Muscle-Derived Extracellular Signal-Regulated Kinases 1 and 2 Are Required for the Maintenance of Adult Myofibers and Their Neuromuscular Junctions

The Ras–extracellular signal-regulated kinase 1 and 2 (ERK1/2) pathway appears to be important for the development, maintenance, aging, and pathology of mammalian skeletal muscle. Yet no gene targeting of Erk1/2 in muscle fibers in vivo has been reported to date. We combined a germ line Erk1 mutation with Cre-loxP Erk2 inactivation in skeletal muscle to produce, for the first time, mice lacking ERK1/2 selectively in skeletal myofibers. Animals lacking muscle ERK1/2 displayed stunted postnatal growth, muscle weakness, and a shorter life span. Their muscles examined in this study, sternomastoid and tibialis anterior, displayed fragmented neuromuscular synapses and a mixture of modest fiber atrophy and loss but failed to show major changes in fiber type composition or absence of cell surface dystrophin. Whereas the lack of only ERK1 had no effects on the phenotypes studied, the lack of myofiber ERK2 explained synaptic fragmentation in the sternomastoid but not the tibialis anterior and a decrease in the expression of the acetylcholine receptor (AChR) epsilon subunit gene mRNA in both muscles. A reduction in AChR protein was documented in line with the above mRNA results. Evidence of partial denervation was found in the sternomastoid but not the tibialis anterior. Thus, myofiber ERK1/2 are differentially required for the maintenance of myofibers and neuromuscular synapses in adult mice.     

Muscles in a mouse model of spinal muscular atrophy show profound defects in neuromuscular development even in the absence of failure in neuromuscular transmission or loss of motor neurons

A mouse model of the devastating human disease "spinal muscular atrophy" (SMA) was used to investigate the severe muscle weakness and spasticity that precede the death of these animals near the end of the 2nd postnatal week. Counts of motor units to the soleus muscle as well as of axons in the soleus muscle nerve showed no loss of motor neurons. Similarly, neither immunostaining of neuromuscular junctions nor the measurement of the tension generated by nerve stimulation gave evidence of any significant impairment in neuromuscular transmission, even when animals were maintained up to 5days longer via a supplementary diet. However, the muscles were clearly weaker, generating less than half their normal tension. Weakness in 3 muscles examined in the study appears due to a severe but uniform reduction in muscle fiber size. The size reduction results from a failure of muscle fibers to grow during early postnatal development and, in soleus, to a reduction in number of fibers generated. Neuromuscular development is severely delayed in these mutant animals: expression of myosin heavy chain isoforms, the elimination of polyneuronal innervation, the maturation in the shape of the AChR plaque, the arrival of SCs at the junctions and their coverage of the nerve terminal, the development of junctional folds. Thus, if SMA in this particular mouse is a disease of motor neurons, it can act in a manner that does not result in their death or disconnection from their targets but nonetheless alters many aspects of neuromuscular development.     

A unique point mutation in the PMP22 gene is associated with Charcot-Marie-Tooth disease and deafness.

Charcot-Marie-Tooth disease (CMT) with deafness is clinically distinct among the genetically heterogeneous group of CMT disorders. Molecular studies in a large family with autosomal dominant CMT and deafness have not been reported. The present molecular study involves a family with progressive features of CMT and deafness, originally reported by Kousseff et al. Genetic analysis of 70 individuals (31 affected, 28 unaffected, and 11 spouses) revealed linkage to markers on chromosome 17p11.2-p12, with a maximum LOD score of 9.01 for marker D17S1357 at a recombination fraction of .03. Haplotype analysis placed the CMT-deafness locus between markers D17S839 and D17S122, a approximately 0.6-Mb interval. This critical region lies within the CMT type 1A duplication region and excludes MYO15, a gene coding an unconventional myosin that causes a form of autosomal recessive deafness called DFNB3. Affected individuals from this family do not have the common 1.5-Mb duplication of CMT type 1A. Direct sequencing of the candidate peripheral myelin protein 22 (PMP22) gene detected a unique G-->C transversion in the heterozygous state in all affected individuals, at position 248 in coding exon 3, predicted to result in an Ala67Pro substitution in the second transmembrane domain of PMP22.     

Modulation of Agrin-induced Acetylcholine Receptor Clustering by Extracellular Signal-regulated Kinases 1 and 2 in Cultured Myotubes

Agrin released by motoneurons induces and/or maintains acetylcholine receptor (AChR) clustering and other aspects of postsynaptic differentiation at the vertebrate neuromuscular junction. Agrin acts by binding and activating a receptor complex containing LDL receptor protein 4 (Lrp4) and muscle-specific kinase (MuSK). Two critical downstream components of this signaling cascade, Dox-7 and rapsyn, have been identified. However, additional intracellular essential elements remain unknown. Prior observations by others and us suggested antagonistic interactions between agrin and neuregulin-1 (Nrg-1) signaling in cultured myotubes and developing muscle fibers in vivo. A hallmark of Nrg-1 signaling in skeletal muscle cells is the activation of extracellular signal-regulated kinases 1 and 2 (ERK1/2). ERK1/2 are also activated in most cells by phorbol 12-myristate 13-acetate, a classical inhibitor of agrin-induced AChR clustering in myotubes. Here, it was investigated whether agrin activates ERK1/2 directly and whether such activation modulates agrin-induced AChR clustering. Agrin induced a rapid but transient activation of ERK1/2 in myotubes that was Lrp4/MuSK-dependent. However, blocking this ERK1/2 activation did not prevent but potentiated AChR clustering induced by agrin. ERK1/2 activation was dispensable for Nrg-1-mediated inhibition of the AChR clustering activity of agrin, but was indispensable for such activity by phorbol 12-myristate 13-acetate. Together, these results suggest agrin-induced activation of ERK1/2 is a negative modulator of agrin signaling in skeletal muscle cells.     

Pre-counseling education materials for BRCA testing: does tailoring make a difference?

Although tailored print materials (TPMs) have been assessed for a variety of behavioral targets, their effectiveness as decision aids for genetic testing had not been evaluated at the time this study began. We compared TPMs and non-tailored print material (NPMs) that included similar content about genetic testing for breast and ovarian cancer susceptibility. TPMs were prepared especially for an individual based on information from and about her. We mailed baseline surveys to 461 women referred by physicians or identified through a tumor registry. All had personal and family histories of breast and/or ovarian cancer and, on the basis of these histories, an estimated > or =10% probability of carrying a mutation in the breast/ovarian cancer genes BRCA1 or BRCA2. The 325 (70%) who responded were randomly assigned to receive TPM or NPM. Followup surveys, mailed 2 weeks following receipt of print materials, were returned by 262 women (81% of baseline responders). Participants were predominately white (94%) and well-educated (50% college graduates). The mean age was 49 years. At follow-up, TPM recipients exhibited significantly greater improvement in percent of correct responses for the 13-item true/false measure of knowledge (24% increase for TPM vs. 16% for NPM; p < 0.0001) and significantly less over-estimation of risk of being a mutation carrier (40% TPM group overestimated vs. 70% NPM; p < 0.0001). Anxiety did not differ significantly between groups. Reactions to materials differed on two items: "seemed to be prepared just for me" (76% TPM vs. 52% NPM; p < 0.001) and "told me what I wanted to know about BRCA1 and 2 testing" (98% TPM vs. 91% NPM; p < 0.05). TPMs showed an advantage in increasing knowledge and enhancing accuracy of perceived risk. Both are critical components of informed decision making.     

Factors associated with annual-interval mammography for women in their 40s

Background: Evidence is mounting that annual mammography for women in their 40s may be the optimal schedule to reduce morbidity and mortality from breast cancer. Few studies have assessed predictors of repeat mammography on an annual interval among these women. Methods: We assessed mammography screening status among 596 insured Black and Non-Hispanic white women ages 43–49. Adherence was defined as having a second mammogram 10–14 months after a previous mammogram. We examined socio-demographic, medical and healthcare-related variables on receipt of annual-interval repeat mammograms. We also assessed barriers associated with screening. Results: 44.8% of the sample were adherent to annual-interval mammography. A history of self-reported abnormal mammograms, family history of breast cancer and never having smoked were associated with adherence. Saying they had not received mammography reminders and reporting barriers to mammography were associated with non-adherence. Four barrier categories were associated with women's non-adherence: lack of knowledge/not thinking mammograms are needed, cost, being too busy, and forgetting to make/keep appointments. Conclusions: Barriers we identified are similar to those found in other studies. Health professionals may need to take extra care in discussing mammography screening risk and benefits due to ambiguity about screening guidelines for women in their 40s, especially for women without family histories of breast cancer or histories of abnormal mammograms. Reminders are important in promoting mammography and should be coupled with other strategies to help women maintain adherence to regular mammography.