Regulation of hematopoietic stem cell niche aging by the sympathetic nervous system

PROJECT SUMMARY: Hematopoietic aging is associated with a decline in the regenerative capacity of hematopoietic stem cells (HSCs), leading to the development of blood disorders and loss of immune function. We have previously demonstrated that aging leads to sympathetic neuropathy of the BM and that premature loss of nerves or

adrenergic receptor β3 (Adrβ3) accelerated the appearance of intrinsic aging-like phenotypes in HSC. In contrast, supplementation of β3-adrenergic agonists to boost signaling in aged mice rejuvenated niche and HSC function. However, mechanisms downstream of the SNS that drive the phenotypic features of aging niche

and HSCs remain unclear. In the healthy BM, perivascular stromal cells containing all mesenchymal stem cell (MSC) activity are regulated by oscillatory signals from the SNS that control the mobilization of hematopoietic stem and progenitor cells into peripheral blood. BM MSCs comprise two distinct subpopulations: peri-arteriolar

MSCs (periMSC), directly innervated by the SNS, and peri-sinusoidal reticular MSCs (reticMSCs) denuded from innervation. Although reticMSCs are found away from sympathetic nerves, they are targeted by the SNS to mediate HSC maintenance and trafficking. Preliminary data supporting this application provide evidence that

aged reticMSCs exhibit significant alterations in redox signaling and glucose metabolism pathways that are controlled by the SNS. Furthermore, we have identified a potential mechanism of neural signal transmission in the niche that depends on connexin gap junctions and peri-arteriolar NADPH Oxidase (NOX). We show that

the generation of reactive oxygen species (ROS) by the NOX complex in MSCs depends on signals from the SNS and that targeting NOX, specifically in periMSCs, induced aging-like phenotypes in reticMSCs and HSCs. Based on our findings, we hypothesize that NOX-derived ROS transduce β-adrenergic signals via connexin gap

junctions and that loss of ROS transmission deregulates reticMSC homeostasis, leading to expansion of metabolically dysfunctional subsets that are unable to maintain HSCs. This hypothesis will be tested in two aims. In Specific Aim 1, we propose to define the mechanism of neural signal transduction by using a novel MSC

culture system and assess the role of connexins and ROS in stromal cell-to-cell communication using pharmacologic and genetic means. In Specific Aim 2, we will investigate how SNS-enabled stromal ROS homeostasis and mitochondrial metabolism alter MSC and niche function to regulate HSC aging. Our proposed

studies will identify new mechanisms of HSC aging and help devise therapeutic rejuvenation strategies to improve or prevent the course of age-associated hematopoietic diseases.