CamKII inhibitors reduce mitotic instability, connexon anomalies and progression of the in vivo behavioral phenotype in transgenic animals expressing a mutated Gjb1 gene

Calcium Regulation of Connexin Hemichannels

Connexin hemichannels (HCs) expressed at the plasma membrane of mammalian cells are of paramount importance for intercellular communication. In physiological conditions, HCs can form gap junction (GJ) channels, providing a direct diffusive path between neighbouring cells. In addition, unpaired HCs provide conduits for the exchange of solutes between the cytoplasm and the extracellular milieu, including messenger molecules involved in paracrine signalling. The synergistic action of membrane potential and Ca2+ ions controls the gating of the large and relatively unselective pore of connexin HCs. The four orders of magnitude difference in gating sensitivity to the extracellular ([Ca2+]e) and the cytosolic ([Ca2+]c) Ca2+ concentrations suggests that at least two different Ca2+ sensors may exist. While [Ca2+]e acts as a spatial modulator of the HC opening, which is most likely dependent on the cell layer, compartment, and organ, [Ca2+]c triggers HC opening and the release of extracellular bursts of messenger molecules. Such molecules include ATP, cAMP, glutamate, NAD+, glutathione, D-serine, and prostaglandins. Lost or abnormal HC regulation by Ca2+ has been associated with several diseases, including deafness, keratitis ichthyosis, palmoplantar keratoderma, Charcot-Marie-Tooth neuropathy, oculodentodigital dysplasia, and congenital cataracts. The fact that both an increased and a decreased Ca2+ sensitivity has been linked to pathological conditions suggests that Ca2+ in healthy cells finely tunes the normal HC function. Overall, further investigation is needed to clarify the structural and chemical modifications of connexin HCs during [Ca2+]e and [Ca2+]c variations. A molecular model that accounts for changes in both Ca2+ and the transmembrane voltage will undoubtedly enhance our interpretation of the experimental results and pave the way for developing therapeutic compounds targeting specific HC dysfunctions.

Mechanisms and Treatments in Demyelinating CMT

Demyelinating forms of Charcot-Marie-Tooth disease (CMT) are genetically and phenotypically heterogeneous and result from highly diverse biological mechanisms including gain of function (including dominant negative effects) and loss of function. While no definitive treatment is currently available, rapid advances in defining the pathomechanisms of demyelinating CMT have led to promising pre-clinical studies, as well as emerging clinical trials. Especially promising are the recently completed pre-clinical genetic therapy studies in PMP-22, GJB1, and SH3TC2-associated neuropathies, particularly given the success of similar approaches in humans with spinal muscular atrophy and transthyretin familial polyneuropathy. This article focuses on neuropathies related to mutations in PMP-22, MPZ, and GJB1, which together comprise the most common forms of demyelinating CMT, as well as on select rarer forms for which promising treatment targets have been identified. Clinical characteristics and pathomechanisms are reviewed in detail, with emphasis on therapeutically targetable biological pathways. Also discussed are the challenges facing the CMT research community in its efforts to advance the rapidly evolving biological insights to effective clinical trials. These considerations include the limitations of currently available animal models, the need for personalized medicine approaches/allele-specific interventions for select forms of demyelinating CMT, and the increasing demand for optimal clinical outcome assessments and objective biomarkers.

Animal Models as a Tool to Design Therapeutical Strategies for CMT-like Hereditary Neuropathies

Since ancient times, animal models have provided fundamental information in medical knowledge. This also applies for discoveries in the field of inherited peripheral neuropathies (IPNs), where they have been instrumental for our understanding of nerve development, pathogenesis of neuropathy, molecules and pathways involved and to design potential therapies. In this review, we briefly describe how animal models have been used in ancient medicine until the use of rodents as the prevalent model in present times. We then travel along different examples of how rodents have been used to improve our understanding of IPNs. We do not intend to describe all discoveries and animal models developed for IPNs, but just to touch on a few arbitrary and paradigmatic examples, taken from our direct experience or from literature. The idea is to show how strategies have been developed to finally arrive to possible treatments for IPNs.

Therapeutic Development in Charcot Marie Tooth Type 1 Disease

Charcot–Marie–Tooth disease (CMT) is the most frequent hereditary peripheral neuropathies. It is subdivided in two main groups, demyelinating (CMT1) and axonal (CMT2). CMT1 forms are the most frequent. The goal of this review is to present published data on 1—cellular and animal models having opened new potential therapeutic approaches. 2—exploration of these tracks, including clinical trials. The first conclusion is the great increase of publications on CMT1 subtypes since 2000. We discussed two points that should be considered in the therapeutic development toward a regulatory-approved therapy to be proposed to patients. The first point concerns long term safety if treatments will be a long-term process. The second point relates to the evaluation of treatment efficiency. Degradation of CMT clinical phenotype is not linear and progressive.

Interplay Between Calcium and AMPK Signaling in Human Cytomegalovirus Infection

Calcium signaling and the AMP-activated protein kinase (AMPK) signaling networks broadly regulate numerous aspects of cell biology. Human Cytomegalovirus (HCMV) infection has been found to actively manipulate the calcium-AMPK signaling axis to support infection. Many HCMV genes have been linked to modulating calcium signaling, and HCMV infection has been found to be reliant on calcium signaling and AMPK activation. Here, we focus on the cell biology of calcium and AMPK signaling and what is currently known about how HCMV modulates these pathways to support HCMV infection and potentially contribute to oncomodulation.

Charcot-Marie-Tooth: From Molecules to Therapy

Charcot-Marie-Tooth (CMT) is the most prevalent category of inherited neuropathy. The most common inheritance pattern is autosomal dominant, though there also are X-linked and autosomal recessive subtypes. In addition to a variety of inheritance patterns, there are a myriad of genes associated with CMT, reflecting the heterogeneity of this disorder. Next generation sequencing (NGS) has expanded and simplified the diagnostic yield of genes/molecules underlying and/or associated with CMT, which is of paramount importance in providing a substrate for current and future targeted disease-modifying treatment options. Considerable research attention for disease-modifying therapy has been geared towards the most commonly encountered genetic mutations (PMP22, GJB1, MPZ, and MFN2). In this review, we highlight the clinical background, molecular understanding, and therapeutic investigations of these CMT subtypes, while also discussing therapeutic research pertinent to the remaining less common CMT subtypes.

What's the Function of Connexin 32 in the Peripheral Nervous System?

Connexin 32 (Cx32) is a fundamental protein in the peripheral nervous system (PNS) as its mutations cause the X-linked form of Charcot–Marie–Tooth disease (CMT1X), the second most common form of hereditary motor and sensory neuropathy and a demyelinating disease for which there is no effective therapy. Since mutations of the GJB1 gene encoding Cx32 were first reported in 1993, over 450 different mutations associated with CMT1X including missense, frameshift, deletion and non-sense ones have been identified. Despite the availability of a sizable number of studies focusing on normal and mutated Cx32 channel properties, the crucial role played by Cx32 in the PNS has not yet been elucidated, as well as the molecular pathogenesis of CMT1X. Is Cx32 fundamental during a particular phase of Schwann cell (SC) life? Are Cx32 paired (gap junction, GJ) channels in myelinated SCs important for peripheral nerve homeostasis? The attractive hypothesis that short coupling of adjacent myelin layers by Cx32 GJs is required for efficient diffusion of K⁺ and signaling molecules is still debated, while a growing body of evidence is supporting other possible functions of Cx32 in the PNS, mainly related to Cx32 unpaired channels (hemichannels), which could be involved in a purinergic-dependent pathway controlling myelination. Here we review the intriguing puzzle of findings about Cx32 function and dysfunction, discussing possible directions for future investigation.

CMTX1 patients' cells present genomic instability corrected by CamKII inhibitors

BACKGROUND

We previously described that fibroblasts from animal models of CMTX1 present genomic instability and poor connexon activity. In vivo, these transgenic mice present motor deficits. This phenotype could be significantly reverted by treatment with (CamKII) inhibitors. The objective of this study is to translate our findings to patients.

METHODS

We cultured fibroblasts from skin biopsies of CMTX1 patients and analyzed cells for genomic instabilty, connexon activity, and potential correction by CamKII inhibitors.

RESULTS

The phenotypic analysis of these cells confirmed strong similarities between the GJB1 transgenic mouse cell lines and CMTX1 patient fibroblast cell lines. Both present mitotic anomalies, centrosome overduplication, and connexon activity deficit. This phenotype is corrected by CamKII inhibitors.

CONCLUSIONS

Our data demonstrate that fibroblasts from CMTX1 patients present a phenotype similar to transgenic lines that can be corrected by CamKII inhibitors. This presents a track to develop therapeutic strategies for CMTX1 treatment.