The Matrix Receptor CD44 Is Present in Astrocytes Throughout the Human CNS and Accumulates in Hypoxia and Seizures

In the mammalian isocortex CD44, a cell surface receptor for extracellular matrix molecules, is present in pial-based and fibrous astrocytes of white matter, but not the protoplasmic astrocytes. In the hominid isocortex, CD44+ astrocytes comprise the subpial “interlaminar” astrocytes, sending long processes into the cortex. The hippocampus also contains similar astrocytes. We have examined all levels of the human CNS and found CD44+ astrocytes in every region. Astrocytes in white matter and astrocytes that interact with large blood vessels, but not capillaries in gray matter, are CD44+, the latter extending long processes into the parenchyma. Motor neurons in the brainstem and spinal cord, such as oculomotor, facial, hypoglossal, and in the anterior horn of the spinal cord, are surrounded by CD44+ processes, contrasting with neurons in the cortex, basal ganglia and thalamus. We found CD44+ processes that intercalate between ependymal cells to reach the ventricle and that show a location-specific presence. We also found a CD44+ astrocyte in the molecular layer of the cerebellar cortex. Protoplasmic astrocytes, which do not normally contain CD44, acquire it in pathologies like hypoxia and seizures.