Background:
Diabetes induces chronic vascular inflammation that reshapes the bone marrow niche and promotes inflammatory myelopoiesis (1). Vascular cell adhesion molecule-1 (VCAM-1), a key mediator of endothelial activation and leukocyte recruitment, is upregulated under hyperglycemic conditions and contributes to vascular dysfunction. However, its role in sprouting bone marrow endothelial cells and its systemic dynamics during diabetic inflammation remain poorly defined.
Hypothesis/Objective:
We aim to systematically investigate VCAM-1 expression and function across scales, combining high-resolution microscopy with whole-body imaging (SPECT/CT)(2), and evaluate how endothelial VCAM-1 signaling influences inflammatory myeloid cell production in diabetes.
Methods:
Diabetes was induced in C57BL/6J and AplnCreER;Rosa26ZsGreen/+ reporter mice using high-fat diet (HFD) and streptozotocin (STZ). qPCR quantified vcam expression in apelin⁺ endothelial cells. Flow cytometry and histology characterized bone marrow myeloid progenitors, circulating leukocytes, and VCAM-1⁺ endothelial populations. Intravital microscopy was used to assess vascular density, sprouting angiogenesis, and VCAM-1 expression at single-cell resolution in calvarial bone marrow. Whole-body SPECT/CT imaging was performed to evaluate VCAM-1 distribution in vivo and validated by gamma counting.
Results:
Hyperglycemia profoundly alters the bone marrow microenvironment, promoting a shift toward increased myelopoiesis, as reflected by elevated leukocytosis and heightened systemic inflammatory output. This suggests that chronic metabolic stress drives hematopoietic skewing toward the myeloid lineage, contributing to inflammation-associated complications. At the molecular level, real time PCR analysis revealed a significant upregulation of vcam-1 expression in apelin⁺ endothelial cells, highlighting the activation of a specific endothelial subpopulation associated with angiogenic and remodeling processes. This increase in VCAM-1, a key adhesion molecule involved in leukocyte recruitment and endothelial activation, points to an enhanced inflammatory phenotype within the bone marrow vascular niche under diabetic conditions. Flow cytometry and histological analyses further supported these findings by demonstrating a clear expansion of bone marrow endothelial cell populations in diabetic mice. In addition to increased cell numbers, there was a marked elevation in VCAM-1 expression across endothelial cells, indicating not only structural but also functional remodeling of the vascular compartment. These changes suggest that hyperglycemia induces both proliferation and activation of endothelial cells, thereby reinforcing a pro-inflammatory microenvironment. Intravital two-photon microscopy provided real-time, high-resolution visualization of these alterations in vivo. Diabetic bone marrow exhibited increased vascular density, along with enhanced sprouting angiogenesis, indicative of active vascular remodeling. Importantly, these newly formed and remodeled vessels showed elevated VCAM-1 expression, further confirming the presence of an activated and inflamed endothelium. This vascular expansion likely facilitates increased trafficking and retention of immune cells, thereby sustaining the observed myelopoietic bias. At the whole-body level, SPECT imaging validated these observations by revealing a significantly increased VCAM-1 signal in diabetic mice. The signal was particularly pronounced in the femoral region, consistent with localized vascular activation within major hematopoietic sites. This non-invasive imaging approach highlights the systemic impact of hyperglycemia while also pinpointing specific anatomical regions of endothelial activation.
Conclusion:
These findings identify VCAM-1 as a key regulator of diabetes-induced vascular remodeling and inflammatory myelopoiesis within the bone marrow niche. Multiscale imaging reveals that VCAM-1 upregulation in sprouting endothelial cells is associated with enhanced vascular expansion and systemic inflammatory activation. Targeting VCAM-1 mediated endothelial signaling may therefore represent a promising strategy to modulate bone marrow driven inflammation and mitigate diabetic vascular complications.
Image/Figure:
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Image/Figure Caption:
Figure 1. Increased VCAM-1 expression in femoral and calvarial bone marrow in diabetes across multiple imaging scales.
(A) Representative two-photon microscopy images of the calvarial bone marrow showing increased VCAM-1 expression, along with CD31⁺ endothelial cells and Apln⁺ vascular structures, in diabetic mice compared to controls.
(B) Real-time PCR quantification of Vcam-1 relative expression on Apln⁺ blood vessels, demonstrating elevated levels in diabetic mice.
(C) Flow cytometry analysis demonstrating higher VCAM-1 expression in bone marrow endothelial cells from diabetic mice.
(D) Representative SPECT image showing the distribution of 99mTc-cAbVCAM1-5 in the skeletal system.
(E) Gamma counter analysis confirming increased accumulation of 99mTc-cAbVCAM1-5 in diabetic mice.
Author
Narmeen Haj
Technion Israel Institute of Technology