Drosophila Mpv17 forms an ion channel and regulates energy metabolism

Mutations in MPV17 are a major contributor to mitochondrial DNA (mtDNA) depletion syndromes, a group of inherited genetic conditions due to mtDNA instability. To investigate the role of MPV17 in mtDNA maintenance, we generated and characterized a Drosophila melanogaster Mpv17 (dMpv17) KO model showing that the absence of dMpv17 caused profound mtDNA depletion in the fat body but not in other tissues, increased glycolytic flux and reduced lifespan in starvation. Accordingly, the expression of key genes of glycogenolysis and glycolysis was upregulated in dMpv17 KO flies. In addition, we demonstrated that dMpv17 formed a channel in planar lipid bilayers at physiological ionic conditions, and its electrophysiological hallmarks were affected by pathological mutations. Importantly, the reconstituted channel translocated uridine but not orotate across the membrane. Our results indicate that dMpv17 forms a channel involved in translocation of key metabolites and highlight the importance of dMpv17 in energy homeostasis and mitochondrial function.

Extracellular MicroRNA Signature of Human Helper T Cell Subsets in Health and Autoimmunity

Upon T cell receptor stimulation, CD4⁺ T helper (Th) lymphocytes release extracellular vesicles (EVs) containing microRNAs. However, no data are available on whether human CD4⁺ T cell subsets release EVs containing different pattern of microRNAs. The present work aimed at filling this gap by assessing the microRNA content in EVs released upon in vitro T cell receptor stimulation of Th1, Th17, and T regulatory (Treg) cells. Our results indicate that EVs released by Treg cells are significantly different compared with those released by the other subsets. In particular, miR-146a-5p, miR-150-5p, and miR-21-5p are enriched, whereas miR-106a-5p, miR-155-5p, and miR-19a-3p are depleted in Treg-derived EVs. The in vitro identified EV-associated microRNA signature was increased in serum of autoimmune patients with psoriasis and returned to healthy levels upon effective treatment with etanercept, a biological drug targeting the TNF pathway and suppressing inflammation. Moreover, Gene Set Enrichment Analysis showed an over-representation of genes relevant for T cell activation, such as CD40L, IRAK1, IRAK2, STAT1, and c-Myb in the list of validated targets of Treg-derived EV miRNAs. At functional level, Treg-derived (but not Th1/Th17-derived) EVs inhibited CD4⁺ T cell proliferation and suppressed two relevant targets of miR-146a-5p: STAT1 and IRAK2. In conclusion, our work identified the miRNAs specifically released by different human CD4⁺ T cell subsets and started to unveil the potential use of their quantity in human serum to mark the pathological elicitation of these cells in vivo and their biological effect in cell to cell communication during the adaptive immune response.

Abstract 1778: Characterization and anti-tumor functionality of a neuroblastoma-specific peptide, either free or conjugated to nanocarriers

Introduction. The identification of peptide ligands specific for solid tumors is expected to provide targeting moieties to improve delivery and to decrease toxicity of chemotherapy. We have recently identified the peptide HSYWLRS as a specific ligand for neuroblastoma (NB), a childhood tumor mostly refractory to current therapies.

Experimental procedures. The capability of peptide HSYWLRS to recognize NB cells was evaluated by coupling Qdot fluorescent nanoparticles with HSYWLRS or its scrambled version (SCR). NB cell association and internalization of HSYWLRS-targeted liposomes were tested by FACS and confocal microscopy studies. We further evaluated a potential role of this peptide in perturbing tumor-stroma interactions and tumor growth. NB cell lines stably transfected with eGFP were mixed with endothelial cells in the presence of either SCR or HSYWLRS peptides. Cell morphology and reciprocal cellular interactions were evaluated by optical and fluorescence microscopy. We finally performed therapeutic experiments with mice orthotopically injected with luc-trasfected NB cells and treated with HSYWLRS-targeted, doxorubicin-loaded liposomes (HSYWLRS-SL[DXR]). Anti-tumor efficacy was evaluated by BLI imaging. In vivo imaging was also performed by injecting mice with a bolus of fluorodeoxyglucose during a list mode acquisition lasting one hour using a dedicated micro-PET system. After framing rate optimization, tumor glucose consumption was measured using Patlak graphical approach and normalizing the slope of regression line for serum glucose level.

Results. FACS analysis showed that HSYWLRS-Qdot and SCR-Qdot bound NB cells in a dose-dependent manner, however with different intensity, being HSYWLRS-Qdot the more potent. The binding of HSYWLRS-Qdot was efficiently inhibited by an excess of HSYWLRS, but not by control SCR peptide. In contrast, the binding of SCR-Qdot was not inhibited neither by an excess of SCR nor by HSYWLRS peptide, suggesting that the binding of SCR-Qdot is not specific. Again, the specific peptide-driven binding of HSYWLRS-SL to NB cells was inhibited by an excess of HSYWLRS peptide. In all cases, HSYWLRS specifically altered in vitro the interactions of NB cells with endothelium. Similarly, this peptide statistically decreased tumor take and growth when co-injected with tumor cells in the adrenal gland of nude mice.

Preliminary in vivo results obtained by BLI and micro-PET devises indicated that HSYWLRS-SL[DXR] decrease tumor growth through a reduction of tumor glucose consumption, leading to an enhanced life span in treated mice.

Conclusion. Our findings demonstrate that HSYWLRS peptide recognizes NB cells and is functional in the design of nanocarriers with therapeutic efficacy paving the way to its clinical development.

Citation Format: Alice Bartolini, Monica Loi, Daniela Di Paolo, Laura Emionite, Angelina Sacchi, Flavio Curnis, Gianluca Bottoni, Michela Massollo, Cristina Gagliani, Silvia Bruno, Alessandro Gori, Renato Longhi, Michele Cilli, Carlo Tacchetti, Angelo Corti, Gianmario Sambuceti, Mirco Ponzoni, Serena Marchiò, Fabio Pastorino. Characterization and anti-tumor functionality of a neuroblastoma-specific peptide, either free or conjugated to nanocarriers. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 1778. doi:10.1158/1538-7445.AM2014-1778

Proteome profiling of neuroblastoma-derived exosomes reveal the expression of proteins potentially involved in tumor progression

Neuroblastoma (NB) is the most common extracranial solid tumor in childhood, with grim prognosis in a half of patients. Exosomes are nanometer-sized membrane vesicles derived from the multivesicular bodies (MVBs) of the endocytic pathway and released by normal and neoplastic cells. Tumor-derived exosomes have been shown in different model systems to carry molecules that promote cancer growth and dissemination. In this respect, we have here performed the first characterization and proteomic analysis of exosomes isolated from human NB cell lines by filtration and ultracentrifugation. Electron microscopy demonstrated that NB-derived exosomes exhibited the characteristic cup-shaped morphology. Dynamic light scattering studies showed a bell-shaped curve and a polydispersity factor consistent with those of exosomes. Zeta potential values suggested a good nanoparticle stability. We performed proteomic analysis of NB-derived exosomes by two dimension liquid chromatography separation and mass spectrometry analyses using the multidimensional protein identification technology strategy. We found that the large majority of the proteins identified in NB derived exosomes are present in Exocarta database including tetraspanins, fibronectin, heat shock proteins, MVB proteins, cytoskeleton-related proteins, prominin-1 (CD133), basigin (CD147) and B7-H3 (CD276). Expression of the CD9, CD63 and CD81 tetraspanins, fibronectin, CD133, CD147 and CD276 was validated by flow cytometry. Noteworthy, flow cytometric analysis showed that NB-derived exosomes expressed the GD2 disialoganglioside, the most specific marker of NB. In conclusion, this study shows that NB-derived exosomes express a discrete set of molecules involved in defense response, cell differentiation, cell proliferation and regulation of other important biological process. Thus, NB-derived exosomes may play an important role in the modulation of tumor microenvironment and represent potential tumor biomarkers.