Bioluminescence analysis of Smad-dependent TGF-beta signaling in live mice

TGF-β as a Key Modulator of Astrocyte Reactivity: Disease Relevance and Therapeutic Implications

Astrocytes are essential for normal brain development and functioning. They respond to brain injury and disease through a process referred to as reactive astrogliosis, where the reactivity is highly heterogenous and context-dependent. Reactive astrocytes are active contributors to brain pathology and can exert beneficial, detrimental, or mixed effects following brain insults. Transforming growth factor-β (TGF-β) has been identified as one of the key factors regulating astrocyte reactivity. The genetic and pharmacological manipulation of the TGF-β signaling pathway in animal models of central nervous system (CNS) injury and disease alters pathological and functional outcomes. This review aims to provide recent understanding regarding astrocyte reactivity and TGF-β signaling in brain injury, aging, and neurodegeneration. Further, it explores how TGF-β signaling modulates astrocyte reactivity and function in the context of CNS disease and injury.

A novel approach for monitoring TGF-β signaling in vivo in colon cancer

The TGF-β receptor kinase inhibitors (TRKI) have been reported to inhibit tumorigenicity in colon cancer. However, there is no direct evidence showing that these inhibitors function through inhibiting the TGF-β- mediated tumor-promoting effects in vivo. We established a TGF-β inducible reporter system by inserting a luciferase reporter gene to the vector downstream of TGF-β-inducible promoter elements, and transfected it into colon cancer cell lines. TRKIs SB431542 and LY2109761 were used to treat TGF-β inducible cells in vitro and in vivo. The luciferase activity was induced 5.24-fold by TGF-β in CT26 inducible cells, while it was marginally changed in MC38 inducible cells lacking Smad4 expression. Temporary treatment of mice with SB431542 inhibited the TGF-β pathway and TGF-β induced bioluminescence activity in vivo. Long-term treatment with LY2109761 inhibited tumorigenicity and liver metastasis in vivo in concomitant with reduced luciferase activity in the tumor. In this study, we established a model to monitor the TGF-β pathway in vivo and to compare the antitumor effects of TRKIs. Based on this novel experimental tool, we provided direct evidences that LY2109761 inhibits tumorigenicity and liver metastasis by blocking the pro-oncogenic functions of TGF-β in vivo.

Recombinant Pregnancy-Specific Glycoprotein 1 Has a Protective Role in a Murine Model of Acute Graft-versus-Host Disease

Acute graft-versus-host disease (aGVHD) is an immune-mediated reaction that can occur after hematopoietic stem cell transplantation in which donor T cells recognize the host antigens as foreign, destroying host tissues. Establishment of a tolerogenic immune environment while preserving the immune response to infectious agents is required for successful bone marrow transplantation. Pregnancy-specific glycoprotein 1 (PSG1), which is secreted by the human placenta into the maternal circulation throughout pregnancy, likely plays a role in maintaining immunotolerance to prevent rejection of the fetus by the maternal immune system. We have previously shown that PSG1 activates the latent form of transforming growth factor β1 (TGF-β), a cytokine essential for the differentiation of tolerance-inducing CD4⁺FoxP3⁺ regulatory T cells (Tregs). Consistent with this observation, treatment of naïve murine T cells with PSG1 resulted in a significant increase in FoxP3⁺ cells that was blocked by a TGF-β receptor I inhibitor. We also show here that PSG1 can increase the availability of active TGF-β in vivo. As the role of CD4⁺FoxP3⁺ cells in the prevention of aGVHD is well established, we tested whether PSG1 has beneficial effects in a murine aGHVD transplantation model. PSG1-treated mice had reduced numbers of tissue-infiltrating inflammatory CD3⁺ T cells and had increased expression of FoxP3 in T cells compared with vehicle-treated mice. In addition, administration of PSG1 significantly inhibited aGVHD-associated weight loss and mortality. On the other hand, administration of PSG1 was less effective in managing aGVHD in the presence of an alloimmune reaction against a malignancy in a graft-versus-leukemia experimental model. Combined, this data strongly suggests that PSG1 could be a promising treatment option for patients with aGVHD following bone marrow transplantation for a nonmalignant condition, such as an autoimmune disorder or a genetic immunodeficiency.

TGF-beta signalling in the adult neurogenic niche promotes stem cell quiescence as well as generation of new neurons

Members of the transforming growth factor (TGF)-β family govern a wide range of mechanisms in brain development and in the adult, in particular neuronal/glial differentiation and survival, but also cell cycle regulation and neural stem cell maintenance. This clearly created some discrepancies in the field with some studies favouring neuronal differentiation/survival of progenitors and others favouring cell cycle exit and neural stem cell quiescence/maintenance. Here, we provide a unifying hypothesis claiming that through its regulation of neural progenitor cell (NPC) proliferation, TGF-β signalling might be responsible for (i) maintaining stem cells in a quiescent stage, and (ii) promoting survival of newly generated neurons and their functional differentiation. Therefore, we performed a detailed histological analysis of TGF-β1 signalling in the hippocampal neural stem cell niche of a transgenic mouse that was previously generated to express TGF-β1 under a tetracycline regulatable Ca-Calmodulin kinase promoter. We also analysed NPC proliferation, quiescence, neuronal survival and differentiation in relation to elevated levels of TGF-β1 in vitro and in vivo conditions. Finally, we performed a gene expression profiling to identify the targets of TGF-β1 signalling in adult NPCs. The results demonstrate that TGF-β1 promotes stem cell quiescence on one side, but also neuronal survival on the other side. Thus, considering the elevated levels of TGF-β1 in ageing and neurodegenerative diseases, TGF-β1 signalling presents a molecular target for future interventions in such conditions.

Making the brain glow: in vivo bioluminescence imaging to study neurodegeneration

Bioluminescence imaging (BLI) takes advantage of the light-emitting properties of luciferase enzymes, which produce light upon oxidizing a substrate (i.e., D-luciferin) in the presence of molecular oxygen and energy. Photons emitted from living tissues can be detected and quantified by a highly sensitive charge-coupled device camera, enabling the investigator to noninvasively analyze the dynamics of biomolecular reactions in a variety of living model organisms such as transgenic mice. BLI has been used extensively in cancer research, cell transplantation, and for monitoring of infectious diseases, but only recently experimental models have been designed to study processes and pathways in neurological disorders such as Alzheimer disease, Parkinson disease, or amyotrophic lateral sclerosis. In this review, we highlight recent applications of BLI in neuroscience, including transgene expression in the brain, longitudinal studies of neuroinflammatory responses to neurodegeneration and injury, and in vivo imaging studies of neurogenesis and mitochondrial toxicity. Finally, we highlight some new developments of BLI compounds and luciferase substrates with promising potential for in vivo studies of neurological dysfunctions.

Molecular imaging of TGFβ-induced Smad2/3 phosphorylation reveals a role for receptor tyrosine kinases in modulating TGFβ signaling

PURPOSE

The dual modality of TGFβ, both as a potent tumor suppressor and a stimulator of tumor progression, invasion, and metastasis, make it a critical target for therapeutic intervention in human cancers. The ability to carry out real-time, noninvasive imaging of TGFβ-activated Smad signaling in live cells and animal models would significantly improve our understanding of the regulation of this unique signaling cascade. To advance these efforts, we developed a highly sensitive molecular imaging tool that repetitively, noninvasively, and dynamically reports on TGFBR1 kinase activity.

EXPERIMENTAL DESIGN

The bioluminescent TGFβR1 reporter construct was developed using a split firefly luciferase gene containing a functional sensor of Smad2 phosphorylation, wherein inhibition of TGFβ receptor1 kinase activity leads to an increase in reporter signaling. The reporter was stably transfected into mammalian cells and used to image in vivo and in vitro bioluminescent activity as a surrogate for monitoring TGFBR1 kinase activity.

RESULTS

The reporter was successfully used to monitor direct and indirect inhibition of TGFβ-induced Smad2 and SMAD3 phosphorylation in live cells and tumor xenografts and adapted for high-throughput screening, to identify a role for receptor tyrosine kinase inhibitors as modulators of TGFβ signaling.

CONCLUSION

The reporter is a dynamic, noninvasive imaging modality for monitoring TGFβ-induced Smad2 signaling in live cells and tumor xenografts. It has immense potential for identifying novel effectors of R-Smad phosphorylation, for validating drug-target interaction, and for studying TGFβ signaling in different metastasis models.