Stephen C. Cannon

Muscle contraction depends on release of Ca(2+) from the sarcoplasmic reticulum (SR) and reuptake by the Ca(2+)adenosine triphosphatase SERCA. We discovered a putative muscle-specific long noncoding RNA that encodes a peptide of 34 amino acids and that we named dwarf open reading frame (DWORF). DWORF localizes to the SR membrane, where it enhances SERCA activity by displacing the SERCA inhibitors, phospholamban, sarcolipin, and myoregulin. In mice, overexpression of DWORF in cardiomyocytes increases peak Ca(2+) transient amplitude and SR Ca(2+) load while reducing the time constant of cytosolic Ca(2+) decay during each cycle of contraction-relaxation. Conversely, slow skeletal muscle lacking DWORF exhibits delayed Ca(2+) clearance and relaxation and reduced SERCA activity. DWORF is the only endogenous peptide known to activate the SERCA pump by physical interaction and provides a means for enhancing muscle contractility.

Eye movement were recorded from four juvenile rhesus monkeys (Macaca mulatta) before and after the injection of neurotoxins (kainate or ibotenate) in the region of the medial vestibular and prepositus hypoglossi nuclei, an area hypothesized to be the locus of the neural integrator for horizontal eye movement commands. Eye movements were measured in the head-restrained animal by the magnetic field/eye-coil method. The monkeys were trained to follow visual targets. A chamber implanted over a trephine hole in the skull permitted recordings to be made in the brain stem with metal microelectrodes. The abducens nuclei were located and used as a reference point for subsequent neurotoxin injections through cannulas. The effects of these lesions on fixation, vestibuloocular and optokinetic responses, and smooth pursuit were compared with predicted oculomotor anomalies caused by a loss of the neural integrator. Kainate and ibotenate did not create permanent lesions in this region of the brain stem. All the eye movements returned toward normal over the course of a few days to 2 wk. Histological examination revealed that the cannula tips were mainly located between the vestibular and prepositus hypoglossi nuclei, in their rostral 2 mm, bordered rostrally by the abducens nuclei. Dense gliosis clearly demarcated the cannula tracks, but for most injections there were no surrounding regions of neuronal loss. Thus the eye movement disorders were due to a reversible, not a permanent, lesion. The time constant for the neural integrator was determined from the velocity of the centripetal drift of the eyes just after an eccentric saccade in total darkness. For intact animals this time constant was greater than 20 s. Shortly after bilateral injections of neurotoxin, the time constant began to decrease and reached a minimum of 200 ms; every horizontal saccade was followed by a rapid centripetal drift with a time constant of approximately 200 ms. For vertical eye movements, in this acute phase, the time constant was approximately 2.5 s. The vestibuloocular reflex (VOR) was drastically changed by the lesions. A step of constant head velocity in total darkness evoked a step change in eye position rather than in velocity. In the absence of the neural integrator, the step velocity command from the canal afferents was not integrated to produce a ramp of eye position (normal slow phases); rather this signal was relayed directly to the motoneurons and caused a step in eye position. The per- and postrotatory decay of the head velocity signal was decreased to 5-6 s indicating that vestibular velocity storage was also impaired.(ABSTRACT TRUNCATED AT 400 WORDS)

Periodic paralyses (PPs) are rare inherited channelopathies that manifest as abnormal, often potassium (K)-sensitive, muscle membrane excitability leading to episodic flaccid paralysis. Hypokalaemic (HypoPP) and hyperkalaemic PP and Andersen-Tawil syndrome are genetically heterogeneous. Over the past decade mutations in genes encoding three ion channels, CACN1AS, SCN4A and KCNJ2, have been identified and account for at least 70% of the identified cases of PP and several allelic disorders. No prospective clinical studies have followed sufficiently large cohorts with characterized molecular lesions to draw precise conclusions. We summarize current knowledge of the clinical diagnosis, molecular genetics, genotype-phenotype correlations, pathophysiology and treatment in the PPs. We focus on unresolved issues including (i) Are there additional ion channel defects in cases without defined mutations? (ii) What is the mechanism for depolarization-induced weakness in Hypo PP? and finally (iii) Will detailed electrophysiological studies be able to correctly identify specific channel mutations? Understanding the pathophysiology of the potassium-sensitive PPs ought to reduce genetic complexity, allow subjects to be stratified during future clinical trials and increase the likelihood of observing true clinical effects. Ideally, therapy for the PPs will prevent attacks, avoid permanent weakness and improve quality of life. Moreover, understanding the skeletal muscle channelopathies will hopefully lead to insights into the more common central nervous system channel diseases such as migraine and epilepsy.

Chondroitin sulfate proteoglycans (CSPGs) are a family of extracellular matrix molecules with various functions in regulating tissue morphogenesis, cell division, and axon guidance. A number of CSPGs are highly upregulated by reactive glial scar tissues after injuries and form a strong barrier for axonal regeneration in the adult vertebrate CNS. Although CSPGs may negatively regulate axonal growth via binding and altering activity of other growth-regulating factors, the molecular mechanisms by which CSPGs restrict axonal elongation are not well understood. Here, we identified a novel receptor mechanism whereby CSPGs inhibit axonal growth via interactions with neuronal transmembrane leukocyte common antigen-related phosphatase (LAR). CSPGs bind LAR with high affinity in transfected COS-7 cells and coimmunoprecipitate with LAR expressed in various tissues including the brain and spinal cord. CSPG stimulation enhances activity of LAR phosphatase in vitro. Deletion of LAR in knock-out mice or blockade of LAR with sequence-selective peptides significantly overcomes neurite growth restrictions of CSPGs in neuronal cultures. Intracellularly, CSPG-LAR interaction mediates axonal growth inhibition of neurons partially via inactivating Akt and activating RhoA signals. Systemic treatments with LAR-targeting peptides in mice with thoracic spinal cord transection injuries induce significant axon growth of descending serotonergic fibers in the vicinity of the lesion and beyond in the caudal spinal cord and promote locomotor functional recovery. Identification of LAR as a novel CSPG functional receptor provides a therapeutic basis for enhancing axonal regeneration and functional recovery after CNS injuries in adult mammals.