Parp1 hyperactivity couples DNA breaks to aberrant neuronal calcium signalling and lethal seizures.

Defects in DNA single-strand break repair (SSBR) are linked with neurological dysfunction but the underlying mechanisms remain poorly understood. Here, we show that hyperactivity of the DNA strand break sensor protein Parp1 in mice in which the central SSBR protein Xrcc1 is conditionally deleted (Xrcc1Nes-Cre ) results in lethal seizures and shortened lifespan. Using electrophysiological recording and synaptic imaging approaches, we demonstrate that aberrant Parp1 activation triggers seizure-like activity in Xrcc1-defective hippocampus ex vivo and deregulated presynaptic calcium signalling in isolated hippocampal neurons in vitro. Moreover, we show that these defects are prevented by Parp1 inhibition or deletion and, in the case of Parp1 deletion, that the lifespan of Xrcc1Nes-Cre mice is greatly extended. This is the first demonstration that lethal seizures can be triggered by aberrant Parp1 activity at unrepaired SSBs, highlighting PARP inhibition as a possible therapeutic approach in hereditary neurological disease.

The receptor-type protein tyrosine phosphatase CD45 promotes onset and severity of IL-1ß-mediated autoinflammatory osteomyelitis.

A number of human autoinflammatory diseases manifest with severe inflammatory bone destruction. Mouse models of these diseases represent valuable tools that help us to understand molecular mechanisms triggering this bone autoinflammation. The Pstpip2cmo mouse strain is among the best characterized of these; it harbors a mutation resulting in the loss of adaptor protein PSTPIP2 and development of autoinflammatory osteomyelitis. In Pstpip2cmo mice, overproduction of interleukin-1ß (IL-1ß) and reactive oxygen species by neutrophil granulocytes leads to spontaneous inflammation of the bones and surrounding soft tissues. However, the upstream signaling events leading to this overproduction are poorly characterized. Here, we show that Pstpip2cmo mice deficient in major regulator of Src-family kinases (SFKs) receptor-type protein tyrosine phosphatase CD45 display delayed onset and lower severity of the disease, while the development of autoinflammation is not affected by deficiencies in Toll-like receptor signaling. Our data also show deregulation of pro-IL-1ß production by Pstpip2cmo neutrophils that are attenuated by CD45 deficiency. These data suggest a role for SFKs in autoinflammation. Together with previously published work on the involvement of protein tyrosine kinase spleen tyrosine kinase, they point to the role of receptors containing immunoreceptor tyrosine-based activation motifs, which after phosphorylation by SFKs recruit spleen tyrosine kinase for further signal propagation. We propose that this class of receptors triggers the events resulting in increased pro-IL-1ß synthesis and disease initiation and/or progression.

Mechanisms determining a differential threshold for sensing Src family kinase activity by B and T cell antigen receptors.

Although signal transduction by immunoreceptors such as the T cell antigen receptor (TCR), B cell antigen receptor (BCR), and Fc receptors uses the same schematic and similar molecules, the threshold and the fine-tuning are set differently for each receptor. One manifestation of these differences is that inhibition of Src family kinases (SFK) blocks TCR but not BCR signaling. SFKs are key kinases phosphorylating immunoreceptor tyrosine-based activation motifs (ITAM) in both these receptors. However, it has been proposed that in B cells, downstream kinase SYK can phosphorylate ITAM sequences independently of SFK, allowing it to compensate for the loss of SFK activity, whereas its T cell paralog ZAP-70 is not capable of this compensation. To test this proposal, we examined signaling in SYK- and ZAP-70-deficient B and T cell lines expressing SYK or ZAP-70. We also analyzed signal transduction in T cells expressing BCR or B cells expressing part of the TCR complex. We show that when compared with ZAP-70, SYK lowered the threshold for SFK activity necessary to initiate antigen receptor signaling in both T and B cells. However, neither SYK nor ZAP-70 were able to initiate signaling independently of SFK. We further found that additional important factors are involved in setting this threshold. These include differences between the antigen receptor complexes themselves and the spatial separation of the key transmembrane adaptor protein LAT from the TCR. Thus, immunoreceptor sensing of SFK activity is a complex process regulated at multiple levels.