Deletion of the last five C-terminal amino acid residues of connexin43 leads to lethal ventricular arrhythmias in mice without affecting coupling via gap junction channels.

The cardiac intercalated disc harbors mechanical and electrical junctions as well as ion channel complexes mediating propagation of electrical impulses. Cardiac connexin43 (Cx43) co-localizes and interacts with several of the proteins located at intercalated discs in the ventricular myocardium. We have generated conditional Cx43D378stop mice lacking the last five C-terminal amino acid residues, representing a binding motif for zonula occludens protein-1 (ZO-1), and investigated the functional consequences of this mutation on cardiac physiology and morphology. Newborn and adult homozygous Cx43D378stop mice displayed markedly impaired and heterogeneous cardiac electrical activation properties and died from severe ventricular arrhythmias. Cx43 and ZO-1 were co-localized at intercalated discs in Cx43D378stop hearts, and the Cx43D378stop gap junction channels showed normal coupling properties. Patch clamp analyses of isolated adult Cx43D378stop cardiomyocytes revealed a significant decrease in sodium and potassium current densities. Furthermore, we also observed a significant loss of Nav1.5 protein from intercalated discs in Cx43D378stop hearts. The phenotypic lethality of the Cx43D378stop mutation was very similar to the one previously reported for adult Cx43 deficient (Cx43KO) mice. Yet, in contrast to Cx43KO mice, the Cx43 gap junction channel was still functional in the Cx43D378stop mutant. We conclude that the lethality of Cx43D378stop mice is independent of the loss of gap junctional intercellular communication, but most likely results from impaired cardiac sodium and potassium currents. The Cx43D378stop mice reveal for the first time that Cx43 dependent arrhythmias can develop by mechanisms other than impairment of gap junction channel function.

Quality control of astrocyte-directed Cre transgenic mice: the benefits of a direct link between loss of gene expression and reporter activation.

Cre recombinase activity for cell-type restricted deletion of floxed target genes (i.e., flanked by Cre recognition loxP-sites) is often measured by separate matings with recombination-activated reporter gene mice. Using a floxed Gja1 (Cx43) allele, we demonstrate the benefits of a direct link between reporter gene expression and target gene deletion to overcome critical limitations of the Cre/loxP system. The widely used human glial fibrillary acidic protein (hGFAP)-Cre transgene exhibits variable recombination activity and requires postexperimental validation. Such quality control is essential to correlate the extent of Cre-mediated Gja1 ablation with phenotypical alterations and to maintain the activity status of hGFAP-Cre in transgenic mouse colonies. We present several strategies to control for the fidelity of hGFAP-Cre mediated recombination. (c) 2008 Wiley-Liss, Inc.

Functional characterization of T-cells from palatine tonsils in patients with chronic tonsillitis.

The palatine tonsils, localized in the oropharynx, are easily accessible secondary lymphoid tissue in humans. Inflammation of the palatine tonsils, local and chronic in case of chronic tonsillitis (CT) or acute in the presence of a peritonsillar abscess (PTA), ranks among the most common diseases in otolaryngology. However, the functionality of tonsillar immune cells, notably T-cells, in the context of these immune pathologies is poorly understood. We have examined the functional status of human tonsillar T-cells in CT and compared it to the acute inflammatory setting of a PTA. Patients presenting with CT (n = 10) or unilateral PTA (n = 7) underwent bilateral tonsillectomy and a subgroup of 8 patients underwent additional blood sampling. T-cells were purified via automated magnetic selection and subjected to flow cytometry-based immunophenotyping. In addition, the response to T-cell receptor (TCR) stimulation was assessed at the level of proximal signaling, activation marker expression and proliferation. We observed no difference between the percentage of T helper (CD4(+)) cells from tonsil tissue in CT and PTA, but observed a trend towards a higher percentage of T helper cells in the blood of patients with PTA versus CT, probably reflecting an acute, systemic bacterial infection in the former cohort. Tonsils from CT harbored more PD-1(+) CD4(+) T-cells, pointing to T-cell exhaustion due to chronic infection. This notion was supported by functional studies that showed a tendency to weaker TCR responses of tonsillar T-cells from CT. Intriguingly, tonsillar T-cells recurrently featured a dampened response to T-cell receptor stimulation at the level of receptor proximal signaling steps compared to peripheral T-cells. In sum, our study documents distinct differences in tonsillar T-cell class distribution and function between the various pathological conditions. Our observations are consistent with the concept that tonsillar T-cells react to infections by eliciting specific immunological responses in chronic versus acute settings of inflammation.

Single cell analysis in native tissue: Quantification of the retinoid content of hepatic stellate cells.

Hepatic stellate cells (HSCs) are retinoid storing cells in the liver: The retinoid content of those cells changes depending on nutrition and stress level. There are also differences with regard to a HSC's anatomical position in the liver. Up to now, retinoid levels were only accessible from bulk measurements of tissue homogenates or cell extracts. Unfortunately, they do not account for the intercellular variability. Herein, Raman spectroscopy relying on excitation by the minimally destructive wavelength 785 nm is introduced for the assessment of the retinoid state of single HSCs in freshly isolated, unprocessed murine liver lobes. A quantitative estimation of the cellular retinoid content is derived. Implications of the retinoid content on hepatic health state are reported. The Raman-based results are integrated with histological assessments of the tissue samples. This spectroscopic approach enables single cell analysis regarding an important cellular feature in unharmed tissue.

Isolation of viable and functional T-cells from human palatine tonsils.

Increasing clinical evidence indicates that removal of the palatine tonsils enhances the risk for adults to suffer from severe illnesses. Together with recent experimental findings pointing to the presence of immunologically competent immune cells these findings illustrate that adult palatine tonsils likely play an appreciable role in the host immune response. T-cells are abundant in the palatine tonsil and are a pivotal entity of the adaptive immune response. However, investigation of T-cells from tonsils has been widely neglected and largely restricted to immune phenotyping. Accordingly, methodological literature describing the experimental preparation and isolation of T-cells from tonsils is scarce and has rarely been complemented with rigorous tests of T-cell functionality. We report here on a comparative investigation of three isolation protocols composed of permutations of different tissue grinding approaches, density gradient centrifugation and automated magnetic collection of CD4/CD8 T-cells. Importantly we put a strong emphasis on assessing the impact of the preparative procedures on the functionality of T-cells at the level of viability and functional response to T-cell receptor (TCR) ligation. The reported, optimized preparation protocols allow for the rapid isolation of highly viable, functional T-cells within 2.5h and represent a useful, affordable approach for the analysis of tonsillar T-cells.

Exploitation of the hepatic stellate cell Raman signature for their detection in native tissue samples.

Hepatic stellate cells (HSCs) surround liver sinusoids and store retinol while they are quiescent. During fibrotic liver diseases and acute-on-chronic liver failure they change to the activated state in which they proliferate, lose their retinol content and deposit extracellular matrix molecules. The process of HSC activation is of utmost interest, but so far only insufficiently understood, because there is a lack of techniques to address the function of single HSCs in the tissue context. In this contribution, the potential of Raman micro-spectroscopy for the label-free detection of HSCs in mouse liver samples is demonstrated. First, culture-induced activation of primary mouse HSCs is followed in vitro and characterized by means of Raman spectroscopy. The HSC activation state is confirmed by immunofluorescence labeling of glial fibrillary acidic protein (GFAP) and α-smooth muscle actin (ASMA). As expected, the unique Raman spectrum of retinol in quiescent HSCs is lost during activation. Nevertheless, successful discrimination of HSCs from primary hepatocytes is possible during all states of activation. A classification model based on principal component analysis followed by linear discriminant analysis (PCA-LDA) of the lipid droplet Raman data yields a prediction accuracy of 99%. The in vitro results are transferred to fresh liver slices and freshly sampled livers. Quiescent HSCs and a HSC transforming from quiescent to activated state are identified based on their Raman signature. This provides valuable information on HSC activation state in the liver.