Myeloid conditional deletion and transgenic models reveal a threshold for the neutrophil survival factor Serpinb1.

Serpinb1 is an inhibitor of neutrophil granule serine proteases cathepsin G, proteinase-3 and elastase. One of its core physiological functions is to protect neutrophils from granule protease-mediated cell death. Mice lacking Serpinb1a (Sb1a-/-), its mouse ortholog, have reduced bone marrow neutrophil numbers due to cell death mediated by cathepsin G and the mice show increased susceptibility to lung infections. Here, we show that conditional deletion of Serpinb1a using the Lyz2-cre and Cebpa-cre knock-in mice effectively leads to recombination-mediated deletion in neutrophils but protein-null neutrophils were only obtained using the latter recombinase-expressing strain. Absence of Serpinb1a protein in neutrophils caused neutropenia and increased granule permeabilization-induced cell death. We then generated transgenic mice expressing human Serpinb1 in neutrophils under the human MRP8 (S100A8) promoter. Serpinb1a expression levels in founder lines correlated positively with increased neutrophil survival when crossed with Sb1a-/- mice, which had their defective neutrophil phenotype rescued in the higher expressing transgenic line. Using new conditional and transgenic mouse models, our study demonstrates the presence of a relatively low Serpinb1a protein threshold in neutrophils that is required for sustained survival. These models will also be helpful in delineating recently described functions of Serpinb1 in metabolism and cancer.

SerpinB1 is critical for neutrophil survival through cell-autonomous inhibition of cathepsin G.

Bone marrow (BM) holds a large reserve of polymorphonuclear neutrophils (PMNs) that are rapidly mobilized to the circulation and tissues in response to danger signals. SerpinB1 is a potent inhibitor of neutrophil serine proteases neutrophil elastase (NE) and cathepsin G (CG). SerpinB1 deficiency (sB1(-/-)) results in a severe reduction of the BM PMN reserve and failure to clear bacterial infection. Using BM chimera, we found that serpinB1 deficiency in BM cells was necessary and sufficient to reproduce the BM neutropenia of sB1(-/-) mice. Moreover, we showed that genetic deletion of CG, but not NE, fully rescued the BM neutropenia in sB1(-/-) mice. In mixed BM chimera and in vitro survival studies, we showed that CG modulates sB1(-/-) PMN survival through a cell-intrinsic pathway. In addition, membrane permeabilization by lysosomotropic agent l-leucyl-l-leucine methyl ester that allows cytosolic release of granule contents was sufficient to induce rapid PMN death through a CG-dependent pathway. CG-mediated PMN cytotoxicity was only partly blocked by caspase inhibition, suggesting that CG cleaves a distinct set of targets during apoptosis. In conclusion, we have unveiled a new cytotoxic function for the serine protease CG and showed that serpinB1 is critical for maintaining PMN survival by antagonizing intracellular CG activity.

Cost-Utility of Internet-Based Cognitive Behavioral Therapy in Unipolar Depression: A Markov Model Simulation.

BACKGROUND AND OBJECTIVE: Unipolar depression is the most common form of depression and demand for treatment, such as psychotherapy, is high. However, waiting times for psychotherapy often considerably exceed their recommended maximum. As a potentially less costly alternative treatment, internet-based cognitive behavior therapy (ICBT) might help reduce waiting times. We therefore analyzed the cost-utility of ICBT compared to face-to-face CBT (FCBT) as an active control treatment, taking differences in waiting time into account. METHODS: We constructed a Markov model to simulate costs and health outcomes measured in quality-adjusted life years (QALYs) for ICBT and FCBT in Germany. We modeled a time horizon of 3 years using six states (remission, depressed, spontaneous remission, undergoing treatment, treatment finished, death). The societal perspective was adopted. We obtained parameters for transition probabilities, depression-specific QoL, and cost data from the literature. Deterministic and probabilistic sensitivity analyses were conducted. Within a scenario analysis, we simulated different time-to-treatment combinations. Half-cycle correction was applied. RESULTS: In our simulation, ICBT generated 0.260 QALYs and saved €2536 per patient compared to FCBT. Our deterministic sensitivity analysis suggests that the base-case results were largely unaffected by parameter uncertainty and are therefore robust. Our probabilistic sensitivity analysis suggests that ICBT is highly likely to be more effective (91.5%), less costly (76.0%), and the dominant strategy (69.7%) compared to FCBT. The scenario analysis revealed that the base-case results are robust to variations in time-to-treatment differences. CONCLUSION: ICBT has a strong potential to balance demand and supply of CBT in unipolar depression by reducing therapist time per patient. It is highly likely to generate more QALYs and reduce health care expenditure. In addition, ICBT may have further positive external effects, such as freeing up capacities for the most severely depressed patients.

SerpinB1 protects the mature neutrophil reserve in the bone marrow.

SerpinB1 is among the most efficient inhibitors of neutrophil serine proteases--NE, CG, and PR-3--and we investigated here its role in neutrophil development and homeostasis. We found that serpinB1 is expressed in all human bone marrow leukocytes, including stem and progenitor cells. Expression levels were highest in the neutrophil lineage and peaked at the promyelocyte stage, coincident with the production and packaging of the target proteases. Neutrophil numbers were decreased substantially in the bone marrow of serpinB1(-/-) mice. This cellular deficit was associated with an increase in serum G-CSF levels. On induction of acute pulmonary injury, neutrophils were recruited to the lungs, causing the bone marrow reserve pool to be completely exhausted in serpinB1(-/-) mice. Numbers of myeloid progenitors were normal in serpinB1(-/-) bone marrow, coincident with the absence of target protease expression at these developmental stages. Maturation arrest of serpinB1(-/-) neutrophils was excluded by the normal CFU-G growth in vitro and the normal expression in mature neutrophils of early and late differentiation markers. Normal absolute numbers of proliferating neutrophils and pulse-chase kinetic studies in vivo showed that the bone marrow deficit in serpinB1(-/-) mice was largely restricted to mature, postmitotic neutrophils. Finally, upon overnight culture, apoptosis and necrosis were greater in purified bone marrow neutrophils from serpinB1(-/-) compared with WT mice. Collectively, these findings demonstrate that serpinB1 sustains a healthy neutrophil reserve that is required in acute immune responses.