inducing-characterizing-vesicular-steatosis-differentiated-heparg

Inducing and Characterizing Vesicular Steatosis in Differentiated HepaRG Cells

Hepatic steatosis represents a metabolic dysfunction that results from an accumulation of triglyceride-containing lipid droplets in hepatocytes. Excessive ...

sapienza university

Pasteur Institute Italy-Fondazione Cenci Bolognetti

Regulatory T cells (Treg) exert a dominant role in the protection of unwanted immune responses and in the resolution of inflammation. To ensure the proper mounting of protective immune responses, Treg should be finely modulated by microenvironmental signals, mostly conveyed by cytokines. Type-I interferons are pleiotropic cytokines, best known for their anti-viral activities but also playing relevant immunostimulatory as well as immunomodulatory functions. The impact of type-I interferons on Treg homeostasis and functions is quite controversial, as some studies indicate that interferons sustain Treg stability and suppression, while other reports describe a null or even negative role for interferons in Treg activities. Interferons may also establish alternative routes of suppression, through the induction of other suppressive populations, such as Tr1 and the recently discovered FoxA1+ Treg. Discrepant results about Treg behavior in vivo emerge also from data collected in patients with multiple sclerosis, chronic hepatitis C or cancer undergoing interferon therapy. Concurrent events, such as Treg-extrinsic interferon activities, desensitization to chronic interferon exposure, and changes in microenvironmental signals during the evolution of diseases, may contribute to depict such a complex scenario, in which short-term and long-term effects of interferon exposure may give rise to apparently opposite conclusions. 

Divergent effects of type-I interferons on regulatory T cells.

Regulatory T cells (Tregs) encompass an array of immunosuppressive cells responsible for the protection against exacerbated immune responses and the maintenance of tissue homeostasis. Various Treg subtypes, normally resident within distinct lymphoid and non-lymphoid tissues, can be recruited and expanded during inflammation, possibly undergoing functional and molecular re-programming. Generally, two processes have been reported in different settings of type-1 response: i) Treg subpopulations acquiring the ability to specifically suppress Th1 cells (called Th1-suppressing Tregs), and ii) Treg subsets rather polarizing into IFN-γ-producing (called Th1-like) Tregs.Along the development of type-1 responses, Tregs are exposed to a variety of cytokines and other signals, exerting disparate activities. The combinatorial effects of typical Th1-driving cytokines, such as IL-12 (mostly produced by antigen-presenting cells during Th1 priming) and IFN-γ (mostly produced by pre-existing NK cells) lead to inhibition of Treg expansion and function, while promoting Th1-like Treg polarization. Conversely, cytokines produced at more advanced phases by Th1 effectors, such as IL-2, TNF-α and IFN-γ, promote Treg proliferation and/or Th1-suppressing Treg specialization. Some controversy exists around IL-27 and IFN-α, cytokines possibly released during bacterial or viral infections. Furthermore, cytokine signals can be finely tuned by the concomitant stimulation of costimulatory or coinhibitory receptors, such as OX40 and PD-1 respectively, within inflamed tissues.A model may be envisaged of an alternate Treg response to type-1 cytokines, being hampered or boosted by early or late phase cytokines, respectively. Such regulation would unleash the development of protective type-1 immunity while constraining exacerbated Th1 responses, possibly causing immunopathology. 

Stability of Regulatory T Cells Undermined or Endorsed by Different Type-1 Cytokines.

Type I IFNs are pleiotropic cytokines that exert concerted activities in the development of antiviral responses. Regulatory T cells represent a physiologic checkpoint in the balance between immunity and tolerance, requiring fine and rapid controls. Here, we show that human regulatory T cells are particularly sensitive to the sequential effects of IFN-α. First, IFN-α exerts a rapid, antiproliferative and proapoptotic effect in vitro and in vivo, as early as after 2 d of pegylated IFN/ribavirin therapy in patients with chronic hepatitis C. Such activities result in the decline, at d 2, in circulating regulatory T cell frequency and specifically of the activated regulatory T cell subset. Later, IFN-based therapy restrains the fraction of regulatory T cells that can be polarized into IFN-γ-producing Th1-like regulatory T cells known to contribute to chronic immune activation in type 1 inflammation. Indeed, Th1-like regulatory T cell frequency significantly declines after 30 d of therapy in vivo in relation to the persistent decline of relevant IL-12 sources, namely, myeloid and 6-sulfo LacNAc-expressing dendritic cells. This event is recapitulated by experiments in vitro, providing evidence that it may be attributable to the inhibitory effect of IFN-α on IL-12-induced, Th1-like regulatory T cell polarization. In summary, our results suggest that IFN-α-driven, early regulatory T cell depletion contributes to the development of antiviral immunity, ultimately resulting in the resolution of type 1 inflammation.

IFN-α promotes rapid human Treg contraction and late Th1-like Treg decrease.

The tumor microenvironment restrains conventional T cell (Tconv) activation while facilitating the expansion of Tregs. Here we showed that Tregs' advantage in the tumor milieu relies on supplemental energetic routes involving lipid metabolism. In murine models, tumor-infiltrating Tregs displayed intracellular lipid accumulation, which was attributable to an increased rate of fatty acid (FA) synthesis. Since the relative advantage in glucose uptake may fuel FA synthesis in intratumoral Tregs, we demonstrated that both glycolytic and oxidative metabolism contribute to Tregs' expansion. We corroborated our data in human tumors showing that Tregs displayed a gene signature oriented toward glycolysis and lipid synthesis. Our data support a model in which signals from the tumor microenvironment induce a circuitry of glycolysis, FA synthesis, and oxidation that confers a preferential proliferative advantage to Tregs, whose targeting might represent a strategy for cancer treatment.

Fatty acid metabolism complements glycolysis in the selective regulatory T cell expansion during tumor growth.

Non-alcoholic fatty liver disease (NAFLD) is a leading cause of chronic liver disease. Although genetic predisposition and epigenetic factors contribute to the development of NAFLD, our understanding of the molecular mechanism involved in the pathogenesis of the disease is still emerging. Here we investigated a possible role of a microRNAs-STAT3 pathway in the induction of hepatic steatosis. Differentiated HepaRG cells treated with the fatty acid sodium oleate (fatty dHepaRG) recapitulated features of liver vesicular steatosis and activated a cell-autonomous inflammatory response, inducing STAT3-Tyrosine-phosphorylation. With a genome-wide approach (Chromatin Immunoprecipitation Sequencing), many phospho-STAT3 binding sites were identified in fatty dHepaRG cells and several STAT3 and/or NAFLD-regulated microRNAs showed increased expression levels, including miR-21. Innovative CARS (Coherent Anti-Stokes Raman Scattering) microscopy revealed that chemical inhibition of STAT3 activity decreased lipid accumulation and deregulated STAT3-responsive microRNAs, including miR-21, in lipid overloaded dHepaRG cells. We were able to show in vivo that reducing phospho-STAT3-miR-21 levels in C57/BL6 mice liver, by long-term treatment with metformin, protected mice from aging-dependent hepatic vesicular steatosis. Our results identified a microRNAs-phosphoSTAT3 pathway involved in the development of hepatic steatosis, which may represent a molecular marker for both diagnosis and therapeutic targeting.

Targeting a phospho-STAT3-miRNAs pathway improves vesicular hepatic steatosis in an in vitro and in vivo model.

In the present review, we analyzed the various overlapping and non-mutually exclusive mechanisms that intersect and form complex and highly flexible immunological networks allowing the defense against liver infections and tumors. Liver immunity results from the combination of the skills of systemic and local immune system(s) to sense and recognize pathogen or tumor antigens, to sensitize a wide range of innate and adaptive immune cells, and to clear the "invaders", through the establishment of a transient liver immunopathology state undergoing resolution/control of infections or tumors, and memory development. Then, a special emphasis is placed on discussing about the capacity of the immune system(s) to develop a state of chronic low-level immunopathology adapting through the intervention of simultaneous immunoregulatory mechanisms, when the liver is infected by highly mutable viruses (e.g., hepatitis B or C viruses [HBV or HCV]) capable to escape from the immune recognition. The establishment of chronic inflammation represents an advantage for the species survival, because it guarantees the long-term survival of human hosts despite the virus persistence. However, chronic inflammation, in the long run, can evolve towards severe consequences (decompensated cirrhosis and hepatocellular carcinoma) in some individuals, finding requiring the impelling need of discovering new therapeutic anti-viral and immunostimulatory agents addressed, in combination, to fight especially HBV that, in contrast to HCV, lacks antivirals capable to eradicate the virus. Finally, we discussed the concept proposing that the divergent immunoregulatory mechanisms that develop in persisting infections or tumors, on the one hand, and autoimmunity, on the other hand, are the mirror image of each other, whose understanding is also relevant for preparing novel immunotherapeutic approaches in autoimmune diseases.

Viral hepatitis, inflammation, and cancer: A lesson for autoimmunity.

Mitochondria are key players in the regulation of T cell biology by dynamically responding to cell needs, but how these dynamics integrate in T cells is still poorly understood. We show here that the mitochondrial pro-fission protein Drp1 fosters migration and expansion of developing thymocytes both in vitro and in vivo. In addition, we find that Drp1 sustains in vitro clonal expansion and cMyc-dependent metabolic reprogramming upon activation, also regulating effector T cell numbers in vivo. Migration and extravasation defects are also exhibited in Drp1-deficient mature T cells, unveiling its crucial role in controlling both T cell recirculation in secondary lymphoid organs and accumulation at tumor sites. Moreover, the observed Drp1-dependent imbalance toward a memory-like phenotype favors T cell exhaustion in the tumor microenvironment. All of these findings support a crucial role for Drp1 in several processes during T cell development and in anti-tumor immune-surveillance.

Drp1 Controls Effective T Cell Immune-Surveillance by Regulating T Cell Migration, Proliferation, and cMyc-Dependent Metabolic Reprogramming.

Background Digoxin use was shown to be associated with an increased risk of cardiovascular events in atrial fibrillation ( AF ). We hypothesized that digoxin may affect cardiovascular risk by increasing platelet activation. Methods and Results Post hoc analysis of a prospective study of anticoagulated patients with AF . Patients were divided into 2 groups balanced for age, sex, and cardiovascular risk factors: digoxin users (n=132) and nonusers (n=388). Urinary excretion of 11-dehydro-thromboxane B (TxB), a marker of platelet activation, and serum digoxin concentration ( SDC ) were measured. In vitro experiments were performed on platelets from healthy subjects and AF patients, which were incubated with scalar doses of digoxin (0.6-2.4 ng/mL) with or without prestimulation with a sub-threshold of collagen. Median 11-dehydro-TxB was 105.0 ( interquartile range, 60.0-190.0) ng/mg creatinine, and median SDC was 0.65 ( interquartile range, 0.40-1.00) ng/mL. Urinary 11-dehydro-TxB and SDC were correlated ( r=0.350, P<0.001). Patients in the upper tertile of SDC showed higher 11-dehydro-TxB compared with non-digoxin users ( P=0.019). In vitro study showed an increased basal platelet activation in patients with AF compared with healthy subjects . Digoxin (2.4 ng/mL) induced calcium mobilization, PAC -1 (procaspase-activating compound 1) and platelet aggregation in AF patients but not in healthy subjects . After pretreatment with a sub-threshold of collagen, digoxin dose-dependent induced calcium mobilization, arachidonic acid release, TxB biosynthesis, PAC -1 and soluble platelet selectin expression, and platelet aggregation, which were inhibited by antibody against digoxin. Conclusions We found a significant in vivo correlation between SDC and platelet activation. Supratherapeutic SDC increased in vitro platelet aggregation via calcium-related phospholipase A phosphorylation. Our findings may have clinical implications for AF patients treated with digoxin.

Silvia Piconese

Department of Internal Medicine - DMISM

sapienza university

Inducing and Characterizing Vesicular Steatosis in Differentiated HepaRG Cells