Gene expression profile of DAP12 knockdown THP-1 cells following exposure to phorbol 12-myristate 13-acetate

Nasu-Hakola disease (NHD), also designated polycystic lipomembranous osteodysplasia with sclerosing leukoencephalopathy (PLOSL), is a rare autosomal recessive disorder characterized by progressive presenile dementia and formation of multifocal bone cysts, caused by a loss-of-function mutation of DAP12 or TREM2. TREM2 and DAP12 constitute a receptor/adaptor complex expressed on osteoclasts, dendritic cells, macrophages, monocytes, and microglia. At present, the precise molecular mechanisms underlying development of leukoencephalopathy and bone cysts in NHD remain largely unknown. We established THP-1 human monocyte clones that stably express small interfering RNA (siRNA) targeting DAP12 for serving as a cellular model of NHD. Genome-wide transcriptome analysis identified a set of 22 genes consistently downregulated in DAP12 knockdown cells. They constituted the molecular network closely related to the network defined by cell-to-cell signaling and interaction, hematological system development and function, and inflammatory response, where NF-kappaB acts as a central regulator. These results suggest that a molecular defect of DAP12 in human monocytes deregulates the gene network pivotal for maintenance of myeloid cell function in NHD. We found that both DAP12 knockdown and control clones were capable of equally responding to phorbol 12-myristate 13-acetate (PMA), a known inducer of morphological differentiation of THP-1 cells, by exhibiting almost similar gene expression profiles between both, following a 24-hour exposure to 50 nM PMA. The siRNA vector construct targeting the DAP12 sequence (SI) and the control vector construct targeting the scrambled sequence (SCR) were generated by using GeneClip U1 Hairpin cloning system (Promega). The vectors were transfected in THP-1 cells by using Lipofectamine LTX reagent. The stable cell lines were selected by incubating them for approximately two months in the feeding medium with inclusion of 200 microgram/ml Hygromycin B. Then, two SI clones named SI5 and SI17, in addition to two SCR clones named SCR1 and SCR4, were selected by limiting dilution of the cells in a manner of a single cell per well plated in a 96-well cell culture plate. Microarray data for clones SCR4 and SI17 submitted in this Series.