Resilient Calvarial Bone Marrow Supports Retinal Repair in Type 2 Diabetes

Area of Science:

• Immunology
• Endocrinology
• Bone Biology

Background:

• Type 2 diabetes (T2D) often compromises bone marrow function and structural integrity.
• The calvarium's unique anatomical relationship with cerebrospinal fluid (CSF) suggests a distinct microenvironment.
• The role of calvarial bone marrow in immune surveillance, particularly in the context of chronic diseases like T2D, is not well understood.

Purpose of the Study:

• To investigate the structural and functional integrity of calvarial bone marrow in T2D.
• To characterize the biochemical milieu of the calvarium, including oxysterol profiles in CSF.
• To determine the contribution of calvarial bone marrow to immune cell mobilization, specifically for retinal defense.

Main Methods:

• Micro-computed tomography (micro-CT) for assessing calvarial bone structure.
• Mass spectrometry for profiling oxysterols in CSF.
• Analysis of CSF from human subjects with idiopathic intracranial hypertension (IIH).
• Quantification of myeloid angiogenic cells (MACs) and neutrophils mobilized from bone marrow.

Main Results:

• Calvarial bone marrow in T2D mice maintained structural integrity and hematopoietic capacity, unlike long bone marrow.
• Murine and human CSF showed elevated levels of neurotrophic and anti-inflammatory oxysterols (e.g., 22-OHC, 27-OHC, 7-HOCA).
• Calvarial bone marrow was a primary source of MACs and neutrophils, mobilizing them ~20-fold higher than long bones.

Conclusions:

• Calvarial bone marrow possesses unique protective mechanisms, preserving structure and function in T2D.
• A conserved neuroprotective oxysterol signature in CSF suggests a species-wide protective role.
• Calvarial bone marrow is a critical reservoir for immune cells essential for retinal immune defense.