The Role of KCNEs in mammalian physiology

The research in our laboratory is mainly focused on physiology and pathophysiology of KCNE genes with an emphasis on cardiovascular physiology. KCNEs are voltage-gated potassium (Kv) channel ancillary subunits that can form complexes with Kv channel a subunits (Figure 1) and modulate their functional properties such as gating, conductance, pharmacology and channel trafficking within the cell. KCNEs have recently gained a significant amount of attention from both scientists and clinicians because mutations in these genes have been identified and linked to serious human diseases such as the inherited and acquired long QT Syndrome (LQTS), but also neonatal epilepsy, schizophrenia, periodic paralysis, gastric adenocarcinoma and atrial fibrillation (Pongs et al., 2010). Apart from the association to human diseases relatively little is known about the molecular pathology that leads to KCNE associated diseases. Most of our knowledge about KCNE physiology stems from heterologous expression studies.



Figure 1. KCNE and α subunits of Kv-channels. (A) Transmembrane topology and (B) Proposed 4:2 stoichiometry (Chen et al., 2003) of α-KCNE Kv channel complexes. KCNE subunits are shown in red with N- and C-termini labeled, α subunits are in green.


In order to gain further insides on the precise molecular mechanisms underlying the above mentioned diseases and on how KCNEs modulate Kv channel α subunits in vivo we recently created kcne2 and kcne3 knockout mice (Roepke et al., 2006 and Roepke et al., 2011). In our lab we utilize a multidisciplinary approach to understand the molecular basis for KCNE function, how and why these ancillary potassium channels dysfunction, and how this leads to human disease.

 

Projects

KCNE subunits in gastro-intestinal epithelia

We were recently able to show that Kcne2 plays a pivotal in the production of gastric acid and that Kcne2 deletion in mice leads to a complete loss of gastric acid secretion (Roepke et al., 2006) which is due to a misstrafficking of  the KCNQ1 Kv channel a subunits (Figure 2) to the basolateral membrane of the gastric parietal cell – a compartment from which it cannot provide a sufficient K+ ion recycling current to support proper functioning of H+-K+-ATPase, the enzyme that is mainly responsible for gastric acidification (Roepke et al., 2011).


























Figure 2: Immunofluorescence showing basolateral distribution of Kv channel a subunit KCNQ1 in gastric parietal cells. A–C. Top: exemplar IF colabeling of Kcne2+/+ and Kcne2-/- gastric glands as indicated. “Merged” indicates merged view of the 2 panels above; bottom merged panel shows expanded view of the boxed region in the top merged panel. Yellow indicates colocalization. Blue arrowheads, PC basolateral side; white arrowheads, PC apical side. Representative of results from =2 mice, 3–5 sections/mouse/genotype. Bottom: cartoons summarizing IF data. A. Kcnq1 (red) and HKA ß subunit (green). B. Kcnq1 (red) and NKCC (green). C. HKA ß subunit (red) and NKCC (green).


Kcne2 deletion also leads to hypergastrinemia which in turn promotes gastric growth that leads to a preneoplastic phenotype named Gastritis Cystica Profunda (Figure 3).



















Figure 3: A. Photomicrograph of H&E-stained sections showing of gastric mucosa from Kcne2-/- mice demonstrating a preneoplastic phenotype named gastritis cystica profunda with three herniated glandular profiles in the submucosa. Arrows, vacuoles. *Cysts. Scale bar, 300 µm. B. Immunohistochemical staining for proliferation markers such as Ki67 indicates enhanced mucosal proliferation in Kcne2-/- gastric mucosa.



Current studies are focused on understanding the broad consequences of KCNE gene deletion on the different epithelial subcompartments along the GI tract.



KCNE subunits and cardiac arrhythmias

Mutations in KCNE subunits were also recently associated with cardiac arrhythmias such as the inherited and the acquired form of the long QT Syndrome (LQTS) and atrial fibrillation (AF). We were able to show that Kcne2 deletion leads to a prolonged action potential duration (Figure 4) resulting in a prolonged repolarization and lengthening of the QT interval on the body surface ECG (Roepke et al., 2008).

















Figure 4: Kcne2-/- mice exhibit prolonged ventricular action potential duration. A) Exemplar ventricular myocyte AP in Kcne2+/+ and Kcne2-/- mice recorded by optical mapping in isolated, perfused intact hearts.


We were also recently able to show that episodes of paroxysmal AF can be evoked by in vivo programmed electrical stimulation in Kcne2 and Kcne3 knockout mice. Ongoing studies are currently aimed to elucidate the molecular mechanisms that lead to this phenotype.




Techniques currently used in our laboratory


in vivo electrophysiology including Telemetry, ECG and Catheter-based EPU
cellular electrophysiology (Patch-Clamp)
Real-Time-quantitative PCR, Western Blot, Immunofluorescence, Histology  
Isolated perfused heart (Langendorff)
Calcium handling/Myocyte contraction studies (Ion-Optix)
Calcium Sparks - Confocal Microscopy


Funding

DFG
Fritz-Thyssen-Stiftung
Friede Springer Herz Stiftung
MDC/Charité