Progranulin is expressed within motor neurons and promotes neuronal cell survival

Abstract

BackgroundProgranulin is a secreted high molecular weight growth factor bearing seven and one half copies of the cysteine-rich granulin-epithelin motif. While inappropriate over-expression of the progranulin gene has been associated with many cancers, haploinsufficiency leads to atrophy of the frontotemporal lobes and development of a form of dementia (frontotemporal lobar degeneration with ubiquitin positive inclusions, FTLD-U) associated with the formation of ubiquitinated inclusions. Recent reports indicate that progranulin has neurotrophic effects, which, if confirmed would make progranulin the only neuroprotective growth factor that has been associated genetically with a neurological disease in humans. Preliminary studies indicated high progranulin gene expression in spinal cord motor neurons. However, it is uncertain what the role of Progranulin is in normal or diseased motor neuron function. We have investigated progranulin gene expression and subcellular localization in cultured mouse embryonic motor neurons and examined the effect of progranulin over-expression and knockdown in the NSC-34 immortalized motor neuron cell line upon proliferation and survival.ResultsIn situ hybridisation and immunohistochemical techniques revealed that the progranulin gene is highly expressed by motor neurons within the mouse spinal cord and in primary cultures of dissociated mouse embryonic spinal cord-dorsal root ganglia. Confocal microscopy coupled to immunocytochemistry together with the use of a progranulin-green fluorescent protein fusion construct revealed progranulin to be located within compartments of the secretory pathway including the Golgi apparatus. Stable transfection of the human progranulin gene into the NSC-34 motor neuron cell line stimulates the appearance of dendritic structures and provides sufficient trophic stimulus to survive serum deprivation for long periods (up to two months). This is mediated at least in part through an anti-apoptotic mechanism. Control cells, while expressing basal levels of progranulin do not survive in serum free conditions. Knockdown of progranulin expression using shRNA technology further reduced cell survival.ConclusionNeurons are among the most long-lived cells in the body and are subject to low levels of toxic challenges throughout life. We have demonstrated that progranulin is abundantly expressed in motor neurons and is cytoprotective over prolonged periods when over-expressed in a neuronal cell line. This work highlights the importance of progranulin as neuroprotective growth factor and may represent a therapeutic target for neurodegenerative diseases including motor neuron disease.

Rescue of Progranulin Deficiency Associated with Frontotemporal Lobar Degeneration by Alkalizing Reagents and Inhibition of Vacuolar ATPase

“…Increasing production of GRN from the remaining wt allele is therefore a logical therapeutic approach. Based on the currently available data, the full-length GRN protein rather than the proteolytically processed granulin peptides is expected to exert the described beneficial neurotrophic and anti-inflammatory function (Kessenbrock et al, 2008;Van Damme et al, 2008;Ryan et al, 2009). However, even if GRN-associated FTLD-TDP would be caused by lack of GRN peptides, rather than by the GRN holoprotein, elevating their precursor would be beneficial, because this should also restore the amount of its cleavage products.…”

Progranulin Deficiency Decreases Gross Neural Connectivity But Enhances Transmission at Individual Synapses

“…Thus far, PGRN has been implicated in the regulation of neuronal survival (Van Damme et al, 2008;Ryan et al, 2009;Kleinberger et al, 2010), and treatment of neurons with exogenous PGRN has been shown to enhance neurite outgrowth (Van Damme et al, 2008;Gao et al, 2010). Despite this, an understanding of the role of PGRN in the development and maintenance of neural circuitry is still in its infancy.…”

Activity-dependent secretion of progranulin from synapses

“…In the adult brain, PGRN is expressed in microglia, in pyramidal neurons of the cortex and hippocampus, as well as in cerebellar Purkinje cells and spinal motor neurons (Petkau et al, 2010). PGRN has been shown to play a role in promoting neuronal survival, enhancing neurite outgrowth and regulating inflammation in the central nervous system (CNS) (Guo et al, 2010;Ryan et al, 2009;Tang et al, 2011;Van Damme et al, 2008;Xu et al, 2011). Interest in the regulation and function of PGRN in the brain has significantly increased following the discovery that mutations in the progranulin (also known as granulin) gene (GRN) are the major cause of autosomal dominant frontotemporal dementia (FTD) with tau-negative inclusions Bronner et al, 2007;Cruts et al, 2006;Gass et al, 2006;Mukherjee et al, 2006;Pickering-Brown et al, 2006;van der Zee et al, 2007).…”