Functional role of connexins and gap junctional communication in endothelial repair

• Applicant: Professor Dr. Ulrich Pohl
• Subject Area: Anatomy and Physiology
• Term: from 2007 to 2012
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 46710789

• Final Report Year: 2013

Final Report Abstract

The aims of the funded project were to understand the influence of connexins and gap junctions on basal mechanisms of endothelial repair. We therefore studied the influence of connexins and gap junctions on cell migration, survival, calcium homeostasis and on the functional interaction between different types of vascular cells involved in key mechanisms of tissue repair. The experiments have yielded novel and unanticipated results. We have found for the first time that expression of histamine and purinergic receptors is inhomogeneously distributed in the endothelium both in culture and in intact vessels. Consequently, the calcium response of the endothelium to agonists of these receptors and the resulting NO production is highly dependent on the exchange of calcium and IP3 via endothelial gap junctions. Under conditions of reduced gap junctional communication (induced here by enhanced ROS production), the calcium-dependent vasomotor function of the endothelium is severely impaired. This is a new mechanism which may explain the contribution of endothelial impairment in a number of cardiovascular diseases known to be associated with altered connexin expression. We also discovered that the relative amount of cellular connexin expression and of the connexin type can decisively affect the rate of apoptosis elicited by the endogenous as well as the exogenous pathway, an important aspect to be considered in the future design of experiments involving endothelial repair. It also became evident that connexins regulate cellular functions beyond their role in gap junction channel formation. Using various model cell mutants and endothelial progenitor cells we could show that Cx43 enhanced cell migration in a completely gap junctionindependent manner. We found several proteins associated with Cx43, among them the actin capping protein Hsp27, which can potentially influence migration processes and cytoskeletal plasticity. Cx43 also enhanced p38 MAPK pathway signalling which resulted in enhanced filopodia formation. Currently we are investigating the functional role of connexins on cell migration of EPC in vivo using the dorsal skinfold chamber in mice allowing time series experiments over several days. Finally, following the hypothesis that pericytes may act as signal generators inducing endothelial hyperpolarisation and subsequent conduction of electric vasomotor signals along the endothelium of microvessels, we succeeded in isolation of pericytes from skeletal muscle and have identified all necessary mechanisms supporting the notion that gap junctional communication between pericytes and endothelial cells plays an integral role. Though unforeseen events required extension of the funding period and alteration of the original plans we have identified new roles of gap junctions with potential impact on vascular repair processes and laid the foundation for several ongoing follow-up studies in vitro and in vivo.

Publications

• Cells can exchange miRNA through Gap Junctions. Acta Physiologica 2009; Volume 195, Supplement 669, P271 (Abstract)
  Wallner S., Pogoda K., Pohl U
  
• Control of muscle blood flow during exercise: local factors and integrative mechanisms. Acta Physiol (Oxf)(2010) 199 (4):349-365
  Sarelius I, Pohl U
  
• The carboxyl tail of Cx43 augments p38 mediated cell migration in a gap junction-independent manner. Eur J Cell Biol.(2010) 89(11):828- 838
  Behrens J, Kameritsch P, Wallner S, Pohl U, Pogoda K
  
• A channel independent function of connexin 43 in cell migration
  Juliane Behrens
  
• Isolation and functional characterization of pericytes derived from hamster skeletal muscle. Acta Physiol (Oxf)(2011) 201(4):413-426
  Mogensen C, Bergner B, Wallner S, Ritter A, d'Avis S, Ninichuk V, Kameritsch P, Gloe T, Nagel W, Pohl U
  
• Channel-independent influence of connexin 43 on cell migration. Biochim Biophys Acta(2012) 1818(8):1993-2001
  Kameritsch P, Pogoda K, Pohl U
  
• Gap junctional communication controls the overall endothelial calcium response to vasoactive agonists. Cardiovasc Res (2012)93 (3):508- 515
  Kameritsch P, Pogoda K, Ritter A, Münzing S, Pohl U
  
• Skeletal muscles pericytes as signal mediators in the vessel wall – isolation and functional characterisation in hamster model
  Stefan Wallner
  
• Characterization of endothelial progenitor cell migration in vivo. J Physiol, 2013, 591: Suppl., 1070P (Abstract)
  Pircher J, Pogoda K, Pohl U
  
• Cx43 modulates cell migration and filopodia formation. International Gap Junction Conference 2013, Charleston, USA (Abstract)
  Pogoda K, Kameritsch P, Pohl, U
  
• Gap junctional communication promotes apoptosis in a connexin-type-dependent manner. Cell Death Dis(2013) 4:e584
  Kameritsch P, Khandoga N, Pohl U, Pogoda K
  
• NO selectively inhibits spreading of Ca2+ signals by targeting Cx37 enriched inmyoendothelial gap junctions. International Gap Junction Conference 2013, Charleston, USA (Abstract)
  Kameritsch P, Tanase L, Pogoda K, Pohl U