HDAC1/2-Dependent P0 Expression Maintains Paranodal and Nodal Integrity Independently of Myelin Stability through Interactions with Neurofascins.

The pathogenesis of peripheral neuropathies in adults is linked to maintenance mechanisms that are not well understood. Here, we elucidate a novel critical maintenance mechanism for Schwann cell (SC)-axon interaction. Using mouse genetics, ablation of the transcriptional regulators histone deacetylases 1 and 2 (HDAC1/2) in adult SCs severely affected paranodal and nodal integrity and led to demyelination/remyelination. Expression levels of the HDAC1/2 target gene myelin protein zero (P0) were reduced by half, accompanied by altered localization and stability of neurofascin (NFasc)155, NFasc186, and loss of Caspr and septate-like junctions. We identify P0 as a novel binding partner of NFasc155 and NFasc186, both in vivo and by in vitro adhesion assay. Furthermore, we demonstrate that HDAC1/2-dependent P0 expression is crucial for the maintenance of paranodal/nodal integrity and axonal function through interaction of P0 with neurofascins. In addition, we show that the latter mechanism is impaired by some P0 mutations that lead to late onset Charcot-Marie-Tooth disease.

The Gdap1 knockout mouse mechanistically links redox control to Charcot-Marie-Tooth disease.

The ganglioside-induced differentiation-associated protein 1 (GDAP1) is a mitochondrial fission factor and mutations in GDAP1 cause Charcot-Marie-Tooth disease. We found that Gdap1 knockout mice (Gdap1(-/-)), mimicking genetic alterations of patients suffering from severe forms of Charcot-Marie-Tooth disease, develop an age-related, hypomyelinating peripheral neuropathy. Ablation of Gdap1 expression in Schwann cells recapitulates this phenotype. Additionally, intra-axonal mitochondria of peripheral neurons are larger in Gdap1(-/-) mice and mitochondrial transport is impaired in cultured sensory neurons of Gdap1(-/-) mice compared with controls. These changes in mitochondrial morphology and dynamics also influence mitochondrial biogenesis. We demonstrate that mitochondrial DNA biogenesis and content is increased in the peripheral nervous system but not in the central nervous system of Gdap1(-/-) mice compared with control littermates. In search for a molecular mechanism we turned to the paralogue of GDAP1, GDAP1L1, which is mainly expressed in the unaffected central nervous system. GDAP1L1 responds to elevated levels of oxidized glutathione by translocating from the cytosol to mitochondria, where it inserts into the mitochondrial outer membrane. This translocation is necessary to substitute for loss of GDAP1 expression. Accordingly, more GDAP1L1 was associated with mitochondria in the spinal cord of aged Gdap1(-/-) mice compared with controls. Our findings demonstrate that Charcot-Marie-Tooth disease caused by mutations in GDAP1 leads to mild, persistent oxidative stress in the peripheral nervous system, which can be compensated by GDAP1L1 in the unaffected central nervous system. We conclude that members of the GDAP1 family are responsive and protective against stress associated with increased levels of oxidized glutathione.

Myelin is dependent on the Charcot-Marie-Tooth Type 4H disease culprit protein FRABIN/FGD4 in Schwann cells.

Studying the function and malfunction of genes and proteins associated with inherited forms of peripheral neuropathies has provided multiple clues to our understanding of myelinated nerves in health and disease. Here, we have generated a mouse model for the peripheral neuropathy Charcot-Marie-Tooth disease type 4H by constitutively disrupting the mouse orthologue of the suspected culprit gene FGD4 that encodes the small RhoGTPase Cdc42-guanine nucleotide exchange factor Frabin. Lack of Frabin/Fgd4 causes dysmyelination in mice in early peripheral nerve development, followed by profound myelin abnormalities and demyelination at later stages. At the age of 60 weeks, this was accompanied by electrophysiological deficits. By crossing mice carrying alleles of Frabin/Fgd4 flanked by loxP sequences with animals expressing Cre recombinase in a cell type-specific manner, we show that Schwann cell-autonomous Frabin/Fgd4 function is essential for proper myelination without detectable primary contributions from neurons. Deletion of Frabin/Fgd4 in Schwann cells of fully myelinated nerve fibres revealed that this protein is not only required for correct nerve development but also for accurate myelin maintenance. Moreover, we established that correct activation of Cdc42 is dependent on Frabin/Fgd4 function in healthy peripheral nerves. Genetic disruption of Cdc42 in Schwann cells of adult myelinated nerves resulted in myelin alterations similar to those observed in Frabin/Fgd4-deficient mice, indicating that Cdc42 and the Frabin/Fgd4-Cdc42 axis are critical for myelin homeostasis. In line with known regulatory roles of Cdc42, we found that Frabin/Fgd4 regulates Schwann cell endocytosis, a process that is increasingly recognized as a relevant mechanism in peripheral nerve pathophysiology. Taken together, our results indicate that regulation of Cdc42 by Frabin/Fgd4 in Schwann cells is critical for the structure and function of the peripheral nervous system. In particular, this regulatory link is continuously required in adult fully myelinated nerve fibres. Thus, mechanisms regulated by Frabin/Fgd4-Cdc42 are promising targets that can help to identify additional regulators of myelin development and homeostasis, which may crucially contribute also to malfunctions in different types of peripheral neuropathies.

LITAF (SIMPLE) regulates Wallerian degeneration after injury but is not essential for peripheral nerve development and maintenance: implications for Charcot-Marie-Tooth disease.

Missense mutations affecting the LITAF gene (also known as SIMPLE) lead to the dominantly inherited peripheral neuropathy Charcot-Marie-Tooth disease type 1C (CMT1C). In this study, we sought to determine the requirement of Litaf function in peripheral nerves, the only known affected tissue in CMT1C. We reasoned that this knowledge is a prerequisite for a thorough understanding of the underlying disease mechanism with regard to potential contributions by Litaf loss of function. In addition, we anticipated to obtain valuable information about the basic function of the Litaf protein in peripheral nerves. To address these issues, we generated mice without Litaf expression using gene disruption in embryonic stem cells and analyzed Litaf-deficient peripheral nerves during development, in maintenance, and after injury. Our results show that Litaf function is not absolutely required for peripheral nerve development and maintenance. In injured nerves, however, we found that lack of Litaf led to increased numbers of macrophages during Wallerian degeneration, accelerated myelin destruction, and the emergence of more axonal sprouts. Consistent with these data, the migration of Litaf-deficient macrophages was increased upon chemokine stimulation. We conclude that loss of Litaf function is unlikely to be a major contributor to CMT1C, but modulating effects of macrophages need to be considered in the etiology of the disease.

Foreign body granuloma due to Matridex injection for cosmetic purposes.

A new resorbable filler, Matridex, became commercially available during the last years with scarce evidence regarding side effects. A 43-year-old woman complained of multiple, painful, reddish, nonulcerated, hard nodules on both cheeks and periocular regions. Four weeks before, she had been injected by a general practitioner with Matridex for aesthetic purposes to correct wrinkles in the same areas of the nodular eruption. Histopathology showed a diffuse suppurative granulomatous reaction with the presence of multinucleate giant cells and many neutrophils involving the entire dermis. No areas of caseation were observed. The inflammatory granulomatous reaction surrounded 2 different types of nonpolarizing, bluish, exogenous material: one arranged in filamentous structures and the second composed by large spherical particles. All nodules were incised and drained; the patient received systemic antibiotic treatment for 2 consecutive weeks. The nodules progressively regressed and almost complete resolution was seen after 6 months. Matridex is a new resorbable filler constituted by a mixture of nonanimal-stabilized hyaluronic acid (HA), cross-linked HA, and dextranomer microspheres. Foreign body reactions have been described in association with other HA fillers, but a granulomatous reaction after the injection of Matridex has not been reported yet. Interestingly, in our patient, we were able to identify both fragments of HA: the filamentous particles and the spherical particles of dextranomer microspheres within the infiltrate, these last giving a characteristic and recognizable appearance to the histopathological picture.

The influence of sequence of impressions on children's anxiety and discomfort.

PURPOSE: Laboratory studies with adults and children have found lower pain reports when pain proceeds from high to low rather than from low to high. However, pediatric dentists often ease children into difficult procedures (from easiest to most difficult). This study investigated the influence of order during a clinical procedure that involved taking maxillary and mandibular alginate impressions. METHODS: Subjects were 24 children aged 5 to 6 years (preoperational stage) and 24 children aged 9 to 10 years (concrete operational stage). Children were randomly assigned to either start with the mandibular (presumed to be easier) or start with the maxillary (presumed to be harder) impressions. Discomfort during the sequence of impressions was measured using the "Affective Facial Scale." A telephone interview was conducted 2 weeks later to evaluate the memory of discomfort. RESULTS: The results indicated that the older children who started with the mandibular (easier) impression and ended with the maxillary (more uncomfortable) impression reported significantly lower discomfort than older children who started with the maxillary impression and ended with the mandibular (Mann-Whitney U, Z = -2.08; P < .037). The same tendency was noted 2 weeks later on a telephone interview. By phone, 92% of the older children who started with the mandibular impression rated the sequence of impressions as "not at all bad," while only 58% of the older children who started with the maxillary impression rated the overall experience as "not at all bad" (chi2 = 3.56, P < .059). The younger children did not show any significant difference in their ratings of discomfort at either of the assessment periods. CONCLUSIONS: Consistent with clinical practice, this study observed that older children benefit from beginning an appointment with an easier procedure and working up to a more difficult one.