Regulation of endothelial-specific transgene expression by the LacI repressor protein in vivo

Controlling CRISPR with small molecule regulation for somatic cell genome editing

Biomedical research has been revolutionized by the introduction of many CRISPR-Cas systems that induce programmable edits to nearly any gene in the human genome. Nuclease-based CRISPR-Cas editors can produce on-target genomic changes but can also generate unwanted genotoxicity and adverse events, in part by cleaving non-targeted sites in the genome. Additional translational challenges for in vivo somatic cell editing include limited packaging capacity of viral vectors and host immune responses. Altogether, these challenges motivate recent efforts to control the expression and activity of different Cas systems in vivo. Current strategies utilize small molecules, light, magnetism, and temperature to conditionally control Cas systems through various activation, inhibition, or degradation mechanisms. This review focuses on small molecules that can be incorporated as regulatory switches to control Cas genome editors. Additional development of CRISPR-Cas-based therapeutic approaches with small molecule regulation have high potential to increase editing efficiency with less adverse effects for somatic cell genome editing strategies in vivo.

Inducible and reversible silencing of the Pvalb gene in mice: An in vitro and in vivo study

Inducible and reversible regulation of gene expression is a powerful approach for unraveling gene functions. Here, we describe the generation of a system to efficiently downregulate in a reversible and inducible manner the Pvalb gene coding for the calcium-binding protein parvalbumin (PV) in mice. We made use of an IPTG-inducible short hairpin RNA to activate Pvalb transcript knockdown and subsequently downregulate PV. The downregulation was rapidly reversed after withdrawal of IPTG. In vitro and in vivo experiments revealed a decrease in PV expression of ≥50% in the presence of IPTG and full reversibility after IPTG removal. We foresee that the tightly regulated and reversible PV downregulation in mice in vivo will provide a new tool for the control of Pvalb transcript expression in a temporal manner. Because PV protein and PVALB transcript levels were found to be lower in the brain of patients with autism spectrum disorder and schizophrenia, the novel transgenic mouse line might serve as a model to investigate the putative role of PV in these neurodevelopmental disorders.

Generation of reporter hESCs by targeting EGFP at the CD144 locus to facilitate the endothelial differentiation

Reporter embryonic stem cell (ESC) lines with tissue-specific reporter genes may contribute to optimizing the differentiation conditions in vitro as well as trafficking transplanted cells in vivo. To optimize and monitor endothelial cell (EC) differentiation specifically, here we targeted the enhanced green fluorescent protein (EGFP) reporter gene at the junction of 5'UTR and exon2 of the endothelial specific marker gene CD144 using TALENs in human ESCs (H9) to generate a EGFP-CD144-reporter ESC line. The reporter cells expressed EGFP and CD144 increasingly and specifically without unexpected effects during the EC differentiation. The EC differentiation protocol was optimized and applied to EC differentiation from hiPSCs, resulting in an efficient and simplified endothelial differentiation approach. Here we created our own optimized and robust protocol for EC differentiation of hESCs and hiPSCs by generating the lineage-specific site-specific integration reporter cell lines, showing great potential to be applied in the fields such as trafficking gene and cell fate in vivo in preclinical animal models.

Peptide Uptake Is Essential for Borrelia burgdorferi Viability and Involves Structural and Regulatory Complexity of its Oligopeptide Transporter

Borrelia burgdorferi is an extreme amino acid (AA) auxotroph whose genome encodes few free AA transporters and an elaborate oligopeptide transport system (B. burgdorferi Opp [BbOpp]). BbOpp consists of five oligopeptide-binding proteins (OBPs), two heterodimeric permeases, and a heterodimeric nucleotide-binding domain (NBD). Homology modeling based on the crystal structure of liganded BbOppA4 revealed that each OBP likely binds a distinct range of peptides. Transcriptional analyses demonstrated that the OBPs are differentially and independently regulated whereas the permeases and NBDs are constitutively expressed. A conditional NBD mutant failed to divide in the absence of inducer and replicated in an IPTG (isopropyl-β-d-thiogalactopyranoside) concentration-dependent manner. NBD mutants grown without IPTG exhibited an elongated morphotype lacking division septa, often with flattening at the cell center due to the absence of flagellar filaments. Following cultivation in dialysis membrane chambers, NBD mutants recovered from rats not receiving IPTG also displayed an elongated morphotype. The NBD mutant was avirulent by needle inoculation, but infectivity was partially restored by oral administration of IPTG to infected mice. We conclude that peptides are a major source of AAs for B. burgdorferi both in vitro and in vivo and that peptide uptake is essential for regulation of morphogenesis, cell division, and virulence.

Borrelia burgdorferi, the causative agent of Lyme disease, is an extreme amino acid (AA) auxotroph with a limited repertoire of annotated single-AA transporters. A major issue is how the spirochete meets its AA requirements as it transits between its arthropod vector and mammalian reservoir. While previous studies have confirmed that the B. burgdorferi oligopeptide transport (opp) system is capable of importing peptides, the importance of the system for viability and pathogenesis has not been established. Here, we evaluated the opp system structurally and transcriptionally to elucidate its ability to import a wide range of peptides during the spirochete’s enzootic cycle. Additionally, using a novel mutagenesis strategy to abrogate opp transporter function, we demonstrated that peptide uptake is essential for bacterial viability, morphogenesis, and infectivity. Our studies revealed a novel link between borrelial physiology and virulence and suggest that peptide uptake serves an intracellular signaling function regulating morphogenesis and division.

Perturbation of chemical coupling by an endothelial Cx40 mutant attenuates endothelium-dependent vasodilation by KCa channels and elevates blood pressure in mice

Mutant forms of connexin40 (Cx40) exist in the human population and predispose carriers to atrial fibrillation. Since endothelial expression of Cx40 is important for electrical and chemical communication within the arterial wall, carriers of mutant Cx40 proteins may be predisposed to peripheral arterial dysfunction and dysregulation of blood pressure. We have therefore studied mice expressing either a chemically dysfunctional mutant, Cx40T202S, or wild-type Cx40, with native Cx40, specifically in the endothelium. Blood pressure was measured by telemetry under normal conditions and during cardiovascular stress induced by locomotor activity, phenylephrine or nitric oxide blockade (N(ɷ)-nitro-L-arginine methyl ester hydroxide, L-NAME). Blood pressure of Cx40T202STg mice was significantly elevated at night when compared with wild-type or Cx40Tg mice, without change in mean heart rate, pulse pressure or locomotor activity. Analysis over 24 h showed that blood pressure of Cx40T202STg mice was significantly elevated at rest and additionally during locomotor activity. In contrast, neither plasma renin concentration nor pressor responses to phenylephrine or L-NAME were altered, the latter indicating that nitric oxide bioavailability was normal. In isolated, pressurised mesenteric arteries, hyperpolarisation and vasodilation evoked by SKA-31, the selective modulator of SKCa and IKCa channels, was significantly reduced in Cx40T202STg mice, due to attenuation of the SKCa component. Acetylcholine-induced ascending vasodilation in vivo was also significantly attenuated in cremaster muscle arterioles of Cx40T202STg mice, compared to wild-type and Cx40Tg mice. We conclude that endothelial expression of the chemically dysfunctional Cx40T202S reduces peripheral vasodilator capacity mediated by SKCa-dependent hyperpolarisation and also increases blood pressure.

Loss of functional endothelial connexin40 results in exercise-induced hypertension in mice

During activity, coordinated vasodilation of microcirculatory networks with upstream supply vessels increases blood flow to skeletal and cardiac muscles and reduces peripheral resistance. Endothelial dysfunction in humans attenuates activity-dependent vasodilation, resulting in exercise-induced hypertension in otherwise normotensive individuals. Underpinning activity-dependent hyperemia is an ascending vasodilation in which the endothelial gap junction protein, connexin (Cx)40, plays an essential role. Because exercise-induced hypertension is proposed as a forerunner to clinical hypertension, we hypothesized that endothelial disruption of Cx40 function in mice may create an animal model of this condition. To this end, we created mice in which a mutant Cx40T152A was expressed alongside wildtype Cx40 selectively in the endothelium. Expression of the Cx40T152A transgene in Xenopus oocytes and mouse coronary endothelial cells in vitro impaired both electric and chemical conductance and acted as a dominant-negative against wildtype Cx40, Cx43, and Cx45, but not Cx37. Endothelial expression of Cx40T152A in Cx40T152ATg mice attenuated ascending vasodilation, without effect on radial coupling through myoendothelial gap junctions. Using radiotelemetry, Cx40T152ATg mice showed an activity-dependent increase in blood pressure, which was significantly greater than in wildtype mice, but significantly less than in chronically hypertensive, Cx40knockout mice. The increase in heart rate with activity was also greater than in wildtype or Cx40knockout mice. We conclude that the endothelial Cx40T152A mutation attenuates activity-dependent vasodilation, producing a model of exercise-induced hypertension. These data highlight the importance of endothelial coupling through Cx40 in regulating blood pressure during activity.