Samenvatting
The cystine/glutamate antiporter, system xc-, is mainly expressed in the brain and on immune cells, and has been identified as a promising therapeutic target to treat neurological disorders and cancer. High expression of system xc- is beneficial for tumor cells mainly through the generation of the antioxidant glutathione, that is sustained by the cystine imported via the antiporter. Accordingly, targeting xCT (i.e. the specific subunit of the antiporter) not only reduces tumor growth but also decreases therapy resistance and metastasis. Furthermore, the involvement of system xc- in neurological disorders is mainly related to its contribution to the extracellular pool of glutamate -with (potential) implication in excitotoxicity- and its modulatory effect on neuroinflammation. Indeed, mice lacking xCT (xCT-/- mice) show a strong reduction in extracellular glutamate levels as well as attenuated (neuro)inflammation and depressive-like behavior following a peripheral injection of lipopolysaccharide (LPS).
To develop an effective therapeutic strategy to target system xc-, it is essential to understand the specific function of xCT in the brain and on peripheral immune cells, in pathological contexts. While a lot is known about the role of system xc- in the brain, the specific contribution of immune cell xCT in diseases has been understudied in vivo. We hypothesized that the beneficial effects of targeting system xc- on (neuro)inflammation originate in the immune system, and we therefore generated chimeras, lacking or not xCT on their immune cells. To test our hypothesis, we explored the role of xCT on immune cells in two different pathological conditions characterized by (neuro)inflammation, where absence of xCT is known to be protective: a mouse model of severe inflammation induced by a peripheral injection of LPS and a mouse model of pancreatic cancer.
We first developed a mouse model that would allow us to study the function of xCT specifically on immune cells. To do so, we generated bone marrow (BM) chimeras using irradiation and bone marrow transplantation (BMT). We tested different radiation strategies, including several doses, split or not, and with or without inclusion of the head of the mouse in the irradiation field. As total body irradiation appeared to be required to obtain sufficient replacement of the immune system, we investigated the impact of this protocol on the brain and behavior of the transplanted mice after 2 and 16 months. While irradiation did not impact the survival of the mice, it did result in a persistent delay in weight gain, impaired spontaneous locomotion, changes in the number and the morphology of cortical microglia as well as infiltration of donor-derived BM cells in the brain of transplanted mice. We did, however, not observe BMT-induced mood disturbances.
Next, we used this BMT model to investigate whether the protective effects that were previously observed in xCT-/- mice on LPS-induced (neuro)inflammation, sickness and depressive-like behavior could be replicated by targeting xCT only on immune cells. We found that 24h after LPS injection only mice lacking xCT on their immune cells recovered from LPS-induced hypothermia and they exhibited attenuated microglial activation in the hippocampus one week post-injection. Yet, only targeting xCT on peripheral immune cells was not sufficient to achieve the same level of protection against LPS-induced (neuro)inflammation as observed in congenital xCT-/- mice.
We next used the BMT model to study the involvement of immune cell xCT in pancreatic ductal adenocarcinoma (PDAC) -the most common type of pancreatic cancer- and its related comorbidities such as cachexia and mood disturbances, that are linked to (neuro)inflammation. Contrary to our observations in congenital xCT-/- mice, tumor burden as well as cancer-induced peripheral inflammation were similar between the xCT chimeras. However, absence of immune cell xCT prevented the cancer-induced increase in regulatory T cells, that are crucial immunosuppressive cells in PDAC, therefore suggesting an important function of immune cell xCT in supporting
regulatory T cell proliferation. Furthermore, targeting xCT on immune cells did not improve cachexia features, although there were some indications of attenuated cachexia-related lethargy in xCT-/- BM mice. Moreover, cancer-induced depressive-like behavior was reduced in mice lacking xCT on their immune cells. Our findings along with the results obtained using xCT-/- mice and xCT-deficient pancreatic tumor cells, provided valuable insights into the involvement of xCT in PDAC progression, cancer-induced cachexia and mood disturbances. We thus initiated a more translational study that combined sulfasalazine (SAS, a system xc- inhibitor) and gemcitabine (GEM, the standard
chemotherapeutic treatment for PDAC), to reduce tumor growth and cancer-related comorbidities in our PDAC mouse model. Although we evaluated different treatment strategies, the different doses of GEM we tested were extremely potent to reduce tumor growth, precluding definitive conclusions on the potential added value of SAS to treat PDAC and its comorbidities.
To conclude, we had to refute the hypothesis on which was based this doctoral dissertation, as targeting xCT only on immune cells was proven insufficient to provide protection against LPS- and cancer-induced (neuro)inflammation. Our data therefore support a role for xCT in other tissues, such as the brain or the adipose tissue, in modulating the (neuro)inflammatory responses.
To develop an effective therapeutic strategy to target system xc-, it is essential to understand the specific function of xCT in the brain and on peripheral immune cells, in pathological contexts. While a lot is known about the role of system xc- in the brain, the specific contribution of immune cell xCT in diseases has been understudied in vivo. We hypothesized that the beneficial effects of targeting system xc- on (neuro)inflammation originate in the immune system, and we therefore generated chimeras, lacking or not xCT on their immune cells. To test our hypothesis, we explored the role of xCT on immune cells in two different pathological conditions characterized by (neuro)inflammation, where absence of xCT is known to be protective: a mouse model of severe inflammation induced by a peripheral injection of LPS and a mouse model of pancreatic cancer.
We first developed a mouse model that would allow us to study the function of xCT specifically on immune cells. To do so, we generated bone marrow (BM) chimeras using irradiation and bone marrow transplantation (BMT). We tested different radiation strategies, including several doses, split or not, and with or without inclusion of the head of the mouse in the irradiation field. As total body irradiation appeared to be required to obtain sufficient replacement of the immune system, we investigated the impact of this protocol on the brain and behavior of the transplanted mice after 2 and 16 months. While irradiation did not impact the survival of the mice, it did result in a persistent delay in weight gain, impaired spontaneous locomotion, changes in the number and the morphology of cortical microglia as well as infiltration of donor-derived BM cells in the brain of transplanted mice. We did, however, not observe BMT-induced mood disturbances.
Next, we used this BMT model to investigate whether the protective effects that were previously observed in xCT-/- mice on LPS-induced (neuro)inflammation, sickness and depressive-like behavior could be replicated by targeting xCT only on immune cells. We found that 24h after LPS injection only mice lacking xCT on their immune cells recovered from LPS-induced hypothermia and they exhibited attenuated microglial activation in the hippocampus one week post-injection. Yet, only targeting xCT on peripheral immune cells was not sufficient to achieve the same level of protection against LPS-induced (neuro)inflammation as observed in congenital xCT-/- mice.
We next used the BMT model to study the involvement of immune cell xCT in pancreatic ductal adenocarcinoma (PDAC) -the most common type of pancreatic cancer- and its related comorbidities such as cachexia and mood disturbances, that are linked to (neuro)inflammation. Contrary to our observations in congenital xCT-/- mice, tumor burden as well as cancer-induced peripheral inflammation were similar between the xCT chimeras. However, absence of immune cell xCT prevented the cancer-induced increase in regulatory T cells, that are crucial immunosuppressive cells in PDAC, therefore suggesting an important function of immune cell xCT in supporting
regulatory T cell proliferation. Furthermore, targeting xCT on immune cells did not improve cachexia features, although there were some indications of attenuated cachexia-related lethargy in xCT-/- BM mice. Moreover, cancer-induced depressive-like behavior was reduced in mice lacking xCT on their immune cells. Our findings along with the results obtained using xCT-/- mice and xCT-deficient pancreatic tumor cells, provided valuable insights into the involvement of xCT in PDAC progression, cancer-induced cachexia and mood disturbances. We thus initiated a more translational study that combined sulfasalazine (SAS, a system xc- inhibitor) and gemcitabine (GEM, the standard
chemotherapeutic treatment for PDAC), to reduce tumor growth and cancer-related comorbidities in our PDAC mouse model. Although we evaluated different treatment strategies, the different doses of GEM we tested were extremely potent to reduce tumor growth, precluding definitive conclusions on the potential added value of SAS to treat PDAC and its comorbidities.
To conclude, we had to refute the hypothesis on which was based this doctoral dissertation, as targeting xCT only on immune cells was proven insufficient to provide protection against LPS- and cancer-induced (neuro)inflammation. Our data therefore support a role for xCT in other tissues, such as the brain or the adipose tissue, in modulating the (neuro)inflammatory responses.
| Originele taal-2 | English |
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| Toekennende instantie |
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| Begeleider(s)/adviseur |
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| Status | Published - 2024 |