Abstract PO-115: Effects of mesothelin exert on tumor microenvironment in pancreatic ductal adenocarcinoma

Background: High mesothelin (MSLN) expression has been associated with poor prognosis in patients with pancreatic ductal adenocarcinoma (PDAC); however, the effect of MSLN exert on PDAC tumor microenvironment (TME) is largely unknown. Methods: MSLN over-expressed (MSLN-OE) and knocked-down (MSLN-KD) PDAC cells were established to investigate the MSLN-PD-L1 relationship in PDAC. Using an MSLN overexpressed Panc02 (Panc02-MSLN) cell line, we established an orthotopic PDAC mouse model. All mice were euthanized on day 27 after cell inoculation and the tumor-infiltrating leukocytes (TILs) were isolated for mass cytometry (CyTOF) study. The gene expression correlation between MSLN and a panel of immune cell markers was assessed by using a dataset that includes149 PDAC patients in the TCGA-PAAD cohort. Results: MSLN upregulated PD-L1 expression at both mRNA and protein levels in PDAC. MSLN was able to enhance PD-L1 transcription by recruitment of NF-kB P65 to the PD-L1 promoter. The Orthotopic implanted Panc02-MSLN group showed significantly increased tumor size, tumor weight, upregulated PD-L1, and reduced survival when compared with the vector control group. CyTOF analysis of the total CD45+ hematopoietic cells infiltrated to the TME revealed 13 distinct cell subsets. In MSLN-high tumors, there is a significant expansion of neutrophils, eosinophils, PD-1+CD8+, and CD8+NK cells. In addition, pan T cells, regulatory T cells (Treg), CD8+, and PD-1+CD4+ cells were increased. A considerable decrease of tumor-associated macrophages (TAM), dendritic cells, B cells, NK cells, and a trend towards decreased Ly6C+CD8+ cells was also found. Within the TAM subset, a decreased iNOS+M1 to Relm-a+M2 ratio was detected. Furthermore, although there were increased CD8+NK cells, we found more immunosuppressive markers such as PD-1, CTLA4, LAG3, KLRG1, and TIM3, and a decreased activation marker CD69 and transcription factor T-bet. Intriguingly, gene expression correlation analysis with 149 PDAC patients cohort in TCGA dataset showed that MSLN expression negatively correlates with the mRNA levels of the B220 marker of B cells, the F4/80 marker of macrophages, as well as the CD4, CD8, CD69, granzyme B, IL-2 and IFN-γ markers of T-cell activation. Conclusions: We showed here that MSLN could significantly modulate the TME, possibly through the upregulation of PD-L1 expression. Compared with MSLN-low PDAC tumors, MSLN-high tumors recruit diverse immunosuppressive rather than immunoreactive leukocytes into tumor tissues to constitute an immunologically cold TME. Since targeting MSLN or PD-L1 as a monotherapy exhibited only modest objective response rates in the clinic, our findings may provide an alternative strategy by combining the depletion of MSLN with immune checkpoint inhibitors, which could result in improved treatment efficacy in PDAC.

Citation Format: Dongliang Liu, Ethan Poteet, Zhengdong Liang, Emily Laplante, Lisa Brubaker, Sadhna Dhingra, Aleksandar Milosavljevic, Changyi Chen, Qizhi Cathy Yao. Effects of mesothelin exert on tumor microenvironment in pancreatic ductal adenocarcinoma [abstract]. In: Proceedings of the AACR Virtual Special Conference on Pancreatic Cancer; 2021 Sep 29-30. Philadelphia (PA): AACR; Cancer Res 2021;81(22 Suppl):Abstract nr PO-115.

Mesothelin and TGF-α predict pancreatic cancer cell sensitivity to EGFR inhibitors and effective combination treatment with trametinib

Clinical trials of EGFR inhibitors in combination with gemcitabine for the treatment of pancreatic ductal adenocarcinoma (PDAC) have generated mixed results partially due to the poorly defined effectiveness of EGFR inhibitors in PDAC. Here, we studied a panel of PDAC cell lines to compare the IC50s of the EGFR inhibitors gefitinib and cetuximab. We found that gefitinib induced biphasic inhibition in over 50% of PDAC cells, with the initial growth inhibition occurring at nanomolar concentrations and a second growth inhibition occurring outside the clinical range. In contrast to gefitinib, cetuximab produced a single phase growth inhibition in a subset of PDAC cells. Using this sensitivity data, we screened for correlations between cell morphology proteins and EGFR ligands to EGFR inhibitor sensitivity, and found that mesothelin and the EGFR ligand TGF-α have a strong correlation to gefitinib and cetuximab sensitivity. Analysis of downstream signaling pathways indicated that plc-γ1 and c-myc were consistently inhibited by EGFR inhibitor treatment in sensitive cell lines. While an inconsistent additive effect was observed with either cetuximab or gefitinib in combination with gemcitabine, the cell pathway data indicated consistent ERK activation, leading us to pursue EGFR inhibitors in combination with trametinib, a MEK1/2 inhibitor. Both cetuximab and gefitinib in combination with trametinib produced an additive effect in all EGFR sensitive cell lines. Our results indicate that mesothelin and TGF-α can predict PDAC sensitivity to EGFR inhibitors and a combination of EGFR inhibitors with trametinib could be a novel effective treatment for PDAC.

Overexpression of Semaphorin-3E enhances pancreatic cancer cell growth and associates with poor patient survival

Semaphorin-3E (Sema3E) is a member of an axon guidance gene family, and has recently been reported to contribute to tumor progression and metastasis. However, its role in pancreatic cancer is yet unknown and uncharacterized. In this study, we showed that Sema3E is overexpressed in human pancreatic cancer, and that high Sema3E levels are associated with tumor progression and poor survival. Interestingly, we also observed Sema3E expression in the nucleus, even though Sema3E is reported to be a secreted protein. Overexpression of Sema3E in pancreatic cancer cells promoted cell proliferation and migration in vitro, and increased tumor incidence and growth in vivo. Conversely, knockout of Sema3E suppressed cancer cell proliferation and migration in vitro, and reduced tumor incidence and size in vivo. Moreover, Sema3E induced cell proliferation via acting through the MAPK/ERK pathway. Collectively, these results reveal an undiscovered role of Sema3E in promoting pancreatic cancer pathogenesis, suggesting that Sema3E may be a suitable prognostic marker and therapeutic target for pancreatic cancer.

Toll-like receptor 3 adjuvant in combination with virus-like particles elicit a humoral response against HIV

Human Immunodeficiency Virus (HIV) Virus-Like Particles (VLPs) composed of HIV_IIIB Gag and HIV_BaL gp120/gp41 envelope are a pseudovirion vaccine capable of presenting antigens in their native conformations. To enhance the immunogenicity of the HIV Env antigen, VLPs were coupled to VesiVax Conjugatable Adjuvant Lipid Vesicles (CALV) containing one of four toll-like-receptor (TLR) ligands, each activating a receptor with distinct cellular localization and downstream pathways. C57BL/6 mice were vaccinated by intranasal prime followed by two sub-cheek boosts and their sera immunoglobulin and neutralizing potency were measured over a duration of 3months after vaccination. PBS control, VLPs alone, CALV+VLPs, and VLPs complexed with CALV and ligands for TLR2 (PAM3CAG), TLR3 (dsRNA), TLR4 (MPLA), or TLR7/8 (resiquimod) were evaluated based on antibody titer, IgG1 and IgG2c class switching, germinal center formation, T follicular cells and potency of neutralizing antibodies. Consistently, the TLR3 ligand dsRNA complexed to CALV and in combination with VLPs (CALV(dsRNA)+VLPs) induced the strongest response. CALV(dsRNA)+VLPs induced the highest titers against the recombinant vaccine antigens clade B Bal gp120 and pr55 Gag. Additionally, CALV(dsRNA)+VLPs induced cross-clade antibodies, represented by high titers of antibody to clade c 96ZM651 gp120. CALV(dsRNA)+VLPs induced predominantly IgG2c over IgG1, a response associated with T helper type 1 (Th1)-like cytokines. In turn, CALV(dsRNA)+VLP immunized mice generated the most potent neutralizing antibodies against HIV strain MN.3. Finally, at time of sacrifice, a significant increase in germinal center B cells and T follicular cells was detected in mice which received CALV(dsRNA)+VLPs compared to PBS. Our results indicate that CALV(dsRNA) is a superior adjuvant for HIV VLPs in generating a Th1-like immunoglobulin profile, while prolonging lymph node germinal centers, T follicular cells and generating neutralizing antibodies to a highly sensitive tier 1A variant of HIV.

Abstract A48: Overexpression of Semaphorin-3E enhances pancreatic cancer cell proliferation ad is associated with patient poor survival

Background: Pancreatic ductal adenocarcinoma (PDAC) is the 4th leading cause of cancer death in the US with a 5-year survival rate of less than 6%. There is an urgent need for a better understanding of PDAC in order to find better therapeutic targets. Two recent large-scale genomic analyses of human PDAC have uncovered increased copy numbers of an axon-guidance gene SEMA3E that codes for Semaphorin-3E (Sema3E). Several recent reports have implicated Sema3E in metastasis of breast and colon cancers, particularly in promoting tumor cell migration and invasion, as well as inducing epithelial-to-mesenchymal transition (EMT). Here, we evaluated Sema3E expression levels in human pancreatic cancer tissue samples and correlation with patient survival; we further studied roles of Sema3E in pancreatic cancer cell proliferation.

Materials and Methods: To determine expression levels of Sema3E in PDAC, qPCR analysis was performed on resected human PDAC samples and matched tissue controls, and immunohistochemical (IHC) analysis was performed on resected human PDAC tissues and tissues from a mouse model of PDAC. To generate Sema3E-overexpressing stable cells, human PDAC cell lines were transduced with Sema3E-expressing lentivirus or vector control. To generate Sema3E knock-down cell lines, CRISPR/Cas9 system was used to target Sema3E in the genome. MTT assay was performed on Sema3E-overexpressed cells to determine the effects of Sema3E on cell proliferation.

Results: Using qPCR, Sema3E was found to be significantly upregulated in 46% of human PDAC samples (n=24), with an average fold-change of 9.54. IHC analyses of human and mouse PDAC revealed higher expression of Sema3E in tumor cells compared to normal cells (n=54). Interestingly, in human PDAC, Sema3E expression was concentrated in the nuclei of tumor cells while it has been reported to be a secreted protein. We found a positive correlation between high N/C ratio of Sema3E expression (i.e. expression in the nucleus relative to the cytoplasm) and poor survival. In addition, we also found overexpression of Sema3E is correlated with patient poor survival by analyzing a TCGA dataset (n=78). Overexpression of Sema3E in human PDAC cell lines enhanced cell proliferation and migration in vitro, while knocking-down Sema3E resulted in reduced cell proliferation.

Conclusions: Our findings indicate that Sema3E is overexpressed in PDAC and is correlated with patient poor survival. Sema3E may play a pathogenic role in PDAC progression by enhancing tumor cell proliferation. These findings suggest that Sema3E could be an attractive novel therapeutic target for PDAC.

Citation Format: Lin-Kin Yong, Syeling Lai, Zhengdong Liang, Dali Li, Ethan Poteet, William Fisher, Qianxin Mo, Changyi Chen, Qizhi Yao. Overexpression of Semaphorin-3E enhances pancreatic cancer cell proliferation ad is associated with patient poor survival. [abstract]. In: Proceedings of the Fourth AACR International Conference on Frontiers in Basic Cancer Research; 2015 Oct 23-26; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2016;76(3 Suppl):Abstract nr A48.

A Novel Prime and Boost Regimen of HIV Virus-Like Particles with TLR4 Adjuvant MPLA Induces Th1 Oriented Immune Responses against HIV

HIV virus-like particles (VLPs) present the HIV envelope protein in its native conformation, providing an ideal vaccine antigen. To enhance the immunogenicity of the VLP vaccine, we sought to improve upon two components; the route of administration and the additional adjuvant. Using HIV VLPs, we evaluated sub-cheek as a novel route of vaccine administration when combined with other conventional routes of immunization. Of five combinations of distinct prime and boost sequences, which included sub-cheek, intranasal, and intradermal routes of administration, intranasal prime and sub-cheek boost (IN+SC) resulted in the highest HIV-specific IgG titers among the groups tested. Using the IN+SC regimen we tested the adjuvant VesiVax Conjugatable Adjuvant Lipid Vesicles (CALV) + monophosphoryl lipid A (MPLA) at MPLA concentrations of 0, 7.5, 12.5, and 25 μg/dose in combination with our VLPs. Mice that received 12.5 or 25 μg/dose MPLA had the highest concentrations of Env-specific IgG2c (20.7 and 18.4 μg/ml respectively), which represents a Th1 type of immune response in C57BL/6 mice. This was in sharp contrast to mice which received 0 or 7.5 μg MPLA adjuvant (6.05 and 5.68 μg/ml of IgG2c respectively). In contrast to IgG2c, MPLA had minor effects on Env-specific IgG1; therefore, 12.5 and 25 μg/dose of MPLA induced the optimal IgG1/IgG2c ratio of 1.3. Additionally, the percentage of germinal center B cells increased significantly from 15.4% in the control group to 31.9% in the CALV + 25 μg MPLA group. These mice also had significantly more IL-2 and less IL-4 Env-specific CD8⁺ T cells than controls, correlating with an increased percentage of Env-specific central memory CD4⁺ and CD8⁺ T cells. Our study shows the strong potential of IN+SC as an efficacious route of administration and the effectiveness of VLPs combined with MPLA adjuvant to induce Env specific Th1-oriented HIV-specific immune responses.

Abstract 3574: Novel roles of an axon-guidance molecule, semaphorin 3E, in pancreatic cancer

Background:

Pancreatic ductal adenocarcinoma (PDAC) is the 4th leading cause of cancer death in the US with a 5-year survival rate of less than 6%. There is an urgent need for a better understanding of PDAC in order to find better therapeutic targets. Two recent large-scale genomic analyses of human PDAC have uncovered increased copy numbers of an axon-guidance gene SEMA3E that codes for Semaphorin-3E (Sema3E). Several recent reports have implicated Sema3E in metastasis of breast and colon cancers, particularly in promoting tumor cell migration and invasion, as well as inducing epithelial-to-mesenchymal transition (EMT). We hypothesize a possible new role of an axon-guidance gene Sema3E in PDAC progression by promoting cell proliferation, invasion, and metastasis.

Materials and Methods:

To determine expression levels of Sema3E in human PDAC, qRT-PCR and IHC analysis was performed on resected PDAC samples and matched tissue controls. To determine Sema3E levels in mouse PDAC, IHC analysis was performed on pancreas tissue from a genetically engineered spontaneous PDAC mouse model, the PDX-1-Cre; KrasG12D; P53R172H (KPC) mouse. To generate Sema3E-overexpressing stable cells, human PDAC cell lines Mia PaCa-2 and Panc-48 cells were transduced with Sema3E-expressing lentivirus or vector control. QRT-PCR and western blot analyses were performed to verify the overexpression of Sema3E. Colony formation assay (CFA) and MTT assay were performed on Sema3E-transduced cells to determine the effects of Sema3E on cell survival and proliferation respectively, while a wound healing assay and boyden chamber assay were performed to determine effects of Sema3E on cell migration and invasion respectively.

Results:

Sema3E was found to be significantly upregulated in 46% of patient PDAC samples (n = 24), with an average fold-change of 9.54 across the samples. IHC analyses of patient and mouse PDAC revealed higher expression of Sema3E in tumor cells compared to normal cells. Interestingly, Sema3E expression was concentrated in the nuclei of tumor cells while it has been reported in current literature to be a secreted protein found in normal tissues. Sema3E-transduced PDAC cell lines Mia PaCa-2-Sema3E and Panc-48-Sema3E had higher Sema3E expression in cell lysates and culture supernatant compared to control cells. Mia PaCa-2-Sema3E had a 60.4% higher rate of colony formation than the control (p = 0.005), while both Mia PaCa-2-Sema3E and Panc-48-Sema3E had higher proliferation rates (58.8%; p<0.0001 and 31.0%; p<0.0001 respectively) compared to controls. Interestingly, both Sema3E-transduced cells did not have a significant difference in migration and invasion compared to controls.

Conclusions:

Our findings indicate that Sema3E is overexpressed in PDAC and it may play some pathogenic roles in PDAC progression by enhancing tumor cell proliferation. These findings indicate that Sema3E could be an attractive novel therapeutic target in PDAC treatment strategies.

Citation Format: Lin-Kin Yong, Dali Li, Ethan Poteet, Zhengdong Liang, William Fisher, Changyi Chen, Qizhi Cathy Yao. Novel roles of an axon-guidance molecule, semaphorin 3E, in pancreatic cancer. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 3574. doi:10.1158/1538-7445.AM2015-3574

Cancer-associated isocitrate dehydrogenase 1 (IDH1) R132H mutation and d-2-hydroxyglutarate stimulate glutamine metabolism under hypoxia

Mutations in the cytosolic NADP(+)-dependent isocitrate dehydrogenase (IDH1) occur in several types of cancer, and altered cellular metabolism associated with IDH1 mutations presents unique therapeutic opportunities. By altering IDH1, these mutations target a critical step in reductive glutamine metabolism, the metabolic pathway that converts glutamine ultimately to acetyl-CoA for biosynthetic processes. While IDH1-mutated cells are sensitive to therapies that target glutamine metabolism, the effect of IDH1 mutations on reductive glutamine metabolism remains poorly understood. To explore this issue, we investigated the effect of a knock-in, single-codon IDH1-R132H mutation on the metabolism of the HCT116 colorectal adenocarcinoma cell line. Here we report the R132H-isobolome by using targeted (13)C isotopomer tracer fate analysis to trace the metabolic fate of glucose and glutamine in this system. We show that introduction of the R132H mutation into IDH1 up-regulates the contribution of glutamine to lipogenesis in hypoxia, but not in normoxia. Treatment of cells with a d-2-hydroxyglutarate (d-2HG) ester recapitulated these changes, indicating that the alterations observed in the knocked-in cells were mediated by d-2HG produced by the IDH1 mutant. These studies provide a dynamic mechanistic basis for metabolic alterations observed in IDH1-mutated tumors and uncover potential therapeutic targets in IDH1-mutated cancers.

In vitro protection by pyruvate against cadmium-induced cytotoxicity in hippocampal HT-22 cells

Cadmium is a toxic metal with no biological function in higher-order mammals. Humans are exposed to cadmium environmental contamination and the mechanism underlying the cadmium's cytotoxicity is unclear. To better understand this mechanism, we employed murine hippocampal HT-22 cells to test the in vitro effects of cadmium toxicity. Our study indicated that cadmium inhibits both mitochondria oxidative phosphorylation and glycolysis. In turn, this causes depolarization of mitochondrial membrane potential, increase of superoxide production and decrease of ATP generation. Furthermore, we demonstrated that the detrimental action of cadmium in bioenergetics could be mitigated by pyruvate, an intermediate metabolic product. Pyruvate decreased superoxide production, maintained mitochondrial membrane potential, restored glycolysis, mitigated the decrease in cellular ATP and attenuated cadmium cytotoxicity. Our study provides the first evidence that pyruvate might offer promising therapy for cadmium poisoning.

Reversing the Warburg effect as a treatment for glioblastoma

Glioblastoma multiforme (GBM), like most cancers, possesses a unique bioenergetic state of aerobic glycolysis known as the Warburg effect. Here, we documented that methylene blue (MB) reverses the Warburg effect evidenced by the increasing of oxygen consumption and reduction of lactate production in GBM cell lines. MB decreases GBM cell proliferation and halts the cell cycle in S phase. Through activation of AMP-activated protein kinase, MB inactivates downstream acetyl-CoA carboxylase and decreases cyclin expression. Structure-activity relationship analysis demonstrated that toluidine blue O, an MB derivative with similar bioenergetic actions, exerts similar action in GBM cell proliferation. In contrast, two other MB derivatives, 2-chlorophenothiazine and promethazine, exert no effect on cellular bioenergetics and do not inhibit GBM cell proliferation. MB inhibits cell proliferation in both temozolomide-sensitive and -insensitive GBM cell lines. In a human GBM xenograft model, a single daily dosage of MB does not activate AMP-activated protein kinase signaling, and no tumor regression was observed. In summary, the current study provides the first in vitro proof of concept that reversal of Warburg effect might be a novel therapy for GBM.

Involvement of estrogen receptor β5 in the progression of glioma

Emerging evidence suggests a decline of ERβ expression in various peripheral cancers. ERβ has been proposed as a cancer brake that inhibits tumor proliferation. In the current study, we have identified ERβ5 as the predominant isoform of ERβ in human glioma and its expression was significantly increased in human glioma as compared with non-neoplastic brain tissue. Hypoxia and activation of hypoxia inducible factor (HIF) increased ERβ transcription in U87 cells, suggesting elevated ERβ expression in glioma might be induced by the hypoxic stress in the tumor. Over-expression of either ERβ1 or ERβ5 increased PTEN expression and inhibited activation of the PI3K/AKT/mTOR pathway. In addition, ERβ5 inhibited the MAPK/ERK pathway. In U87 cells, ERβ1 and ERβ5 inhibit cell proliferation and reduced cells in the S+G2/M phase. Our findings suggest hypoxia induced ERβ5 expression in glioma as a self-protective mechanism against tumor proliferation and that ERβ5 might serve as a therapeutic target for the treatment of glioma.

Neuroprotective actions of methylene blue and its derivatives

Methylene blue (MB), the first lead chemical structure of phenothiazine and other derivatives, is commonly used in diagnostic procedures and as a treatment for methemoglobinemia. We have previously demonstrated that MB could function as an alternative mitochondrial electron transfer carrier, enhance cellular oxygen consumption, and provide protection in vitro and in rodent models of Parkinson's disease and stroke. In the present study, we investigated the structure-activity relationships of MB in vitro using MB and six structurally related compounds. MB reduces mitochondrial superoxide production via alternative electron transfer that bypasses mitochondrial complexes I-III. MB mitigates reactive free radical production and provides neuroprotection in HT-22 cells against glutamate, IAA and rotenone toxicity. Distinctly, MB provides no protection against direct oxidative stress induced by glucose oxidase. Substitution of a side chain at MB's 10-nitrogen rendered a 1000-fold reduction of the protective potency against glutamate neurototoxicity. Compounds without side chains at positions 3 and 7, chlorophenothiazine and phenothiazine, have distinct redox potentials compared to MB and are incapable of enhancing mitochondrial electron transfer, while obtaining direct antioxidant actions against glutamate, IAA, and rotenone insults. Chlorophenothiazine exhibited direct antioxidant actions in mitochondria lysate assay compared to MB, which required reduction by NADH and mitochondria. MB increased complex IV expression and activity, while 2-chlorphenothiazine had no effect. Our study indicated that MB could attenuate superoxide production by functioning as an alternative mitochondrial electron transfer carrier and as a regenerable anti-oxidant in mitochondria.

Androgens exacerbate motor asymmetry in male rats with unilateral 6-hydroxydopamine lesion

Parkinson's disease (PD) is a progressive neurodegenerative disorder characterized by dopamine neuron loss in the nigrostriatal pathway that shows greater incidence in men than women. The mechanisms underlying this gender bias remain elusive, although one possibility is that androgens may increase dopamine neuronal vulnerability to oxidative stress. Motor impairment can be modeled in rats receiving a unilateral injection of 6-hydroxydopamine (6-OHDA), a neurotoxin producing nigrostriatal degeneration. To investigate the role of androgens in PD, we compared young (2 months) and aged (24 months) male rats receiving gonadectomy (GDX) and their corresponding intact controls. One month after GDX, rats were unilaterally injected with 6-OHDA, and their motor impairment and asymmetry were assessed 2 weeks later using the cylinder test and the amphetamine-induced rotation test. Plasma samples were also collected to assess the concentration of testosterone and advanced oxidation protein products, a product of oxidative stress. GDX decreased lesion-induced asymmetry along with oxidative stress and increased amphetamine-induced rotations. These results show that GDX improves motor behaviors by decreasing motor asymmetry in 6-OHDA-treated rats, an effect that may be ascribed to increased release of striatal dopamine and decreased oxidative stress. Collectively, the data support the hypothesis that androgens may underlie the gender bias observed in PD.

Regulation of matrix metalloproteinase 2 by oligomeric amyloid β protein

Matrix metalloproteinases (MMPs) are a group of proteinases that degrade components of the extracellular matrix (ECM). There is increasing evidence for a link between the activation of MMPs and Alzheimer's disease (AD) pathogenesis, in which both beneficial and detrimental actions of MMPs have been suggested. It has been demonstrated that MMPs could degrade amyloid β (Aβ) and play important roles in the extracellular Aβ catabolism and clearance. On the other hand, MMPs could contribute to AD pathogenesis by compromising the blood brain barrier and promoting neurodegeneration. In the present study, we observed that oligomeric Aβ regulates MMP2 expression in a paradoxical manner. In rat primary astrocyte cultures, oligomeric Aβ down-regulated MMP2 transcription and reduced its extracellular activity. However, in a widely used mouse model for AD, immunohistochemistry demonstrated an increase of MMP2 expression in astrocytes surrounding senile plaques in APP/PS1 transgenic mice brains. Using real-time PCR, we found that the MMP2 mRNA level was elevated in APP/PS1 transgenic mice brains. In addition, elevated mRNA levels of MMP stimulating cytokines such as IL-1β and TGFβ were found in the brains of APP/PS1 mice. Our study suggests a complex regulation of MMP2 expression by oligomeric Aβ in astrocytes. While oligomeric Aβ directly down-regulates MMP2 expression and activation in astrocytes, it induces production of proinflammatory cytokines which could serve as strong stimulators for MMP2. Therefore, the ultimate outcome of the oligomeric Aβ on MMP2 activation in astrocytes might be the combination of its direct inhibitory action on astrocyte MMP2 expression and the secondary action of inducing inflammatory cytokines.

Towards a quantitative representation of the cell signaling mechanisms of hallucinogens: measurement and mathematical modeling of 5-HT1A and 5-HT2A receptor-mediated ERK1/2 activation

Through a multidisciplinary approach involving experimental and computational studies, we address quantitative aspects of signaling mechanisms triggered in the cell by the receptor targets of hallucinogenic drugs, the serotonin 5-HT2A receptors. To reveal the properties of the signaling pathways, and the way in which responses elicited through these receptors alone and in combination with other serotonin receptors' subtypes (the 5-HT1AR), we developed a detailed mathematical model of receptor-mediated ERK1/2 activation in cells expressing the 5-HT1A and 5-HT2A subtypes individually, and together. In parallel, we measured experimentally the activation of ERK1/2 by the action of selective agonists on these receptors expressed in HEK293 cells. We show here that the 5-HT1AR agonist Xaliproden HCl elicited transient activation of ERK1/2 by phosphorylation, whereas 5-HT2AR activation by TCB-2 led to higher, and more sustained responses. The 5-HT2AR response dominated the MAPK signaling pathway when co-expressed with 5-HT1AR, and diminution of the response by the 5-HT2AR antagonist Ketanserin could not be rescued by the 5-HT1AR agonist. Computational simulations produced qualitative results in good agreement with these experimental data, and parameter optimization made this agreement quantitative. In silico simulation experiments suggest that the deletion of the positive regulators PKC in the 5-HT2AR pathway, or PLA2 in the combined 5-HT1A/2AR model greatly decreased the basal level of active ERK1/2. Deletion of negative regulators of MKP and PP2A in 5-HT1AR and 5-HT2AR models was found to have even stronger effects. Under various parameter sets, simulation results implied that the extent of constitutive activity in a particular tissue and the specific drug efficacy properties may determine the distinct dynamics of the 5-HT receptor-mediated ERK1/2 activation pathways. Thus, the mathematical models are useful exploratory tools in the ongoing efforts to establish a mechanistic understanding and an experimentally testable representation of hallucinogen-specific signaling in the cellular machinery, and can be refined with quantitative, function-related information.