Point mutations in connexin proteins can cause gain in hemichannel function (e.g., exacerbated hemichannel opening), which results in human pathologies, including deafness, skin disorders, cataract and Charcot-Marie-Tooth disease. Due to the large size and modest selectivity of the aqueous pore, exacerbated opening of connexin hemichannels at the plasma membrane leads to loss of electrochemical gradients and of small cytoplasmic metabolites, causing cell death. Control of hemichannel opening is indispensable, and is achieved by physiological extracellular Ca2+, which drastically reduces hemichannel activity. Aberrantly open hemichannels caused by connexin mutations are less sensitive to extracellular Ca2+. Some of these mutations are located at the intracellular site end of the pore, suggesting that they affect gating (opening and closing of the pore) rather than the Ca2+ binding site itself. To explain the relationship between these mutations and Ca2+ regulation in hemichannels, we hypothesize that Ca2+ binds to and stabilizes the closed hemichannel. Mutations that produce gain of function decrease occupancy of the closed state, rendering the channel less sensitive to Ca2+. The goal of this project is to identify the molecular basis of regulation of connexin hemichannels by external Ca2+ and the mechanistic basis of hemichannel gain of function induced by mutations in human connexin26 (hCx26) that cause disease. The crystal structure of the hCx26 channel was recently solved and will serve as a guide for structure-function studies. We hope that a better understanding of the mechanisms of gating and Ca2+ regulation of connexin channels will lead to development of drugs and other therapeutic approaches that can specifically correct or compensate for hemichannel gain of function, and hopefully serve, in the case of hCx26, to treat deafness and skin disorders caused by mutation of this connexin.

Public Health Relevance

Connexin channel mutations cause deafness, blindness, dermatological, neurological and developmental disorders. We seek to understand how the function of the connexin channels is changed by mutations so that therapeutic approaches to ameliorate the disorders can be designed.

Agency
National Institute of Health (NIH)
Institute
National Institute of General Medical Sciences (NIGMS)
Type
Research Project (R01)
Project #
5R01GM099490-02
Application #
8290512
Study Section
Neurotransporters, Receptors, and Calcium Signaling Study Section (NTRC)
Program Officer
Nie, Zhongzhen
Project Start
2011-07-01
Project End
2013-06-30
Budget Start
2012-07-01
Budget End
2013-06-30
Support Year
2
Fiscal Year
2012
Total Cost
$296,400
Indirect Cost
$106,400
Name
University of Medicine & Dentistry of NJ
Department
Pharmacology
Type
Schools of Medicine
DUNS #
623946217
City
Newark
State
NJ
Country
United States
Zip Code
07107
Lopez, William; Ramachandran, Jayalakshmi; Alsamarah, Abdelaziz et al. (2016) Mechanism of gating by calcium in connexin hemichannels. Proc Natl Acad Sci U S A 113:E7986-E7995
Gonzalez, J Patrick; Ramachandran, Jayalakshmi; Xie, Lai-Hua et al. (2015) Selective Connexin43 Inhibition Prevents Isoproterenol-Induced Arrhythmias and Lethality in Muscular Dystrophy Mice. Sci Rep 5:13490
Tong, Xuhui; Lopez, William; Ramachandran, Jayalakshmi et al. (2015) Glutathione release through connexin hemichannels: Implications for chemical modification of pores permeable to large molecules. J Gen Physiol 146:245-54
García, Isaac E; Maripillán, Jaime; Jara, Oscar et al. (2015) Keratitis-ichthyosis-deafness syndrome-associated Cx26 mutants produce nonfunctional gap junctions but hyperactive hemichannels when co-expressed with wild type Cx43. J Invest Dermatol 135:1338-47
Harris, Andrew L; Contreras, Jorge E (2014) Motifs in the permeation pathway of connexin channels mediate voltage and Ca (2+) sensing. Front Physiol 5:113
Lopez, William; Liu, Yu; Harris, Andrew L et al. (2014) Divalent regulation and intersubunit interactions of human connexin26 (Cx26) hemichannels. Channels (Austin) 8:1-4
Lopez, William; Gonzalez, Jorge; Liu, Yu et al. (2013) Insights on the mechanisms of Ca(2+) regulation of connexin26 hemichannels revealed by human pathogenic mutations (D50N/Y). J Gen Physiol 142:23-35