Biomedical subjects

Anselm A Zdebik

Publications and source records attributed to Anselm A Zdebik.

6 recordsLinked to original sources

PubMed2006

Lysosomal storage disease upon disruption of the neuronal chloride transport protein ClC-6.

Mammalian CLC proteins function as Cl(-) channels or as electrogenic Cl(-)/H(+) exchangers and are present in the plasma membrane and intracellular vesicles. We now show that the ClC-6 protein is almost exclusively expressed in neurons of the central and peripheral nervous systems, with a particularly high expression in dorsal root ganglia. ClC-6 colocalized with markers for late endosomes in neuronal cell bodies. The disruption of ClC-6 in mice reduced their pain sensitivity and caused moderate behavioral abnormalities. Neuronal tissues showed autofluorescence at initial axon segments. At these sites, electron microscopy revealed electron-dense storage material that caused a pathological enlargement of proximal axons. These deposits were positive for several lysosomal proteins and other marker proteins typical for neuronal ceroid lipofuscinosis (NCL), a lysosomal storage disease. However, the lysosomal pH of Clcn6(-/-) neurons appeared normal. CLCN6 is a candidate gene for mild forms of human NCL. Analysis of 75 NCL patients identified ClC-6 amino acid exchanges in two patients but failed to prove a causative role of CLCN6 in that disease.

Animals↗

PubMed2005

Voltage-dependent electrogenic chloride/proton exchange by endosomal CLC proteins.

Eukaryotic members of the CLC gene family function as plasma membrane chloride channels, or may provide neutralizing anion currents for V-type H(+)-ATPases that acidify compartments of the endosomal/lysosomal pathway. Loss-of-function mutations in the endosomal protein ClC-5 impair renal endocytosis and lead to kidney stones, whereas loss of function of the endosomal/lysosomal protein ClC-7 entails osteopetrosis and lysosomal storage disease. Vesicular CLCs have been thought to be Cl- channels, in particular because ClC-4 and ClC-5 mediate plasma membrane Cl- currents upon heterologous expression. Here we show that these two mainly endosomal CLC proteins instead function as electrogenic Cl-/H+ exchangers (also called antiporters), resembling the transport activity of the bacterial protein ClC-e1, the crystal structure of which has already been determined. Neutralization of a critical glutamate residue not only abolished the steep voltage-dependence of transport, but also eliminated the coupling of anion flux to proton counter-transport. ClC-4 and ClC-5 may still compensate the charge accumulation by endosomal proton pumps, but are expected to couple directly vesicular pH gradients to Cl- gradients.

Animals↗

PubMed2005

Physiological functions of CLC Cl- channels gleaned from human genetic disease and mouse models.

The CLC gene family encodes nine different Cl() channels in mammals. These channels perform their functions in the plasma membrane or in intracellular organelles such as vesicles of the endosomal/lysosomal pathway or in synaptic vesicles. The elucidation of their cellular roles and their importance for the organism were greatly facilitated by mouse models and by human diseases caused by mutations in their respective genes. Human mutations in CLC channels are known to cause diseases as diverse as myotonia (muscle stiffness), Bartter syndrome (renal salt loss) with or without deafness, Dent's disease (proteinuria and kidney stones), osteopetrosis and neurodegeneration, and possibly epilepsy. Mouse models revealed blindness and infertility as further consequences of CLC gene disruptions. These phenotypes firmly established the roles CLC channels play in stabilizing the plasma membrane voltage in muscle and possibly in neurons, in the transport of salt and fluid across epithelia, in the acidification of endosomes and synaptic vesicles, and in the degradation of bone by osteoclasts.

Animals↗

PubMed2005

Chloride channel diseases resulting from impaired transepithelial transport or vesicular function.

The transport of anions across cellular membranes is crucial for various functions, including the control of electrical excitability of muscle and nerve, transport of salt and water across epithelia, and the regulation of cell volume or the acidification and ionic homeostasis of intracellular organelles. Given this broad range of functions, it is perhaps not surprising that mutations in Cl- channels lead to a large spectrum of diseases. These diverse pathologies include the muscle disorder myotonia, cystic fibrosis, renal salt loss in Bartter syndrome, kidney stones, deafness, and the bone disease osteopetrosis. This review will focus on diseases related to transepithelial transport and on disorders involving vesicular Cl- channels.

Animals↗

PubMed2004

Additional disruption of the ClC-2 Cl(-) channel does not exacerbate the cystic fibrosis phenotype of cystic fibrosis transmembrane conductance regulator mouse models.

Cystic fibrosis is a fatal inherited disease that is caused by mutations in the gene encoding a cAMP-activated chloride channel, the cystic fibrosis transmembrane conductance regulator (CFTR). It has been suggested that the cystic fibrosis phenotype might be modulated by the presence of other Cl(-) channels that are coexpressed with CFTR in some epithelial cells. Because the broadly expressed plasma membrane Cl(-) channel, ClC-2, is present in the tissues whose function is compromised in cystic fibrosis, we generated mice with a disruption of both Cl(-) channel genes. No morphological changes in their intestine, lung, or pancreas, tissues affected by cystic fibrosis, were observed in these mice. The mortality was not increased over that observed with a complete lack of functional CFTR. Surprisingly, mice expressing mutant CFTR (deletion of phenylalanine 508), survived longer when ClC-2 was disrupted additionally. Currents across colonic epithelia were investigated in Ussing chamber experiments. The disruption of ClC-2, in addition to CFTR, did not decrease Cl(-) secretion. Colon expressing wild-type CFTR even secreted more Cl(-) when ClC-2 was disrupted, although CFTR transcript levels were unchanged. It is concluded that ClC-2 is unlikely to be a candidate rescue channel in cystic fibrosis. Our data are consistent with a model in which ClC-2 is located in the basolateral membrane.

Animals↗

PubMed2002

Molecular structure and physiological function of chloride channels.

Cl- channels reside both in the plasma membrane and in intracellular organelles. Their functions range from ion homeostasis to cell volume regulation, transepithelial transport, and regulation of electrical excitability. Their physiological roles are impressively illustrated by various inherited diseases and knock-out mouse models. Thus the loss of distinct Cl- channels leads to an impairment of transepithelial transport in cystic fibrosis and Bartter's syndrome, to increased muscle excitability in myotonia congenita, to reduced endosomal acidification and impaired endocytosis in Dent's disease, and to impaired extracellular acidification by osteoclasts and osteopetrosis. The disruption of several Cl- channels in mice results in blindness. Several classes of Cl- channels have not yet been identified at the molecular level. Three molecularly distinct Cl- channel families (CLC, CFTR, and ligand-gated GABA and glycine receptors) are well established. Mutagenesis and functional studies have yielded considerable insights into their structure and function. Recently, the detailed structure of bacterial CLC proteins was determined by X-ray analysis of three-dimensional crystals. Nonetheless, they are less well understood than cation channels and show remarkably different biophysical and structural properties. Other gene families (CLIC or CLCA) were also reported to encode Cl- channels but are less well characterized. This review focuses on molecularly identified Cl- channels and their physiological roles.

Animals↗