Mesenchymal stromal cells (MSCs) transiently transfected with notch1 intracellular domain (NICD) are beneficial for neurological disorders as observed in several preclinical studies. Extracellular matrix (ECM) derived from NICD-transfected MSCs has been previously shown to support in vitro neural cell growth and survival better than that of un-transfected MSCs. To understand the underlying mechanism(s) by which NICD-transfected MSC-derived ECM supports neural cell growth and survival, we investigated the differences in NICD-transfected MSC- and MSC-derived ECM protein quantity and composition. 14 11 2013 8 11 e79283 e79283 16 11 2013 © 2013 Harvey et al This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are properly credited. Abstract Mesenchymal stromal cells (MSCs) transiently transfected with notch1 intracellular domain ( NICD ) are beneficial for neurological disorders as observed in several preclinical studies. Extracellular matrix (ECM) derived from NICD -transfected MSCs has been previously shown to support in vitro neural cell growth and survival better than that of un-transfected MSCs. To understand the underlying mechanism(s) by which NICD -transfected MSC-derived ECM supports neural cell growth and survival, we investigated the differences in NICD -transfected MSC- and MSC-derived ECM protein quantity and composition. To compare the ECM derived from MSCs and NICD -transfected MSCs, the proteins were sequentially solubilized using sodium dodecyl sulfate (SDS) and urea, quantified, and compared across four human donors. We then analyzed ECM proteins using either in-gel digests or in-solution surfactant-assisted trypsin digests (SAISD) coupled with reverse phase nano-liquid chromatography and tandem mass spectrometry (nLC-MS/MS). Analyses using nLC-MS/MS identified key components of ECM from NICD -transfected MSCs and un-transfected MSCs and revealed significant differences in their respective compositions. This work provides a reproducible method for identifying and comparing in vitro cell-derived ECM proteins, which is crucial for exploring the mechanisms underlying cellular therapy. status released display-pdf yes is-olf no is-manuscript no is-preprint no is-journal-matter no is-scanned no is-retracted no Received 2013 Jun 26; Accepted 2013 Sep 27; Collection date 2013. Introduction SB623 is a cell therapy product comprised of human bone marrow-derived mesenchymal stromal cells (MSCs) transiently transfected with a notch1 intracellular domain ( NICD )-expressing-plasmid. SB623 is currently in FDA-approved Phase I/IIa clinical testing for ischemic stroke. SB623 has been shown to improve functional behavior deficits and reduce neural cell loss in stroked rats, however governing biological mechanisms remain to be elucidated [1] – [2] . After 3 days, unattached cells were removed; the MSC cultures were maintained in the growth medium for about 2 weeks and then subcultured with 0.25% trypsin/EDTA (Invitrogen). On the second passage, some of the cells were cryopreserved (MSC preparation), and the others plated for the preparation of SB623 cells. For this, MSCs were transfected with the pCI-neo expression plasmid encoding human Notch intracellular domain ( NICD ). The transfection was performed with Fugene 6 (Roche Diagnostics, Indianapolis, IN) according to the manufacturer’s protocol. On the next day, the medium was replaced with growth medium containing 100 µg/ml G418 (Invitrogen), and the selection continued for 7 days. All experiments described here were performed with MSCs and SB623 cells that were cryopreserved, then thawed, grown for 5–6 days to allow recovery, and plated for the experiments. ECM Preparation For the preparation of cell-produced ECM, either MSCs or SB623 cells were plated at 2.7×10 4 cells/cm 2 on 10-cm plates (Nunc, Denmark), in growth medium. After 5 days, the growth medium was changed to serum-free medium, and the cells were cultured for an additional 2 days. The ECM Optimizing an in vitro method for decellularization of SB623 cell- and MSC-derived ECM involved many considerations. Methods using Triton and NH 4 OH dissolve cell/nuclear membranes yielding an intact ECM but allow for intracellular impurities. Cation chelating agents have been reported by other groups to remove monolayers of MSC [27] , but from our observations SB623 and MSCs do not fully detach under the same conditions. For this reason the use of Triton and NH 4 OH were used for decellularization, despite that this treatment results in many Triton-soluble intracellular/nuclear proteins that contaminate the ECM (see Table S1 ). Of the 22 proteins of interest, five have been reported to promote neuroregeneration: TNC, HSPG2, thrombospondin-1 (TSP1), FN1, and growth and differentiation factor-15 (GDF-15). Rigato et al. (2002) [34] have shown TNC to promote neurite outgrowth modulated through its fibronectin type III BD domains. TNC has been also been implicated in hippocampal-based learning and synaptic plasticity [35] . Yu et al. (2011) [36] showed TNC involvement in locomotor recovery after spinal cord injury. HSPG2 has been described by Lee et al. (2010) [37] to be pro-angiogenic and neuroprotective after ischemic stroke in rats. Future comparison across multiple donors will reveal whether these trends are typical of SB623. Fibrillin-1, LTBP-1, FN1, and transglutaminase 2 (TGM2) were significantly up-regulated, and fibulin-1 was down-regulated in SB623-derived ECM compared to MSC-derived ECM. These five proteins have been shown to play an interesting and important role in latent TGFβ localization in the ECM. TGFβ has been shown to be neuroprotective in the central nervous system and is induced after ischemic stroke [46] – [48] . Schwann cells promote synaptogenesis via TGF-β1 in the neuromuscular junction [49] .