BackgroundAngiogenesis and vascular remodelling are crucial events in tissue repair mechanisms promoted by cell transplantation. Current evidence underscores the importance of the soluble factors secreted by stem cells in tissue regeneration. In the present study we investigated the effects of paracrine factors derived from cultured endothelial progenitor cells (EPC) on rat brain endothelial cell properties and addressed the signaling pathways involved.MethodsEndothelial cells derived from rat brain (rBCEC4) were incubated with EPC-derived conditioned medium (EPC-CM). The angiogenic response of rBCEC4 to EPC-CM was assessed as effect on cell number, migration and tubular network formation. In addition, we have compared the outcome of the in vitro experiments with the effects on capillary sprouting from rat aortic rings. The specific PI3K/AKT inhibitor LY294002 and the MEK/ERK inhibitor PD98059 were used to study the involvement of these two signaling pathways in the transduction of the angiogenic effects of EPC-CM.ResultsViable cell number, migration and tubule network formation were significantly augmented upon incubation with EPC-CM. Similar findings were observed for aortic ring outgrowth with significantly longer sprouts. The EPC-CM-induced activities were significantly reduced by the blockage of the PI3K/AKT and MEK/ERK signaling pathways. Similarly to the outcome of the rBCEC4 experiments, inhibition of the PI3K/AKT and MEK/ERK pathways significantly interfered with capillary sprouting induced by EPC-CM.ConclusionThe present study demonstrates that EPC-derived paracrine factors substantially promote the angiogenic response of brain microvascular endothelial cells. In addition, our findings identified the PI3K/AKT and MEK/ERK pathways to play a central role in mediating these effects.

IntroductionThe unprecedented COVID-19 pandemic has exposed healthcare professionals (HCPs) to exceptional situations that can lead to increased anxiety (ie, infection anxiety and perceived vulnerability), traumatic stress and depression. We will investigate the development of these psychological disturbances in HCPs at the treatment front line and second line during the COVID-19 pandemic over a 12-month period in different countries. Additionally, we will explore whether personal resilience factors and a work-related sense of coherence influence the development of mental health problems in HCPs.Methods and analysisWe plan to carry out a sequential qualitative–quantitative mixed-methods design study. The quantitative phase consists of a longitudinal online survey based on six validated questionnaires, to be completed at three points in time. A qualitative analysis will follow at the end of the pandemic to comprise at least nine semistructured interviews. The a priori sample size for the survey will be a minimum of 160 participants, which we will extend to 400, to compensate for dropout. Recruitment into the study will be through personal invitations and the ‘snowballing’ sampling technique. Hierarchical linear regression combined with qualitative data analysis, will facilitate greater understanding of any associations between resilience and mental health issues in HCPs during pandemics.Ethics and disseminationThe study participants will provide electronic informed consent. All recorded data will be stored on a secured research server at the study site, which will only be accessible to the investigators. The Bern Cantonal Ethics Committee has waiv ed the need for ethical approval (Req-2020–00355, 1 April 2020). There are no ethical, legal or security issues regarding the data collection, processing, storage and dissemination in this project.Trial registration numberISRCTN13694948.

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