The calvarium bone marrow responds to acute retinal injury and is resilient to chronic diabetes compared to long bone marrow.

Abstract

Purpose : Hematopoiesis actively changes locations during development and is impacted by the microenvironment of each distinct bone marrow (BM) compartment. In adulthood, hematopoiesis, and BM cells mobilization are influenced by the presence of acute injury and chronic disease. We asked whether hematopoiesis in flat bones such as the calvarium was different than in long bones (LBs) during physiological post-natal development, following acute ischemic retinal injury, and in chronic injury as seen in type 2 diabetes (T2D).

Methods : Using flow cytometry, we compared hematopoiesis in the calvarium and LBs at postnatal day (P) 7, 14, and 21. The competitive repopulation (CR) assay was used to determine whether BM cells obtained from the calvarium or LBs of mice at these three time points reconstituted lethally irradiated mice faster. Recruitment of BM-derived cells into the retina after ischemia/reperfusion (I/R) injury was assessed using in vivo cell labelling of each BM compartment in Kikume Green-Red photoconvertible fluorescent protein (KIKGR) reporter mice. Flow cytometry, microCT, mass spectrometry and IHC were used to investigate the impact of T2D on the distinct BM compartments.

Results : The proportion of hematopoietic stem/progenitor cells (HSPCs) in the calvarium was significantly higher than that of the LBs at P7 and P14 but not at P21. The CR studies demonstrated that the calvaria marrow provides an environment more supportive of HSPCs survival following radiation injury. Calvaria marrow contributed more neutrophils and reparative myeloid angiogenic cells (MACs) to the retina than did the LBs following I/R injury. In db/db mice, the calvarium underwent slower bone deterioration, reduced fat buildup and vascular degeneration while sustaining hematopoiesis and maintaining high levels of MACs and HSPCs compared to the LBs. Mass Spectrometry confirmed that the calvarium contained neurotropic and anti-inflammatory oxysterols arising from the cerebral spinal fluid (CSF).

Conclusions : Our results demonstrate that the calvarium provided more reparative cells to the injured retina and was more resilient to chronic metabolic insult of T2D as supported by sustained HSPC function, compared to LBs. This unique resilience of the calvarium may be due to the supply of CSF-derived neuroprotective/anti-inflammatory agents that selectively bathes the calvarium compartment.

This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.