The bacterial TDP-43 IBs characterized here were found to be highly toxic to cultured neuronal cells, particularly following their internalization in the cytoplasm, where they are at least in part ubiquitinated and phosphorylated. A significant toxicity was found using intracellularly delivered IBs where TDP-43 was present at a concentration as low as 1.7 mg/mL before internalisation. It is debated whether aggregation of TDP-43 in the cytoplasm of ALS and FTLD-U patients causes neurodegeneration due to formation of toxic protein aggregates or to the translocation of TDP-43 from the nucleus, which represents its physiological location, to the cytoplasm, or both. Our results show that delivery of exogenous TDP-43 into the cytoplasm occurs in the absence of a significant loss of endogenous TDP-43 in the nucleus. Indeed, the images acquired after delivery show cytoplasmic TDP-43 in the absence of detectable clearance of nuclear TDP-43. Thus, the non-amyloid, amorphous aggregates formed from TDP-43 are inherently highly toxic to neuronal cells, indicating that a gain of function mechanism caused by TDP-43 deposits is effective in such pathology. The data do not exclude that a loss of function mechanism originating from the cellular mistrafficking of TDP-43 also contributes to pathology, but shows the Pimozide inherent toxicity of TDP-43 aggregates. In conclusion we have shown, using bacterial IBs containing aggregated TDP-43 as a model system, that both FL and Ct TDP43 aggregates consist of non-amyloid assemblies that have an intrinsically high ability to cause neuronal dysfunction when delivered into the cytoplasm, contributing to elucidate the pathogenesis of TDP-43 proteinopathies such as FTLD-U and ALS. Enhanced TCR-driven calcium mobilization was observed in human LYPW620 carriers and in T cells from a mouse carrying a Diperodon knock-in R619W mutation in mouse Pep that is homologous to the human LYP R620W variation. Chang et al. identified a new dominant-negative isoform of LYP and proposed a model that reconciles “gain-of-function” and “loss-of-function” observations. Dai et al. recently reported a phenotype of enhanced TCR signaling and spontaneous autoimmunity in R619W knock-in mice. Analysis of the spectrum of phosphorylated molecules in TCR-stimulated Pep-R619W T cells suggested altered enzymatic specificity. In line with this 
“altered function” model, a recent analysis of peripheral T cells from genotyped healthy subjects suggested that the LYP-R620W mutation can positively or negatively affect TCR signaling, depending on the biochemical readout assayed and on the stage of signaling. A prevailing model of thymocyte selection holds that TCR affinity for MHC/peptide ligand plays a central role in shaping the peripheral TCR repertoire. Deletion of autoreactive thymoyctes and agonist selection of regulatory T cells are two important mechanisms for establishing T cell tolerance that depend upon high-affinity interactions between TCR and ligand. Phenotyping of Ptpn22 knockout mice suggested that Pep might play a role in regulating thymic selection. Increased positive thymic selection has been reported in Ptpn22 KO mice and in two independently-generated Pep R619W knock-in mouse models, one of which developed spontaneous autoimmunity. Increased negative selection of H-Y transgenic male thymocytes mice was reported in one Pep R619W knock-in model, but thymic deletion was not altered in the other Pep R619W knock-in strain or in Ptpn22 KO mice. We reported increased TCR signaling in Ptpn22 KO thymocytes, correlating with increased thymic output of Treg in KO mice ; however, another group found no difference in thymic Treg percentages in an independently generated KO model.