493-P: Cerebral Spinal Fluid Supports Calvaria Bone Marrow to Sustain Hematopoiesis and Protect the Retina following Acute Ischemia/Reperfusion Injury and in Diabetic Retinopathy

Introduction and Objectives: Hematopoietic cells emanate from multiple bone marrow (BM) compartments and support microvascular repair. Calvaria BM has a unique exposure to cerebrospinal fluid (CSF) which may modulate hematopoiesis, whereas this exposure does not occur for long bones. We asked if hematopoiesis differed between calvaria and long bones and if so, how this impacted diabetic retinopathy (DR) or the response to ischemia/reperfusion (I/R) injury. Because oxysterols and hematopoiesis have been linked, oxysterol content of paired plasma and CSF were compared.

Methods: In 12-month db/db mice, flow cytometry, micro CT, mass spectrometry (MS) and IHC were used to investigate the impact of type 2 diabetes (T2D) on distinct BM compartments and on DR. Recruitment of BM-derived cells into retina after I/R injury was assessed using in vivo cell labelling of each BM compartment in Kikume Green-Red photoconvertible fluorescent protein (KIKGR) reporter mice.

Results: In db/db mice, calvaria in contrast to tibia underwent slower bone deterioration and less vascular degeneration while sustaining physiological hematopoiesis as evident by elevated levels of myeloid angiogenic cells (MACs), a key vascular reparative BM population. Calvaria was the source of reparative MACs following I/R injury, whereas long bones provided pro-inflammatory monocytes to the retina. MS demonstrated that CSF of db/db mice, but not serum, contained high levels of the neurotropic and anti-inflammatory oxysterols, 22-hydroxycholesterol and 27-hydroxycholesterol.

Conclusion: CSF-derived oxysterols, selectively accessible to the calvaria BM compartment but not long bones, preserves physiological hematopoiesis despite chronic T2D. Calvaria provides a source of reparative cells to the retina following acute injury and retards DR, whereas the long bones primarily provide pro-inflammatory monocytes.