CRMP4-mediated fornix development involves semaphorin-3E signaling pathway

Neurodevelopmental axonal pathfinding plays a central role in correct brain wiring and subsequent cognitive abilities. Within the growth cone, various intracellular effectors transduce axonal guidance signals by remodeling the cytoskeleton. Semaphorin-3E (Sema3E) is a guidance cue implicated in development of the fornix, a neuronal tract connecting the hippocampus to the hypothalamus. Microtubule-Associated Protein 6 (MAP6) has been shown to be involved in the Sema3E growth-promoting signaling pathway. In this study, we identified the Collapsin Response Mediator Protein 4 (CRMP4) as a MAP6 partner and a crucial effector in Sema3E growth-promoting activity. CRMP4-KO mice displayed abnormal fornix development reminiscent of that observed in Sema3E-KO mice. CRMP4 was shown to interact with the Sema3E tripartite receptor complex within Detergent-Resistant Membrane (DRM) domains, and DRM domain integrity was required to transduce Sema3E signaling through the Akt/GSK3 pathway. Finally, we showed that the cytoskeleton-binding domain of CRMP4 is required for Sema3E's growth-promoting activity, suggesting that CRMP4 plays a role at the interface between Sema3E receptors, located in DRM domains, and the cytoskeleton network. As the fornix is affected in many psychiatric diseases, such as schizophrenia, our results provide new insights to better understand the neurodevelopmental components of these diseases.

Ascending Painful Paresthesias, Progressive Ataxia, and Bilateral Foot Drop

A 63-year-old woman had development of ascending paresthesias with lancinating and stabbing pain in all extremities. The symptoms began asymmetrically in the left leg and progressed to involve the right leg and both hands. She noticed progressive bilateral leg weakness, gait instability, and new numbness in the left middle back. She had recurrent falls and required the use of a cane and eventually a walker. She had 18.2 kg of weight loss. She had no autonomic symptoms or bladder or bowel dysfunction. Examination 1 year after symptom onset showed an emaciated, ill-appearing woman. On neurologic examination, she had marked gait ataxia with profound proprioceptive loss in all extremities, asymmetrically reduced pinprick sensation distal to the left thigh, right knee, and both forearms, as well as bilateral middle thoracic dermatomes. She had bilateral foot drop and mild weakness in bilateral hamstring and intrinsic hand muscles. Her deep tendon reflexes were globally absent. Toes were mute to plantar stimulation. Magnetic resonance imaging of the entire spine demonstrated subtle increased T2 signal in the posterior columns extending along cervical and thoracic segments and patchy gadolinium enhancement of the cervical and lumbosacral nerve roots. Electrodiagnostic testing demonstrated a length-dependent axonal sensorimotor peripheral neuropathy. Cerebrospinal fluid analysis showed an increased protein concentration, 9 cerebrospinal fluid-restricted oligoclonal bands, increased immunoglobulin G index and synthesis rate, and normal blood cell count. Paraneoplastic antibody evaluation showed high titers of collapsin-response mediator protein 5-immunoglobulin G autoantibodies in the serum and cerebrospinal fluid. Whole-body 18F-fludeoxyglucose–positron emission tomography indicated multiple hypermetabolic mediastinal and hilar lymph nodes. Biopsy of a mediastinal lymph node was consistent with small cell lung carcinoma. The patient was diagnosed with collapsin-response mediator protein 5- immunoglobulin G paraneoplastic myeloneuropathy associated with small cell carcinoma of the lung. The patient received a trial of intravenous methylprednisolone followed by chemotherapy, along with chest and prophylactic brain radiotherapy. She achieved a short period of clinical stabilization and mild improvement in gait and limb ataxia. Subsequently, her ataxia and bilateral leg weakness worsened. Her clinical condition rapidly deteriorated, and she became severely malnourished and bedridden, dying 12 weeks later, 2 years after symptom onset. Collapsin-response mediator protein 5- immunoglobulin G antibodies have been associated with asymmetric, painful polyradiculoneuropathy with coexisting myelopathy, often in the setting of thymoma or small cell lung cancer.

Fatigue, Blurry Vision, and Swollen Optic Nerves

A 71-year-old woman had development of generalized fatigue over 1 week, along with low-grade fever. The fever resolved, but the fatigue persisted. Subsequently, retro-orbital and head discomfort developed. One month later, she had blurred vision. An ophthalmic examination revealed mild dyschromatopsia, bilateral visual field constriction, bilateral marked optic disc edema, and vitreous cells graded as vitreous haze score 2.0. Magnetic resonance imaging of the brain showed confluent abnormal areas of T2 hyperintensity without mass effect or enhancement involving the subcortical and periventricular white matter in the cerebral hemispheres bilaterally, basal ganglia, pons, and left thalamus. She had 2 lumbar punctures, which showed normal opening pressures. Cerebrospinal fluid analysis showed an increased white blood cell count cytologically consistent with reactive pleocytosis with a predominance of lymphocytes. The cerebrospinal fluid protein level was increased and cultures were negative for organisms. Immunostain confirmed polyclonal plasma cells and a possible T-cell proliferative disorder. The cerebrospinal fluid and serum were positive for collapsin-response mediator protein 5-immunoglobulin G and microtubule-associated protein 1B- immunoglobulin G antibodies at high titers. Computed tomography of the chest, abdomen, and pelvis showed an indeterminate pulmonary nodule in the upper lobe. Bronchoscopy identified thickened mucosa in the right lower lung consistent with small cell carcinoma. Positron emission tomography showed abnormal hypermetabolic areas of the ascending colon. Biopsy revealed tubulovillous adenoma of the ascending colon, and the patient underwent a right-sided colon resection and anastomosis. The patient was diagnosed with paraneoplastic optic neuropathy (collapsin-response mediator protein 5-immunoglobulin G–associated optic neuropathy and vitritis). Intravenous methylprednisolone was given for 5 days, followed by a prolonged course of oral prednisone, with slight visual improvement. The patient underwent a right-sided thoracotomy with biopsy of the right lower lobe, the results of which were consistent with small cell undifferentiated carcinoma. Paraneoplastic neurologic syndromes are a heterogeneous group of disorders associated with various systemic cancers and with other mechanisms believed to be immune mediated. Paraneoplastic visual syndromes can precede or follow a diagnosis of cancer.

CRMP2 Is Involved in Regulation of Mitochondrial Morphology and Motility in Neurons

Regulation of mitochondrial morphology and motility is critical for neurons, but the exact mechanisms are unclear. Here, we demonstrate that these mechanisms may involve collapsin response mediator protein 2 (CRMP2). CRMP2 is attached to neuronal mitochondria and binds to dynamin-related protein 1 (Drp1), Miro 2, and Kinesin 1 light chain (KLC1). Treating neurons with okadaic acid (OA), an inhibitor of phosphatases PP1 and PP2A, resulted in increased CRMP2 phosphorylation at Thr509/514, Ser522, and Thr555, and augmented Drp1 phosphorylation at Ser616. The CRMP2-binding small molecule (S)-lacosamide ((S)-LCM) prevented an OA-induced increase in CRMP2 phosphorylation at Thr509/514 and Ser522 but not at Thr555, and also failed to alleviate Drp1 phosphorylation. The increased CRMP2 phosphorylation correlated with decreased CRMP2 binding to Drp1, Miro 2, and KLC1. (S)-LCM rescued CRMP2 binding to Drp1 and Miro 2 but not to KLC1. In parallel with CRMP2 hyperphosphorylation, OA increased mitochondrial fission and suppressed mitochondrial traffic. (S)-LCM prevented OA-induced alterations in mitochondrial morphology and motility. Deletion of CRMP2 with a small interfering RNA (siRNA) resulted in increased mitochondrial fission and diminished mitochondrial traffic. Overall, our data suggest that the CRMP2 expression level and phosphorylation state are involved in regulating mitochondrial morphology and motility in neurons.

Clinical evidence that a dysregulated master neural network modulator may aid in diagnosing schizophrenia

There are no validated biomarkers for schizophrenia (SCZ), a disorder linked to neural network dysfunction. We demonstrate that collapsin response mediator protein-2 (CRMP2), a master regulator of cytoskeleton and, hence, neural circuitry, may form the basis for a biomarker because its activity is uniquely imbalanced in SCZ patients. CRMP2’s activity depends upon its phosphorylation state. While an equilibrium between inactive (phosphorylated) and active (nonphosphorylated) CRMP2 is present in unaffected individuals, we show that SCZ patients are characterized by excess active CRMP2. We examined CRMP2 levels first in postmortem brains (correlated with neuronal morphometrics) and then, because CRMP2 is expressed in lymphocytes as well, in the peripheral blood of SCZ patients versus age-matched unaffected controls. In the brains and, more starkly, in the lymphocytes of SCZ patients <40 y old, we observed that nonphosphorylated CRMP2 was higher than in controls, while phosphorylated CRMP2 remained unchanged from control. In the brain, these changes were associated with dendritic structural abnormalities. The abundance of active CRMP2 with insufficient opposing inactive p-CRMP2 yielded a unique lowering of the p-CRMP2:CRMP2 ratio in SCZ patients, implying a disruption in the normal equilibrium between active and inactive CRMP2. These clinical data suggest that measuring CRMP2 and p-CRMP2 in peripheral blood might reflect intracerebral processes and suggest a rapid, minimally invasive, sensitive, and specific adjunctive diagnostic aid for early SCZ: increased CRMP2 or a decreased p-CRMP2:CRMP2 ratio may help cinch the diagnosis in a newly presenting young patient suspected of SCZ (versus such mimics as mania in bipolar disorder, where the ratio is high).

Spastin interacts with CRMP5 to promote spindle organization in mouse oocytes by severing microtubules

Microtubule-severing protein (MTSP) is critical for the survival of both mitotic and postmitotic cells. However, the study of MTSP during meiosis of mammalian oocytes has not been reported. We found that spastin, a member of the MTSP family, was highly expressed in oocytes and aggregated in spindle microtubules. After knocking down spastin by specific siRNA, the spindle microtubule density of meiotic oocytes decreased significantly. When the oocytes were cultured in vitro, the oocytes lacking spastin showed an obvious maturation disorder. Considering the microtubule-severing activity of spastin, we speculate that spastin on spindles may increase the number of microtubule broken ends by severing the microtubules, therefore playing a nucleating role, promoting spindle assembly and ensuring normal meiosis. In addition, we found the colocalization and interaction of collapsin response mediator protein 5 (CRMP5) and spastin in oocytes. CRMP5 can provide structural support and promote microtubule aggregation, creating transportation routes, and can interact with spastin in the microtubule activity of nerve cells (30). Knocking down CRMP5 may lead to spindle abnormalities and developmental disorders in oocytes. Overexpression of spastin may reverse the abnormal phenotype caused by the deletion of CRMP5. In summary, our data support a model in which the interaction between spastin and CRMP5 promotes the assembly of spindle microtubules in oocytes by controlling microtubule dynamics, therefore ensuring normal meiosis.