Stromal cell-derived growth factor-1α (SDF-1α) is a member of the CXC chemokines and interacts with the G protein, seven-transmembrane CXCR4 receptor. SDF-1α acts as a chemoattractant for immune and hemopoietic cells. The Tac1 gene encodes peptides belonging to the tachykinin family with substance P being the predominant member. Both SDF-1α and Tac1 peptides are relevant hemopoietic regulators. This study investigated the effects of SDF-1α on Tac1 expression in the major hemopoietic supporting cells, the bone marrow stroma, and addresses the consequence to hemopoiesis. Reporter gene assays with the 5′ flanking region of Tac1 showed a bell-shaped effect of SDF-1α on luciferase activity with 20 ng/ml SDF-1α acting as stimulator, whereas 50 and 100 ng/ml SDF-1α acted as inhibitors. Gel shift assays and transfection with wild-type and mutant IκB indicate NF-κB as a mediator in the repressive effects at 50 and 100 ng/ml SDF-1α. Northern analyses and ELISA showed correlations among reporter gene activities, mRNA (β-preprotachykinin I), and protein levels for substance P. Of relevance is the novel finding by long-term culture-initiating cell assays that showed an indirect effect of SDF-1α on hemopoiesis through substance P production. The results also showed neurokinin 1 and not neurokinin 2 as the relevant receptor. Another crucial finding is that substance P does not regulate the production of SDF-1α in stroma. The studies indicate that SDF-1α levels above baseline production in bone marrow stroma induce the production of substance P to stimulate hemopoiesis. Substance P, however, does not act as autocrine stimulator to induce the production of SDF-1α. This study adds SDF-1α as a mediator within the neural-immune-hemopoietic axis.

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Human mesenchymal stem cells (MSCs) are easy to expand, are relatively safe, and can be transplanted in allogeneic recipients as off-the-shelf cells. MSCs can be induced to form functional peptidergic neurons and express the neurotransmitter gene, TAC1. Expression of TAC1 requires that the repressor gene, RE-1 silencing transcription factor (REST), is decreased. This study investigated the molecular pathway in TAC1 induction as MSCs differentiated into neurons and then applied the findings in a model of spinal cord injury (SCI) in zebrafish. We studied the developmental roles of the 2 cAMP response element (CRE) sites: CRE1 and CRE2. Activator protein-1 (AP-1) binding site overlaps with CRE2 (CRE2/AP-1). Reporter gene studies with the 5¢ regulatory region of TAC1 containing wild-type or mutant CRE sites and, parallel studies with ectopically expressed inhibitor of cAMP proteins (inducible cAMP early repressor) indicated that CRE1 and CRE2/AP-1 are activated at days 6 and 12, respectively. Studies with protein kinase-A (PKA) and Jun N-terminal kinase ( JNK) inhibitors in the reporter gene studies, chromatin immunoprecipation assay, and ectopic expression of REST indicated the following pathways: Decrease of REST activated upstream c-Jun N-terminal kinase (JNK). In turn, JNK activated ATF-2 and AP-1 for interaction with CRE1 and CRE2/AP-1, respectively. To apply the finding to SCI, we transplanted 6-day-induced MSCs in transgenic HB9-GFP zebrafish larvae with SCI, in the presence or absence of JNK inhibitors. Imaging and functional studies showed significant improvement in the fish. The repair mechanism involved the activation of JNK. The findings have long-term implications for SCI repair with MSCs.