E2 pretreatment alleviates aggregation of intravenously injected mesenchymal stem cells in TBI by regulating BRG1 to affect adhesion

Abstract

Background Human umbilical cord mesenchymal stem cells (hUMSCs) are considered an effective prospect for treating TBI, but they tend to accumulate in the lungs after intravenous injection, hindering further clinical translation. Brahma-related gene 1(BRG1) can be influenced by estrogen to regulate adhesion, and ourprevious studies have found that the expression of BRG1 in lungs increases after TBI. However, the relationship between BRG1, estrogen, TBI, and stem cell lung aggregation is not clear. Methods By regulating the expression levels of BRG1 in vascular endothelial cells and hUMSCs, Western Blot and immunohistochemistry were used to explore its changes in adhesion and possible mechanisms; used in vivo bioluminescenece imaging analysis, real-time tracking the distribution of stem cells after transplantation; and therapeutic drug E2 is introduced to observe the effect of changes in BRG1 expression on the aggregation of hUMSCs in the lungs of model animals, as well as the therapeutic effect of E2-pretreated hUMSCs on inflammation after TBI. Results After TBI, the retention of hUMSCs in the lungs was higher in the TBI groups than in the Sham groups, and the level of BRG1 in lung was higher in the TBI groups than in the Sham groups; the expression of BRG1 in HUVECs, HPAECs, and hUMSCs treated with TNF-α and LPS were higher than those in the control groups, showing dose- and time-dependent effects. E2 can inhibit the expression of BRG1 and adhesion proteins; after intervention with estrogen receptor inhibitor (ICI 182780) and NF-κ B inhibitor SC75741, BRG1 expression increased and adhesion protein decreased; E2-pretreated MSCs can reduce pulmonary retention, and has no adverse effects on the inflammatory response for TBI.

1. Introduction

With the rapid development of modern transportation and construction, the incidence of traumatic brain injury (TBI) is increasing year by year, which is an important cause of functional disability [1, 2]. Historically conceptualized as an injury event with finite recovery, TBI is now recognized as a chronic condition that can affect multiple functional impairments, some of which might deteriorate over time [3]. How to reduce the mortality and sequelae of TBI has become a major problem in human society. Pathological changes after TBI mainly involve edema, inflammation, oxidative stress, apoptosis [4–6], thus the traditional methods for TBI treatment mainly include anti-infection, control of intracranial pressure, sedation and so on, but the effect is not ideal [2, 7]. In recent years, with the progress of biological science, many researchers found that mesenchymal stem cells (MSCs) can be used to treat TBI effectively [8, 9], which has attracted the attention of clinicians.

There are many methods for stem cell transplantation after TBI [9–12]. Intravenous injection is the most common, minimally invasive, and repeatable transplantation method, which has superior ethical and clinical practical application value [8, 11, 13]. However, after intravenous injection, stem cells tend to accumulate in the pulmonary capillary network to cause embolism [14–16], and our study also observed that TBI exacerbates this aggregation. The cause of MSCs pulmonary aggregation may relate to immune [17, 18], adhesion of transplanted microenvironment [19], status of transplanted cells [20], changes in blood composition [21, 22] or just the size of MSCs themselves [14]. But the exact mechanism is unclear, which hinders further clinical application.