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A critical stage of T cell development is β-selection; at this stage, the T cell receptor β (TCRβ) chain is generated, and the developing T cell starts to acquire antigenic specificity. Progression through β-selection is assisted by low-affinity interactions between the nascent TCRβ chain and peptide presented on stromal major histocompatibility complex and cues provided by the niche. In this study, we identify a cue within the developing T cell niche that is critical for T cell development. E-cadherin mediates cell-cell interactions and influences cell fate in many developmental systems. In developing T cells, E-cadherin contributed to the formation of an immunological synapse and the alignment of the mitotic spindle with the polarity axis during division, which facilitated subsequent T cell development. Collectively, these data suggest that E-cadherin facilitates interactions with the thymic niche to coordinate the β-selection stage of T cell development.

Ultrashort self-assembling peptides of typically less than 5 amino acids in length can be modified with highly aromatic protecting groups such as Fluorenylmethyloxycarbonyl (Fmoc) resulting in the rapid formation of nanofibrillar hydrogels. These hydrogels show great promise as scaffolds for tissue engineering and 3D cell culture. If further modified with bioactive peptide sequences, the hydrogels can be used to promote and control cell adhesion, and even support the ability for cultured mesenchymal stem cells (MSCs) to differentiate into therapeutically useful lineages, such as chondrocytes. Whilst there have been numerous examples of how the addition of such sequences can promote the bioactivity of cultured cells, the effect adding these sequences has on the nanoarchitecture, mechanical properties and stability of the resultant hydrogels is less well explored. Here, we have performed a series of experiments investigating the effect incorporating stoichiometric amounts of Fmoc-Arg-Gly-Asp (Fmoc-RGD) into Fmoc-Phe-Phe (Fmoc-FF) hydrogels has on nanofibril morphology, and the rheological properties and stability of the formed gels. Furthermore, we correlate these variations in nano-architectural and mechanical properties with their ability to support the culture of clinically valuable bone marrow derived human mesenchymal stem cells (hMSCs). Our results show that at relatively low concentrations Fmoc-RGD is incorporated into the self-assembled Fmoc-FF nanofibrils creating biocompatible hydrogels capable of supporting hMSC growth for up to a week. At increased concentrations of Fmoc-RGD, incorporation into the nanofibrils is lost and the hydrogels that form are no longer stable enough to support the culture of hMSCs for multiple days. These findings shed light on the importance of balancing the positive effects of adding bioactive ligands to 3D scaffolds with the negative effects these ligands can have on the stability and mechanical properties of these scaffolds. Further, the findings will have implications for the choice of ultrashort peptide scaffolds for tissue engineering applications to support MSCs towards chondrogenic differentiation, and their application as gel-cell constructs in cartilage tissue engineering for osteoarthritis.

A critical stage of T cell development is β-selection; at this stage the TCRβ chain is generated and the developing T cell starts to acquire antigenic specificity. Progression through β-selection is assisted by a low affinity interaction between the nascent TCRβ chain and peptide presented on stromal MHC and external cues provided by the niche, including Notch and CXCR4. In this study, we reveal the importance of a new cue within the murine developing T cell niche which is critical for T cell development. E-cadherin mediates cell-cell interactions and influences cell fate in many developmental systems. In developing T cells E-cadherin contributed to the formation of an immunological synapse and the alignment of the mitotic spindle with the polarity axis during division, which facilitated subsequent T cell development. Collectively, these data highlight a new aspect of the developing T cell niche and provide insights into the role of E-cadherin in the β-selection stage of T cell development.

COVID-19 is primarily known as a respiratory disease caused by the virus SARS-CoV-2. However, neurological symptoms such as memory loss, sensory confusion, cognitive and psychiatric issues, severe headaches, and even stroke are reported in as many as 30% of cases and can persist even after the infection is over (so-called ‘long COVID’). These neurological symptoms are thought to be caused by brain inflammation, triggered by the virus infecting the central nervous system of COVID-19 patients, however we still don’t fully understand the mechanisms for these symptoms. The neurological effects of COVID-19 share many similarities to neurodegenerative diseases such as Alzheimer’s and Parkinson’s in which the presence of cytotoxic protein-based amyloid aggregates is a common etiological feature. Following the hypothesis that some neurological symptoms of COVID-19 may also follow an amyloid etiology we performed a bioinformatic scan of the SARS-CoV-2 proteome, detecting peptide fragments that were predicted to be highly amyloidogenic. We selected two of these peptides and discovered that they do rapidly self-assemble into amyloid. Furthermore, these amyloid assemblies were shown to be highly toxic to a neuronal cell line. We introduce and support the idea that cytotoxic amyloid aggregates of SARS-CoV-2 proteins are causing some of the neurological symptoms commonly found in COVID-19 and contributing to long COVID, especially those symptoms which are novel to long COVID in contrast to other post-viral syndromes.

During T cell development, the first step in creating a unique T Cell Receptor (TCR) is the genetic recombination of the TCRβ chain. The quality of the newly recombined TCRβ is assessed at the β-selection checkpoint. Most cells fail this checkpoint and die, but the coordination of the complex events that control fate at the β-selection checkpoint is not yet understood. We shed new light on fate determination during β-selection using a selective inhibitor of histone deacetylase 6, ACY1215. ACY1215 disrupted the β-selection checkpoint. Characterising the basis for this disruption revealed a new, pivotal stage in β-selection, bookended by upregulation of the TCR co-receptors, CD28 and CD2 respectively. Within this ‘DN3bPre’stage, CD5 and Lef1 are upregulated to reflect pre-TCR signalling and their expression correlates with proliferation. During this phase, ACY1215-mediated disruption of the organisation of the β-selection immunological synapse is associated with a breakdown in connectivity of expression of pre-TCR, CD5 and Lef1. Subsequent deregulation of pre-TCR-induced proliferation leads to bypass of the β-selection checkpoint and subsequent failure to progress. We propose that the progressive expression of CD28, CD5 and Lef1, then CD2 reports and modulates the pre-TCR signal to orchestrate passage through the β-selection checkpoint. These findings suggest a refined model of β-selection in which a coordinated increase in expression of pre-TCR, CD28, CD5 and Lef1 allows for modulating TCR signalling strength, and culminates in the expression of CD2 to enable exit from the β-selection checkpoint.

During T cell development, the first step in creating a unique T cell receptor (TCR) is genetic recombination of the TCRβ chain. The quality of the new TCRβ is assessed at the β-selection checkpoint. Most cells fail this checkpoint and die, but the coordination of fate at the β-selection checkpoint is not yet understood. We shed new light on fate determination during β-selection using a selective inhibitor of histone deacetylase 6, ACY1215. ACY1215 disrupted the β-selection checkpoint. Characterising the basis for this disruption revealed a new, pivotal stage in β-selection, bookended by up-regulation of TCR co-receptors, CD28 and CD2, respectively. Within this “DN3bPre” stage, CD5 and Lef1 are up-regulated to reflect pre-TCR signalling, and their expression correlates with proliferation. These findings suggest a refined model of β-selection in which a coordinated increase in expression of pre-TCR, CD28, CD5 and Lef1 allows for modulating TCR signalling strength and culminates in the expression of CD2 to enable exit from the β-selection checkpoint.