[show abstract][hide abstract] ABSTRACT: Calcium (Ca(2+)) is an universal second messenger that regulates the most important activities of all eukaryotic cells. It is of critical importance to neurons as it participates in the transmission of the depolarizing signal and contributes to synaptic activity. Neurons have thus developed extensive and intricate Ca(2+) signaling pathways to couple the Ca(2+) signal to their biochemical machinery. Ca(2+) influx into neurons occurs through plasma membrane receptors and voltage-dependent ion channels. The release of Ca(2+) from the intracellular stores, such as the endoplasmic reticulum, by intracellular channels also contributes to the elevation of cytosolic Ca(2+). Inside the cell, Ca(2+) is controlled by the buffering action of cytosolic Ca(2+)-binding proteins and by its uptake and release by mitochondria. The uptake of Ca(2+) in the mitochondrial matrix stimulates the citric acid cycle, thus enhancing ATP production and the removal of Ca(2+) from the cytosol by the ATP-driven pumps in the endoplasmic reticulum and the plasma membrane. A Na(+)/Ca(2+) exchanger in the plasma membrane also participates in the control of neuronal Ca(2+). The impaired ability of neurons to maintain an adequate energy level may impact Ca(2+) signaling: this occurs during aging and in neurodegenerative disease processes. The focus of this review is on neuronal Ca(2+) signaling and its involvement in synaptic signaling processes, neuronal energy metabolism, and neurotransmission. The contribution of altered Ca(2+) signaling in the most important neurological disorders will then be considered.
Cellular and Molecular Life Sciences CMLS 01/2014; · 5.62 Impact Factor
[show abstract][hide abstract] ABSTRACT: Mitochondria are key players of many physiological processes and deregulation of mitochondrial and/or mitochondria-related activity is unequivocally associated to numerous ageing-linked neurodegenerative disorders, including Parkinson's disease (PD), Alzheimer's disease (AD), and amyotrophic lateral sclerosis (ALS). Recently, the endoplasmic reticulum (ER) stress condition is emerging as a common feature relevant to the pathogenesis of this type of diseases. Mitochondria and ER are two compartments physically and functionally tightly interconnected and recent evidence revealed that the impairment in their communication might represent a common hit in different neurodegenerative diseases. ER-mitochondria contact sites are crucial for Ca2+ signaling since, upon the opening of ER Ca2+ release channels, microdomains of high [Ca2+] are generated in their proximity and Ca2+ can be taken up by the low-affinity mitochondrial uniporter. This transfer is essential in stimulated as well as in resting conditions to sustain cell metabolism and bioenergetics. Alterations in the ER-mitochondria juxtaposition are critical not only because they determine mitochondrial dysfunctions, but also because they compromise lipid metabolism, protein synthesis, and folding, thus demonstrating that the interaction between the two compartments is bi-functional. However, the functional consequences of these alterations on Ca2+ signaling and the possible involvement in the development of neurodegenerative conditions are currently largely unexplored. Here we will survey the recent literature in the field and discuss recent insights focusing on some cellular models expressing mutant proteins involved in the pathogenesis of familial forms of PD, AD, and ALS.
DNA and cell biology 03/2013; · 2.28 Impact Factor
[show abstract][hide abstract] ABSTRACT: DJ-1 was first identified as an oncogene. More recently, mutations in its gene have been found causative for autosomal recessive familial Parkinson disease. Numerous studies support the DJ-1 role in the protection against oxidative stress and maintenance of mitochondria structure; however, the mechanism of its protective function remains largely unknown. We investigated whether mitochondrial Ca2+ homeostasis, a key parameter in cell physiology, could be a target for DJ-1 action. Here, we show that DJ-1 modulates mitochondrial Ca2+ transients induced upon cell stimulation with an 1,4,5-inositol-tris-phosphate agonist by favouring the endoplasmic reticulum (ER)-mitochondria tethering. A reduction of DJ-1 levels results in mitochondria fragmentation and decreased mitochondrial Ca2+ uptake in stimulated cells. To functionally couple these effects with the well-recognized cytoprotective role of DJ-1, we investigated its action in respect to the tumour suppressor p53. p53 overexpression in HeLa cells impairs their ability to accumulate Ca2+ in the mitochondrial matrix, causes alteration of the mitochondrial morphology and reduces ER-mitochondria contact sites. Mitochondrial impairments are independent from Drp1 activation, since the co-expression of the dominant negative mutant of Drp1 failed to abolish them. DJ-1 overexpression prevents these alterations by re-establishing the ER-mitochondria tethering. Similarly, the co-expression of the pro-fusion protein Mitofusin 2 blocks the effects induced by p53 on mitochondria, confirming that the modulation of the ER-mitochondria contact sites is critical to mitochondria integrity. Thus, the impairment of ER-mitochondria communication, as a consequence of DJ-1 loss-of-function, may be detrimental for mitochondria-related processes and be at the basis of mitochondrial dysfunction observed in Parkinson disease.
Human Molecular Genetics 02/2013; · 7.69 Impact Factor
[show abstract][hide abstract] ABSTRACT: Loss-of-function mutations in PINK1 or parkin genes are associated with juvenile-onset autosomal recessive forms of Parkinson disease. Numerous studies have established that PINK1 and parkin participate in a common mitochondrial-quality control pathway, promoting the selective degradation of dysfunctional mitochondria by mitophagy. Upregulation of parkin mRNA and protein levels has been proposed as protective mechanism against mitochondrial and endoplasmic reticulum (ER) stress. To better understand how parkin could exert protective function we considered the possibility that it could modulate the ER-mitochondria inter-organelles cross talk. To verify this hypothesis we investigated the effects of parkin overexpression on ER-mitochondria crosstalk with respect to the regulation of two key cellular parameters: Ca(2+) homeostasis and ATP production. Our results indicate that parkin overexpression in model cells physically and functionally enhanced ER-mitochondria coupling, favoured Ca(2+) transfer from the ER to the mitochondria following cells stimulation with an 1,4,5 inositol trisphosphate (InsP(3)) generating agonist and increased the agonist-induced ATP production. The overexpression of a parkin mutant lacking the first 79 residues (ΔUbl) failed to enhance the mitochondrial Ca(2+) transients, thus highlighting the importance of the N-terminal ubiquitin like domain for the observed phenotype. siRNA-mediated parkin silencing caused mitochondrial fragmentation, impaired mitochondrial Ca(2+) handling and reduced the ER-mitochondria tethering. These data support a novel role for parkin in the regulation of mitochondrial homeostasis, Ca(2+) signaling and energy metabolism under physiological conditions.
Biochimica et Biophysica Acta 01/2013; · 4.66 Impact Factor
[show abstract][hide abstract] ABSTRACT: Ca(2+) is a universal carrier of biological information: it controls cell life from its origin at fertilization to its end in the process of programmed cell death. Ca(2+) is a conventional diffusible second messenger released inside cells by the interaction of first messengers with plasma membrane receptors. However, it can also penetrate directly into cells to deliver information without the intermediation of first or second messengers. Even more distinctively, Ca(2+) can act as a first messenger, by interacting with a plasma membrane receptor to set in motion intracellular signaling pathways that involve Ca(2+) itself. Perhaps the most distinctive property of the Ca(2+) signal is its ambivalence: while essential to the correct functioning of cells, Ca(2+) becomes an agent that mediates cell distress, or even (toxic) cell death, if its concentration and movements inside cells are not carefully tuned. Ca(2+) is controlled by reversible complexation to specific proteins, which could be pure Ca(2+) buffers, or which, in addition to buffering Ca(2+), also decode its signal to pass it on to targets. The most important actors in the buffering of cell Ca(2+) are proteins that transport it across the plasma membrane and the membrane of the organelles: some have high Ca(2+) affinity and low transport capacity (e.g., Ca(2+) pumps), others have opposite properties (e.g., the Ca(2+) uptake system of mitochondria). Between the initial event of fertilization, and the terminal event of programmed cell death, the Ca(2+) signal regulates the most important activities of the cell, from the expression of genes, to heart and muscle contraction and other motility processes, to diverse metabolic pathways involved in the generation of cell fuels.
[show abstract][hide abstract] ABSTRACT: Ca(2+) in neurons is vital to processes such as neurotransmission, neurotoxicity, synaptic development, and gene expression. Disruption of Ca(2+) homeostasis occurs in brain aging and in neurodegenerative disorders. Membrane transporters, among them the calmodulin (CaM)-activated plasma membrane Ca(2+) ATPases (PMCAs) that extrude Ca(2+) from the cell, play a key role in neuronal Ca(2+) homeostasis. Using X-exome sequencing we have identified a missense mutation (G1107D) in the CaM-binding domain of isoform 3 of the PMCAs in a family with X-linked congenital cerebellar ataxia. PMCA3 is highly expressed in the cerebellum, particularly in the presynaptic terminals of parallel fibers-Purkinje neurons. To study the effects of the mutation on Ca(2+) extrusion by the pump, model cells (HeLa) were cotransfected with expression plasmids encoding its mutant or wild-type (wt) variants and with the Ca(2+)-sensing probe aequorin. The mutation reduced the ability of the PMCA3 pump to control the cellular homeostasis of Ca(2+). It significantly slowed the return to baseline of the Ca(2+) transient induced by an inositol-trisphosphate (InsP(3))-linked plasma membrane agonist. It also compromised the ability of the pump to oppose the influx of Ca(2+) through the plasma membrane capacitative channels.
Proceedings of the National Academy of Sciences 08/2012; 109(36):14514-9. · 9.74 Impact Factor
[show abstract][hide abstract] ABSTRACT: Mitochondria are essential for ensuring numerous fundamental physiological processes such as cellular energy, redox balance, modulation of Ca(2+) signaling and important biosynthetic pathways. They also govern the cell fate by participating in the apoptosis pathway. The mitochondrial shape, volume, number and distribution within the cells are strictly controlled. The regulation of these parameters has an impact on mitochondrial function, especially in the central nervous system, where trafficking of mitochondria is critical to their strategic intracellular distribution, presumably according to local energy demands. Thus, the maintenance of a healthy mitochondrial population is essential to avoid the impairment of the processes they regulate: for this purpose, cells have developed mechanisms involving a complex system of quality control to remove damaged mitochondria, or to renew them. Defects of these processes impair mitochondrial function and lead to disordered cell function, i.e., to a disease condition. Given the standard role of mitochondria in all cells, it might be expected that their dysfunction would give rise to similar defects in all tissues. However, damaged mitochondrial function has pleiotropic effects in multicellular organisms, resulting in diverse pathological conditions, ranging from cardiac and brain ischemia, to skeletal muscle myopathies to neurodegenerative diseases. In this review, we will focus on the relationship between mitochondrial (and cellular) derangements and Ca(2+) dysregulation in neurodegenerative diseases, emphasizing the evidence obtained in genetic models. Common patterns, that recognize the derangement of Ca(2+) and energy control as a causative factor, have been identified: advances in the understanding of the molecular regulation of Ca(2+) homeostasis, and on the ways in which it could become perturbed in neurological disorders, may lead to the development of therapeutic strategies that modulate neuronal Ca(2+) signaling.
[show abstract][hide abstract] ABSTRACT: α-Synuclein has a central role in Parkinson disease, but its physiological function and the mechanism leading to neuronal degeneration remain unknown. Because recent studies have highlighted a role for α-synuclein in regulating mitochondrial morphology and autophagic clearance, we investigated the effect of α-synuclein in HeLa cells on mitochondrial signaling properties focusing on Ca(2+) homeostasis, which controls essential bioenergetic functions. By using organelle-targeted Ca(2+)-sensitive aequorin probes, we demonstrated that α-synuclein positively affects Ca(2+) transfer from the endoplasmic reticulum to the mitochondria, augmenting the mitochondrial Ca(2+) transients elicited by agonists that induce endoplasmic reticulum Ca(2+) release. This effect is not dependent on the intrinsic Ca(2+) uptake capacity of mitochondria, as measured in permeabilized cells, but correlates with an increase in the number of endoplasmic reticulum-mitochondria interactions. This action specifically requires the presence of the C-terminal α-synuclein domain. Conversely, α-synuclein siRNA silencing markedly reduces mitochondrial Ca(2+) uptake, causing profound alterations in organelle morphology. The enhanced accumulation of α-synuclein into the cells causes the redistribution of α-synuclein to localized foci and, similarly to the silencing of α-synuclein, reduces the ability of mitochondria to accumulate Ca(2+). The absence of efficient Ca(2+) transfer from endoplasmic reticulum to mitochondria results in augmented autophagy that, in the long range, could compromise cellular bioenergetics. Overall, these findings demonstrate a key role for α-synuclein in the regulation of mitochondrial homeostasis in physiological conditions. Elevated α-synuclein expression and/or eventually alteration of the aggregation properties cause the redistribution of the protein within the cell and the loss of modulation on mitochondrial function.
Journal of Biological Chemistry 03/2012; 287(22):17914-29. · 4.65 Impact Factor
[show abstract][hide abstract] ABSTRACT: DREAM is a Ca(2+)-dependent transcriptional repressor highly expressed in neuronal cells. A number of genes have already been identified as the target of its regulation. Targeted analysis performed on cerebella from transgenic mice expressing a dominant active DREAM mutant (daDREAM) showed a drastic reduction of the amount of transcript of Ca(2+)-activated nucleotidase 1 (CANT1), an endoplasmic reticulum (ER)-Golgi resident Ca(2+)-dependent nucleoside diphosphatase that has been suggested to have a role in glucosylation reactions related to the quality control of proteins in the ER and the Golgi apparatus. CANT1 down-regulation was also found in neuroblastoma SH-SY5Y cells stably overexpressing wild type (wt) DREAM or daDREAM, thus providing a simple cell model to investigate the protein maturation pathway. Pulse-chase experiments demonstrated that the down-regulation of CANT1 is associated with reduced protein secretion and increased degradation rates. Importantly, overexpression of wtDREAM or daDREAM augmented the expression of the EDEM1 gene, which encodes a key component of the ER-associated degradation pathway, suggesting an alternative pathway to enhanced protein degradation. Restoring CANT1 levels in neuroblastoma clones recovered the phenotype, thus confirming a key role of CANT1, and of the regulation of its gene by DREAM, in the control of protein synthesis and degradation.
Journal of Biological Chemistry 03/2012; 287(22):18478-91. · 4.65 Impact Factor
[show abstract][hide abstract] ABSTRACT: Hearing relies on the ability of the inner ear to convert sound waves into electrical signals. The main actors in this process are hair cells. Their stereocilia contain a number of specific proteins and a scaffold of actin molecules. They are organized in bundles by tip-link filaments composed of cadherin 23 and protocadherin 15. The bundle is deflected by sound waves leading to the opening of mechano-transduction channels and to the influx of K(+) and Ca(2+) into the stereocilia. Cadherin 23 and the plasma membrane calcium ATPase isoform 2 (PMCA2) are defective in human and murine cases of deafness. While the involvement of cadherin 23 in deafness/hearing could be expected due to its structural role in the tip-links, that of PMCA2 has been discovered only recently. This review will summarize the structural and functional characteristics of hair cells, focusing on the proteins whose mutations may lead to a deafness phenotype.
The international journal of biochemistry & cell biology 02/2012; 44(5):679-83. · 4.89 Impact Factor
[show abstract][hide abstract] ABSTRACT: Downstream regulatory element antagonist modulator (DREAM) is a Ca(2+)-binding protein that binds DNA and represses transcription in a Ca(2+)-dependent manner. Previous work has shown a role for DREAM in cerebellar function regulating the expression of the sodium/calcium exchanger 3 (NCX3) in cerebellar granular neurons to control Ca(2+) homeostasis and survival of these neurons. To achieve a global view of the genes regulated by DREAM in the cerebellum, we performed a genome-wide analysis in transgenic cerebellum expressing a Ca(2+)-insensitive/CREB-independent dominant active mutant DREAM (daDREAM). Here we show that DREAM regulates the expression of the midline 1 (Mid1) gene early after birth. As a consequence, daDREAM mice exhibit a significant shortening of the rostro-caudal axis of the cerebellum and a delay in neuromotor development early after birth. Our results indicate a role for DREAM in cerebellar function.
Frontiers in Molecular Neuroscience 01/2012; 5:58.
[show abstract][hide abstract] ABSTRACT: Mitochondria play a central role in cell biology, not only as producers of ATP but also as regulators of the Ca(2+) signal. The translocation by respiratory chain protein complexes of H(+) across the ion-impermeable inner membrane generates a very large H(+) electrochemical gradient that can be employed not only by the H(+) ATPase to run the endoergonic reaction of ADP phosphorylation, but also to accumulate cations into the matrix. Mitochondria can rapidly take up Ca(2+) through an electrogenic pathway, the uniporter, that acts to equilibrate Ca(2+) with its electrochemical gradient, and thus accumulates the cation into the matrix, and they can release it through two exchangers (with H(+) and Na(+), mostly expressed in non-excitable and excitable cells, respectively), that utilize the electrochemical gradient of the monovalent cations to prevent the attainment of electrical equilibrium.The uniporter, due to its low Ca(2+) affinity, demands high local Ca(2+) concentrations to work. In different cell systems these high Ca(2+) concentration microdomains are generated, upon cell stimulation, in proximity of the plasma membrane and the sarco/endoplasmic reticulum Ca(2+) channels.Recent work has revealed the central role of mitochondria in signal transduction pathways: evidence is accumulating that, by taking up Ca(2+), they not only modulate mitochondrial activities but also tune the cytosolic Ca(2+) signals and their related functions. This review analyses recent developments in the area of mitochondrial Ca(2+) signalling and attempts to summarize cell physiology aspects of the mitochondrial Ca(2+) transport machinery.
Advances in experimental medicine and biology 01/2012; 942:53-73. · 1.83 Impact Factor
[show abstract][hide abstract] ABSTRACT: Cell-penetrating peptides are short cationic peptides with the property of translocating across the plasma membrane and transferring macromolecules otherwise unable to permeate cell membranes. We investigated the potential ability of the protein transduction domain derived from amino acids 47-57 of the human immunodeficiency virus type 1 (HIV-1) TAT (transactivator of transcription) protein to be used as a nanocarrier for the delivery of aequorin, a Ca(2+)-sensitive photoprotein widely used as a reliable Ca(2+) reporter in cell populations. The TAT peptide, either covalently linked to apoaequorin or ionically bound to plasmids encoding differentially targeted aequorin, was supplied to plant suspension-cultured cells. The TAT-aequorin fusion protein was found to be rapidly and effectively translocated into plant cells. The chimeric molecule was internalized in fully active biological form and at levels suitable to monitor intracellular Ca(2+) concentrations. Plant cells incubated for just 5 min with TAT-aequorin responded to different environmental stimuli with the expected Ca(2+) signatures. On the other hand, TAT-mediated plasmid internalization did not provide the necessary level of transformation efficiency to allow calibration of luminescence signals into Ca(2+) concentration values. These results indicate that TAT-mediated aequorin transduction is a promising alternative to traditional plant transformation methods to monitor intracellular Ca(2+) dynamics rapidly and effectively in plant cells.
Plant and Cell Physiology 12/2011; 52(12):2225-35. · 4.13 Impact Factor
[show abstract][hide abstract] ABSTRACT: The inner ear converts sound waves into hearing signals through the mechanoelectrical transduction (MET) process. Deflection of the stereocilia bundle of hair cells causes the opening of channels that allow the entry of endolymph K(+) and Ca(2+). Ca(2+) that enters is crucial to the hearing process and is exported to the endolymph by the plasma membrane Ca(2+) pump (isoform PMCA2w/a): disturbances of the balance between Ca(2+) penetration and ejection, e.g. by pump mutations, generate deafness. Hearing loss caused by PMCA defects is frequently exacerbated by mutations in cadherin 23, a single pass stereociliar Ca(2+) binding protein that forms the tip links which permit the deflection of the stereocilia bundle and thus the opening of the MET channels. The PMCA2w/a pump ejects Ca(2+) to the endolymph even in the absence of the natural activator calmodulin. This satisfies the special Ca(2+) homeostasis requirements of the stereocilia/endolymph system. Here we have analyzed a mice and a human previously described pump mutant. The human mutant only exacerbated the deafness produced by a cadherin 23 mutation. The murine mutant overexpressed in model cells displayed an evident defect both in the basal activity of the pump and in the long range ejection of Ca(2+), the human mutant instead failed to impair the Ca(2+) ejection by the pump.
[show abstract][hide abstract] ABSTRACT: Activation by extracellular ligands of G protein-coupled (GPCRs) and tyrosine kinase receptors (RTKs), results in the generation of second messengers that in turn control specific cell functions. Further, modulation/amplification or inhibition of the initial signalling events, depend on the recruitment onto the plasma membrane of soluble protein effectors.High throughput methodologies to monitor quantitatively second messenger production, have been developed over the last years and are largely used to screen chemical libraries for drug development. On the contrary, no such high throughput methods are yet available for the other aspect of GPCRs regulation, i.e. protein translocation to the plasma membrane, despite the enormous interest of this phenomenon for the modulation of receptor downstream functions. Indeed, to date, the experimental procedures available are either inadequate or complex and expensive.
Here we describe the development of a novel conceptual approach to the study of cytosolic proteins translocation to the inner surface of the plasma membrane. The basis of the technique consists in: i) generating chimeras between the protein of interests and the calcium (Ca²⁺)-sensitive, luminescent photo-protein, aequorin and ii) taking advantage of the large Ca²⁺concentration [Ca²⁺] difference between bulk cytosolic and the sub-plasma membrane rim.
This approach, that keeps unaffected the translocation properties of the signalling protein, can in principle be applied to any protein that, upon activation, moves from the cytosol to the plasma membrane.Thus, not only the modulation of GPCRs and RTKs can be investigated in this way, but that of all other proteins that can be recruited to the plasma membrane also independently of receptor activation.Moreover, its automated version, which can provide information about the kinetics and concentration-dependence of the process, is also applicable to high throughput screening of drugs affecting the translocation process.
[show abstract][hide abstract] ABSTRACT: Parkinson's disease (PD) is a progressive neurodegenerative disease characterized by a loss of dopaminergic neurons in the substantia nigra pars compacta (SNPC) and the presence of intracytoplasmatic inclusions known as Lewy bodies, largely composed of alpha-synuclein (α-syn). PD is a multifactorial disease and its etiology remains largely elusive. Although more than 90% of the cases are sporadic, mutations in several nuclear encoded genes have been linked to the development of autosomal recessive and dominant familial parkinsonian syndromes (Bogaerts et al. (2008) Genes Brain Behav 7, 129-151), enhancing our understanding of biochemical and cellular mechanisms contributing to the disease. Many cellular mechanisms are thought to be involved in the dopaminergic neuronal death in PD, including oxidative stress, intracellular Ca(2+) homeostasis impairment, and mitochondrial dysfunctions. Furthermore, endoplasmic reticulum (ER) stress together with abnormal protein degradation by the ubiquitin proteasome system is considered to contribute to the PD pathogenesis. This review covers all the aspects related to the molecular mechanisms underlying the interplay between mitochondria, ER, and proteasome system in PD-associated neurodegeneration.
[show abstract][hide abstract] ABSTRACT: Calcium is an ambivalent signal: it is essential for the correct functioning of cell life, but may also become dangerous to it. The plasma membrane Ca(2+) ATPase (PMCA) and the plasma membrane Na(+)/Ca(2+) exchanger (NCX) are the two mechanisms responsible for Ca(2+) extrusion. The NCX has low Ca(2+) affinity but high capacity for Ca(2+) transport, whereas the PMCA has a high Ca(2+) affinity but low transport capacity for it. Thus, traditionally, the PMCA pump has been attributed a housekeeping role in maintaining cytosolic Ca(2+), and the NCX the dynamic role of counteracting large cytosolic Ca(2+) variations (especially in excitable cells). This view of the roles of the two Ca(2+) extrusion systems has been recently revised, as the specific functional properties of the numerous PMCA isoforms and splicing variants suggests that they may have evolved to cover both the basal Ca(2+) regulation (in the 100 nM range) and the Ca(2+) transients generated by cell stimulation (in the μM range).
Cold Spring Harbor perspectives in biology 01/2011; 3(2). · 9.63 Impact Factor
[show abstract][hide abstract] ABSTRACT: The mechanotransduction process in hair cells in the inner ear is associated with the influx of calcium from the endolymph. Calcium is exported back to the endolymph via the splice variant w/a of the PMCA2 of the stereocilia membrane. To further investigate the role of the pump, we have identified and characterized a novel ENU-induced mouse mutation, Tommy, in the PMCA2 gene. The mutation causes a non-conservative E629K change in the second intracellular loop of the pump that harbors the active site. Tommy mice show profound hearing impairment from P18, with significant differences in hearing thresholds between wild type and heterozygotes. Expression of mutant PMCA2 in CHO cells shows calcium extrusion impairment; specifically, the long term, non-stimulated calcium extrusion activity of the pump is inhibited. Calcium extrusion was investigated directly in neonatal organotypic cultures of the utricle sensory epithelium in Tommy mice. Confocal imaging combined with flash photolysis of caged calcium showed impairment of calcium export in both Tommy heterozygotes and homozygotes. Immunofluorescence studies of the organ of Corti in homozygous Tommy mice showed a progressive base to apex degeneration of hair cells after P40. Our results on the Tommy mutation along with previously observed interactions between cadherin-23 and PMCA2 mutations in mouse and humans underline the importance of maintaining the appropriate calcium concentrations in the endolymph to control the rigidity of cadherin and ensure the function of interstereocilia links, including tip links, of the stereocilia bundle.
Journal of Biological Chemistry 11/2010; 285(48):37693-703. · 4.65 Impact Factor