Progranulin (PGRN) expression in ALS: an immunohistochemical study

Mutations in the gene progranulin (PGRN) were recently identified as the cause of some forms of frontotemporal dementia with ubiquitin-positive intraneuronal inclusion pathology (FTLD-U). The DNA-binding protein, TDP-43, was determined to be a component of these ubiquitinated inclusions in FTLD-U and amyotrophic lateral sclerosis (ALS) with dementia (ALS-D). These findings raise many interesting questions as to the shared pathology and possible common pathologic process between ALS and FTLD-U. This study examines the immunoexpression of PGRN in ALS patients using immunohistochemical analysis of post-mortem tissue. Available brain and spinal cord sections of eight ALS patients, including one case with severe dementia, and eighteen control-aged brains were stained with anti-PGRN antibodies. We found increased staining for PGRN in motor tracts with vacuolar degeneration and glial cells in ALS sample spinal cord and brainstem sections compared to controls. Variable upper motor neuron staining and reactive glia were seen in ALS motor cortex samples. Frontal lobe and hippocampal sections showed no consistent differences from control tissues with the exception of the ALS-dementia case, which showed PGRN immunoexpression in non-motor cortical areas. These results describe a pattern of increased PGRN expression in areas of active degeneration in ALS. The meaning of this association is unclear, but may indicate a potential role for PGRN in the variable expression of motor and cognitive deficits in the ALS-FTD spectrum.