Corpora Amylacea in Aging Brain and Age-Related Brain Disorders

Abstract

Corpora amylacea (CA) are glycoprotein-based hyaline-like bodies that accumulate in normal aging brain, and to an even greater extent, in the brains of patients suffering from a variety of neurodegenerative disorders. Although many of the histochemical, tinctorial and structural properties of CAs have been described for more than a century and a half since their discovery, their pathogenic mechanisms, their subcellular origins and their functions are still debated. Two main theories have been advanced to explain the formation of CA, respectively the vascular and the metabolic theories, although pathogenically both mechanisms can be involved. The exact cellular source of CA in the nervous system is still under debate, although both a neuronal and glial origin has been suggested due to the presence of cell specific proteins. CAs contain around 90% glucose polymers (polyglucosan or polysaccharides), 3% phosphates and 5% proteins, most of them being aging or stress-related proteins. Ultrastructurally, CAs were described as masses of randomly oriented short linear electron-dense areas, situated in the cytoplasm of fibrous astrocytes, mainly in their distal processes. In transmission light microscopy they appear as circular bodies ranging from less than 2 µm to about 20 µm in diameter, with smooth surface or ragged appearance that typically have a concentric laminated or target-like patterns, with the cores staining rather more densely than the periphery. Besides their presence in aging brain, in many neurodegenerative disorders some similar structures called polyglicosan bodies, are morphologically indistinguishable from normal CAs, and were described in: Anderson’s disease, adult polyglucosan body disease, inflammatory demyelinating polyneuropathy, diabetic neuropathy, and in the neurons of patients with Lafora progressive myoclonus epilepsy. The differential diagnosis may include all the neuropathological diseases characterized by the production of peculiar materials with special morphology in the elderly. All together, these data come to show that these “enigmatic bodies” are far from being completely understood, thus further investigations are needed to better explain the brain aging and the pathogenesis of different degenerative neurological diseases, and perhaps they could provide novel therapeutic targets to counteract age-related brain disorders.