Cip1 .

Connexin 43 (Cx43) plays an important role in cardioprotective signalling by mechanisms at least in part independent of gap junctional communication. To investigate whether this role is related to specific properties of this connexin isoform, we used a knock-in mouse model in which the coding region of Cx43 is replaced by that of Cx32. Homozygous Cx43KI32 mice showed reduced cell-to-cell Lucifer Yellow transfer (P < 0.01), but QRS duration and left ventricular fractional shortening (echocardiography) were similar to those in wild-type animals. NMR spectroscopy detected reduced ATP and increased lactate content in myocardium from homozygous Cx43KI32 animals (P < 0.05). Despite this, isolated homozygous Cx43KI32 hearts showed smaller infarcts after ischaemia-reperfusion (40 min/60 min) as compared to hearts from heterozygous and wild-type animals (13 and 31% reduction, respectively, P < 0.05). Cardiac myocytes isolated from Cx43KI32 mouse hearts also showed a reduced rate of cell death after simulated ischaemia-reperfusion. In a separate series of experiments, both ischaemic (4 cycles of 3.5 min of ischaemia and 5 min of reperfusion) and pharmacological (50 μmol l −1 diazoxide, 10 min) preconditioning reduced infarct size in hearts from wild-type mice (by 24.84 and 26.63%, respectively, P < 0.05), but only ischaemic preconditioning was effective in hearts from heterozygous animals and both preconditioning strategies failed to protect Cx43KI32 homozygous hearts. These results demonstrate that Cx43 has an important and previously unknown modulatory effect in myocardial energy metabolism and tolerance to ischaemia, and plays a critical role in preconditioning protection, by mechanisms that are specific for this connexin isoform.

Polo-like kinase 1 (PLK1), an essential regulator of cell division, is currently undergoing clinical evaluation as a target for cancer therapy. We report an unexpected function of Plk1 in sustaining cardiovascular homeostasis. Plk1 haploinsufficiency in mice did not induce obvious cell proliferation defects but did result in arterial structural alterations, which frequently led to aortic rupture and death. Specific ablation of Plk1 in vascular smooth muscle cells (VSMCs) led to reduced arterial elasticity, hypotension, and an impaired arterial response to angiotensin II in vivo. Mechanistically, we found that Plk1 regulated angiotensin II-dependent activation of RhoA and actomyosin dynamics in VSMCs in a mitosis-independent manner. This regulation depended on Plk1 kinase activity, and the administration of small-molecule Plk1 inhibitors to angiotensin II-treated mice led to reduced arterial fitness and an elevated risk of aneurysm and aortic rupture. We thus conclude that a partial reduction of Plk1 activity that does not block cell division can nevertheless impair aortic homeostasis. Our findings have potentially important implications for current approaches aimed at PLK1 inhibition for cancer therapy.

The mechanisms maintaining adult lymphatic vascular specialization throughout life and their role in coordinating inter-organ communication to sustain homeostasis remain elusive. We report that inactivation of the mechanosensitive transcription factor Foxc2 in adult lymphatic endothelium leads to a stepwise intestine-to-lung systemic failure. Foxc2 loss compromised the gut epithelial barrier, promoted dysbiosis and bacterial translocation to peripheral lymph nodes, and increased circulating levels of purine metabolites and angiopoietin-2. Commensal microbiota depletion dampened systemic pro-inflammatory cytokine levels, corrected intestinal lymphatic dysfunction, and improved survival. Foxc2 loss skewed the specialization of lymphatic endothelial subsets, leading to populations with mixed, pro-fibrotic identities and to emergence of lymph node–like endothelial cells. Our study uncovers a cross-talk between lymphatic vascular function and commensal microbiota, provides single-cell atlas of lymphatic endothelial subtypes, and reveals organ-specific and systemic effects of dysfunctional lymphatics. These effects potentially contribute to the pathogenesis of diseases, such as inflammatory bowel disease, cancer, or lymphedema.

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BACKGROUND AND PURPOSEMitochondria are involved in the toxicity of several compounds, retro-control of gene expression and apoptosis activation. The effect of mitochondrial genome (mtDNA) depletion on changes in ABC transporter protein expression in response to bile acids and paracetamol was investigated. EXPERIMENTAL APPROACHHepa 1-6 mouse hepatoma cells with 70% decrease in 16S/18S rRNA ratio (Rho cells) were obtained by long-term treatment with ethidium bromide. KEY RESULTSSpontaneous apoptosis and reactive oxygen species (ROS) generation were decreased in Rho cells. Following glycochenodeoxycholic acid (GCDCA) or paracetamol, Rho cells generated less ROS and were more resistant to cell death. Apoptosis induced by GCDCA and Fas was also reduced. The basal expression of Mdr1 was significantly enhanced, but this was not further stimulated by GCDCA or paracetamol, as observed in wild-type (WT) cells. Basal expression of Mrp1 and Mrp4 was similar in WT and Rho cells, whereas they were up-regulated only in WT cells after GCDCA or paracetamol, along with the transcription factors Shp and Nrf2, but not Fxr or Pxr. Increased expression of Nrf2 was accompanied by its enhanced nuclear translocation. Glycoursodeoxycholic acid failed to cause any of the effects observed for GCDCA or paracetamol. CONCLUSIONS AND IMPLICATIONSThe Nrf2-mediated pathway is partly independent of ROS production. Nuclear translocation of Nrf2 is insufficient to up-regulate Mdr1, Mrp1 and Mrp4, which requires the participation of other regulatory element(s) whose activation in response to GCDCA and paracetamol is impaired in Rho cells and hence probably sensitive to ROS. AbbreviationsABC, ATP-binding cassette; CAR, constitutive androstane receptor; DCFH-DA, 2′,7′-dichlorofluorescein diacetate; FXR, farnesoid X receptor; GCDCA, glycochenodeoxycholic acid; GUDCA, glycoursodeoxycholic acid; MDR, multidrug resistance protein; MRP, multidrug resistance associated protein; NRF2, nuclear factor E2-related factor 2; PXR, pregnane X receptor; Rh123, rhodamine 123; SHP, small heterodimer partner; tBOOH, tert-butyl hydroperoxide

Small intestinal villi are structural and functional units present in higher vertebrates and uniquely adapted to nutrient absorption. Villus enterocytes are organized in transcriptional “zones” dedicated to specialized tasks such as absorption of specific nutrients. We report that the transcription factor c-MAF is expressed in differentiated lower and mid-villus enterocytes and is a target of BMP signaling. Maf inactivation perturbed the villus zonation program by increasing carbohydrate-related transcripts while suppressing transcripts linked to amino-acid and lipid absorption. The formation of cytoplasmic lipid droplets, shuttling dietary fat to chylomicrons, was impaired upon Maf loss indicating its role in dietary lipid handling. Maf inactivation under homeostatic conditions expanded tuft cells and led to compensatory gut lengthening, preventing weight loss. However, delayed Maf−/− enterocyte maturation impaired weight recovery after acute intestinal injury, resulting in reduced survival. Our results identify c-MAF as a regulator of the intestinal villus zonation program, while highlighting the importance of coordination between stem/progenitor and differentiation programs for intestinal regeneration.