Expression of sulfatide in rodent CNS - not only restricted to myelin

Abstract

Sulfatide is an acidic glycosphingolipid and a component of myelin in the nervous system proposed to be involved in maintenance of the myelin structure and thereby its function. Sulfatide is also a commonly used marker for detection of oligodendrocyte progenitor cells in cultures as well as in tissues. Previous studies have, however, indicated that sulfatide might also be expressed in non-myelin-forming cells in the brain. The aim of this study was to elucidate the existence of sulfatide beyond oligodendrocytes in the CNS by combining immunohistochemistry and lipid analyses. Sulfatide expression was analysed in primary astrocyte cultures and in adult rodent brain tissue. To improve detection of sulfatide-positive cells in tissues, the detergent treatment was minimised to avoid extraction of the glycosphingolipid antigen and confocal microscopy was used for examination. In primary cultures, a minor population of sulfatide-positive astrocytes was detected immunohistochemically and the amount of sulfatide was quantified by lipid analyses. Sulfatide was located intracellularly in these astrocytes, in contrast to the cell plasma membrane association and external exposure in myelin. Subpopulations of sulfatide-positive astrocytes were also found in vitro, in rat and mouse brain tissue. Moreover, selected neurons expressed sulfatide in the investigated brain areas; cerebral cortex, hippocampus and cerebellum. An arylsulfatase A (ASA) null mutation mouse model, unable to degrade sulfatide, was used to facilitate the detection of sulfatide-expressing cells. This tissue showed an extensive accumulation of sulfatide in neurons, which indicates a higher turnover of sulfatide in neurons compared to astrocytes. Metachromatic leukodystrophy (MLD) is a human disease caused by defects in the ASA enzyme followed by extensive sulfatide accumulation in white matter and demyelination. Neurological symptoms are the most pronounced, while adult patients have initial psychiatric symptoms that have raised the question if other cells are involved in the progression of the disease. The findings in this study indicate that neurons might be those other cells. In conclusion, this thesis provides evidence for the expression of the myelin-associated glycosphingolipid - sulfatide - also in astrocytes and neurons in adult rodent brain. The role of sulfatide in the various cells remains an open question but its existence supports multipotential function, which might be considered to contribute to the symptoms of MLD.