiking HUVEC-conditioned media with HGF improved HSC regeneration in the absence of an EC monolayer. Together, these results indicate that HGF activates a signaling loop in ECs that supports HSC regeneration.