Factor-Induced-Gene 4 (FIG4), also known as SAC3, was first cloned from a human immature myeloid cell line in 1996.[1, 2] The protein encoded by FIG4 is a phosphatase that regulates phosphatidylinositol 3,5-bisphosphate, a molecule critical buy Romidepsin for intracellular vesicle trafficking along the endosomal-lysosomal pathway. Previous studies have shown that FIG4 is abundantly expressed during neural development in mice and rats; FIG4 is expressed in neurons and myelin-forming cells in the central
and peripheral nervous systems, particularly in spinal ganglia sensory neurons and Schwann cells. Although FIG4 protein and mRNA levels are markedly diminished in neurons of the adult CNS, spinal cord injury induces upregulation of FIG4 in the adult spinal cord, and this is associated with accumulation of lysosomes in neurons and glia. FIG4 knockout mice and rats result in spongiform neurodegeneration with enlarged lysosomal vesicles, defective myelination and juvenile lethality.[5, 6] These findings suggest that expression
of FIG4 is required for neural development and is necessary to prevent neurodegeneration. Mutations of FIG4 cause Charcot-Marie-Tooth disease type 4J (CMT4J; MIM 611228), a severe form of peripheral neuropathy.[6, 7] Mutations of FIG4 may also lead to the development of familial and sporadic amyotrophic lateral sclerosis (ALS) (ALS11; MIM 609390). However, the localization of FIG4 in the human BTK inhibitor nervous system has not yet been immunohistochemically investigated. Abnormal accumulation and aggregation of disease-specific proteins are common features of several neurodegenerative diseases. Impairment of the endosomal-lysosomal and autophagy-lysosomal
pathways is one of the common pathomechanisms of various neurodegenerative diseases, including Alzheimer’s disease (AD), Parkinson’s disease (PD) and polyglutamine diseases. Recently, several investigators have reported that familial ALS-associated proteins (trans-activation response DNA protein 43 (TDP-43),[11-14] fused in sarcoma (FUS),[15, 16] optineurin,[17, 18] ubiquilin-2,[19, ifenprodil 20] charged mutivesicular body protein 2b (CHMP2B)[21, 22] and valosin-containing protein) are involved in inclusion body formation in various neurodegenerative diseases. These reports prompted us to investigate whether FIG4 is involved in a variety of neurodegenerative diseases, including TDP-43 proteinopathy (sporadic ALS and frontotemporal lobar degeneration). Using immunohistochemistry, we therefore examined the brains and spinal cords of patients with various neurodegenerative diseases and control subjects using anti-FIG4 antibody.