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The Role of Monocytes in Diabetic Retinopathy Pathogenesis

Peripheral blood cells are the circulating cellular components of blood consisting of red blood cells (erythrocytes), white blood cells (leukocytes), and platelets. White blood cells make up ~1% of all blood cells and each subpopulation has a specialized role in the immune system to safeguard against infection and injury.

Monocytes, characterized by the expression of the CD14 cell surface receptor are bone marrow-derived white blood cells that are part of the mononuclear phagocyte system, a component of the body’s innate immunity. During both homeostasis and inflammation, monocytes can leave the bloodstream and migrate into tissues where they can, in response to local factors (i.e., pro-inflammatory cytokines and chemokines), differentiate into macrophage or dendritic cell populations, which serve three key functions in the immune system- phagocytosis, antigen presentation, and cytokine production.

Lifeline® offers a wide range of high quality, purified peripheral blood mononuclear cells including:

Recent Research using Lifeline CD14+ Monocytes

Diabetic retinopathy (DR) is a debilitating eye condition, which affects the blood vessels in the retina resulting in vision loss and blindness in people with diabetes. There is an established correlation between leukocyte-retinal endothelial cell adhesion and retinal capillary damage. Upregulation of ICAM-1 adhesion molecules on endothelial cells triggered by high glucose levels in diabetes is thought to promote leukocyte (primarily monocytes) adhesion, stimulating local release of pro-inflammatory factors that disrupt the junctional integrity of the endothelial cells of the blood retinal barrier (BRB), allowing leukocytes to infiltrate the retina. A recent publication by Ibrahim and Colleagues sought to understand the molecular mechanism behind the hyperglycemia-driven monocyte response and retinal damage. Previous work by this group implicates the bioactive lipid metabolites of 12/15 Lipoxygenase (12/15-LO) in mediating this inflammatory response in DR but whether the 12/15-LO is attributed to the retinal endothelial cells or the monocytic/macrophagic cells is the focus of this most recent publication.

Lifeline’s Normal Human CD14+ Monocyte Cells were utilized with an in vitro model of the retinal endothelium in combination with in vivo knockout mouse studies to determine whether it is endothelial- or monocyte-derived 12/15-LO that plays a role in hyperglycemia-induced leukocyte adhesion and retinal endothelial barrier dysfunction. Several key pieces of evidence led the researchers to conclude that it is endothelial 12/15-LO responsible for this phenomenon.

  • 12/15- LO expression was observed in retinal microvascular endothelial cells (HRECs) but barely detectable in human monocyte-like U937 cells
  • leukocyte adhesion assay performed using Lifeline’s purified CD14+ monocytes with HRECs treated with high glucose resulted in a significant reduction in Transcellular Electrical Resistance (TER), which is indicative of BRB dysfunction; this confirms a causal link between leukocyte adhesion and loss of barrier integrity in DR
  • pharmacological inhibition and siRNA knockdown of 12/15-LO in HRECs resulted in decreased ICAM-1 expression, and concomitant reduction in hyperglycemia-induced leukocyte adhesion suggesting that endothelium-derived 12/15-LO activity and upregulation of ICAM-1 plays an essential role in mediating leukocyte adhesion and endothelial barrier dysfunction during DR

In summary, the data published by the authors demonstrated that high glucose levels in diabetes activates the 12/15-LO pathway in the retinal endothelial cells, which results in autocrine activation of the cells themselves to increase ICAM-1 expression on their surface. This upregulation of ICAM-1 promotes monocyte adhesion to the endothelium disrupting the BRB allowing the invasion of monocytes into the retina to produce the retinal capillary damage observed in DR. Because the interaction between monocytes and the endothelium is a key early event in DR progression, targeting the 12/15-LO pathway in endothelial cells may facilitate the development of more precisely targeted therapeutic strategies to treat the disease.

Have you used Lifeline’s CD14+ Monocytes in your research? If so, we would love to feature your study here on our blog!

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