Sarina B. Elmariah

Astrocytes Regulate Inhibitory Synapse Formation via Trk-Mediated Modulation of Postsynaptic GABAA Receptors

Astrocytes promote the formation and function of excitatory synapses in the CNS. However, whether and how astrocytes modulate inhibitory synaptogenesis are essentially unknown. We asked whether astrocytes regulate the formation of inhibitory synapses between hippocampal neurons during maturation in vitro. Neuronal coculture with astrocytes or treatment with astrocyte-conditioned medium (ACM) increased the number of inhibitory presynaptic terminals, the frequency of miniature IPSCs, and the number and synaptic localization of GABAA receptor (GABAAR) clusters during the first 10 d in vitro. We asked whether neurotrophins, which are potent modulators of inhibitory synaptic structure and function, mediate the effects of astrocytes on inhibitory synapses. ACM from BDNF- or tyrosine receptor kinase B (TrkB)-deficient astrocytes increased inhibitory presynaptic terminals and postsynaptic GABAAR clusters in wild-type neurons, suggesting that BDNF and TrkB expression in astrocytes is not required for these effects. In contrast, although the increase in the number of inhibitory presynaptic terminals persisted, no increase was observed in postsynaptic GABAAR clusters after ACM treatment of hippocampal neurons lacking BDNF or TrkB. These results suggest that neurons, not astrocytes, are the relevant source of BDNF and are the site of TrkB activation required for postsynaptic GABAAR modulation. These data also suggest that astrocytes may modulate postsynaptic development indirectly by stimulating Trk signaling between neurons. Together, these data show that astrocytes modulate inhibitory synapse formation via distinct presynaptic and postsynaptic mechanisms.

Postsynaptic TrkB-Mediated Signaling Modulates Excitatory and Inhibitory Neurotransmitter Receptor Clustering at Hippocampal Synapses

Tyrosine receptor kinase B (TrkB)-mediated signaling modulates synaptic structure and strength in hippocampal and other neurons, but the underlying mechanisms are poorly understood. Full-length and truncated TrkB are diffusely distributed throughout the dendrites and soma of rat hippocampal neurons grown in vitro. Manipulation of TrkB-mediated signaling resulted in dramatic changes in the number and synaptic localization of postsynaptic NMDA receptor (NMDAR) and GABAA receptor (GABAAR) clusters. BDNF treatment resulted in an increase in the number of NMDAR and GABAAR clusters and increased the proportion of clusters apposed to presynaptic terminals. Downregulation of TrkB signaling resulted in a decrease in receptor cluster number and synaptic localization. Examination of the time course of the effects of BDNF on receptor clusters showed that the increase in GABAAR clusters preceded the increase in NMDAR clusters by at least 12 hr. Moreover, the TrkB-mediated effects on NMDAR clusters were dependent on GABAAR activation. Although TTX, APV, and CNQX treatment had no effect, blockade of GABAARs with bicuculline abolished the BDNF-mediated increase in NMDAR cluster number and synaptic localization. In contrast, application of exogenous GABA prevented the decrease in NMDAR clusters induced by BDNF scavenging. Together, these results suggest that TrkB-mediated signaling modulates the clustering of postsynaptic GABAARs and that receptor activity is required for a subsequent upregulation of NMDAR clusters. Therefore, TrkB-mediated effects on postsynaptic neurotransmitter clusters may be part of a mechanism that balances inhibitory and excitatory synaptic transmission in developing neural circuits.

Astrocyte secreted proteins selectively increase hippocampal GABAergic axon length, branching, and synaptogenesis

Astrocytes modulate the formation and function of glutamatergic synapses in the CNS, but whether astrocytes modulate GABAergic synaptogenesis is unknown. We demonstrate that media conditioned by astrocytes, but not other cells, enhanced GABAergic but not glutamatergic axon length and branching, and increased the number and density of presynaptically active GABAergic synapses in dissociated hippocampal cultures. Candidate mechanisms and factors, such as activity, neurotrophins, and cholesterol were excluded as mediating these effects. While thrombospondins secreted by astrocytes are necessary and sufficient to increase hippocampal glutamatergic synaptogenesis, they do not mediate astrocyte effects on GABAergic synaptogenesis. We show that the factors in astrocyte conditioned media that selectively affect GABAergic neurons are proteins. Taken together, our results show that astrocytes increase glutamatergic and GABAergic synaptogenesis via different mechanisms and release one or more proteins with the novel functions of increasing GABAergic axon length, branching and synaptogenesis.

Neurotrophin signaling among neurons and glia during formation of tripartite synapses

Synapse formation in the CNS is a complex process that involves the dynamic interplay of numerous signals exchanged between pre- and postsynaptic neurons as well as perisynaptic glia. Members of the neurotrophin family, which are widely expressed in the developing and mature CNS and are well-known for their roles in promoting neuronal survival and differentiation, have emerged as key synaptic modulators. However, the mechanisms by which neurotrophins modulate synapse formation and function are poorly understood. Here, we summarize our work on the role of neurotrophins in synaptogenesis in the CNS, in particular the role of these signaling molecules and their receptors, the Trks, in the development of excitatory and inhibitory hippocampal synapses. We discuss our results that demonstrate that postsynaptic TrkB signaling plays an important role in modulating the formation and maintenance of NMDA and GABAA receptor clusters at central synapses, and suggest that neurotrophin signaling coordinately modulates these receptors as part of mechanism that promotes the balance between excitation and inhibition in developing circuits. We also discuss our results that demonstrate that astrocytes promote the formation of GABAergic synapses in vitro by differentially regulating the development of inhibitory presynaptic terminals and postsynaptic GABAA receptor clusters, and suggest that glial modulation of inhibitory synaptogenesis is mediated by neurotrophin-dependent and -independent signaling. Together, these findings extend our understanding of how neuron-glia communication modulates synapse formation, maintenance and function, and set the stage for defining the cellular and molecular mechanisms by which neurotrophins and other cell-cell signals direct synaptogenesis in the developing brain.

The use of mycophenolate mofetil for the treatment of autoimmune and chronic idiopathic urticaria: Experience in 19 patients

BACKGROUND There is a paucity of investigation on which to base the treatment of chronic urticaria after a patient fails maximum therapy with antihistamines. One prospective, open-label, uncontrolled study suggested that mycophenolate mofetil may be a successful second-line therapy. OBJECTIVE We sought to evaluate the efficacy and safety of mycophenolate mofetil in 19 patients with autoimmune and chronic idiopathic urticaria. METHODS In a retrospective chart review, records of patients with autoimmune and chronic idiopathic urticaria who were evaluated between 2001 and 2009 were analyzed. RESULTS Improvement in urticaria was observed in 89% of patients, specifically 91% of patients with autoimmune urticaria and 88% with chronic idiopathic urticaria. Time to initial improvement ranged from 1 to 9 weeks. In 59% of these patients, complete control of urticaria was achieved, which included 70% of patients with autoimmune urticaria and 43% with chronic idiopathic urticaria. Mean time to complete control was 14 weeks, with a range of less than 1 to 31 weeks. The dose of mycophenolate mofetil at complete control ranged from 1000 to 6000 mg divided twice daily. Mycophenolate mofetil was tapered in 7 of these 10 patients after an average of 7 weeks. Six of the 7 patients tapered then discontinued mycophenolate mofetil with remissions lasting between 2 and 16 weeks up to when the chart review ended. Mycophenolate mofetil was well tolerated with no serious infections or laboratory abnormalities. Gastrointestinal symptoms were most common. LIMITATIONS This was a retrospective chart analysis. The number of patients was relatively small. CONCLUSIONS Mycophenolate mofetil is a useful and well-tolerated second-line therapy for patients with autoimmune and chronic idiopathic urticaria in whom antihistamines and other therapeutic agents have failed.

Redefining the concept of protease-activated receptors: cathepsin S evokes itch via activation of Mrgprs

Sensory neurons expressing Mas-related G protein coupled receptors (Mrgprs) mediate histamine-independent itch. We show that the cysteine protease cathepsin S activates MrgprC11 and evokes receptor-dependent scratching in mice. In contrast to its activation of conventional protease-activated receptors, cathepsin S mediated activation of MrgprC11 did not involve the generation of a tethered ligand. We demonstrate further that different cysteine proteases selectively activate specific mouse and human Mrgpr family members. This expansion of our understanding by which proteases interact with GPCRs redefines the concept of what constitutes a protease-activated receptor. The findings also implicate proteases as ligands to members of this orphan receptor family while providing new insights into how cysteine proteases contribute to itch.

Cathepsin S Signals via PAR2 and Generates a Novel Tethered Ligand Receptor Agonist

Protease-activated receptor-2 is widely expressed in mammalian epithelial, immune and neural tissues. Cleavage of PAR2 by serine proteases leads to self-activation of the receptor by the tethered ligand SLIGRL. The contribution of other classes of proteases to PAR activation has not been studied in detail. Cathepsin S is a widely expressed cysteine protease that is upregulated in inflammatory conditions. It has been suggested that cathepsin S activates PAR2. However, cathepsin S activation of PAR2 has not been demonstrated directly nor has the potential mechanism of activation been identified. We show that cathepsin S cleaves near the N-terminus of PAR2 to expose a novel tethered ligand, KVDGTS. The hexapeptide KVDGTS generates downstream signaling events specific to PAR2 but is weaker than SLIGRL. Mutation of the cathepsin S cleavage site prevents receptor activation by the protease while KVDGTS retains activity. In conclusion, the range of actions previously ascribed to cysteine cathepsins in general, and cathepsin S in particular, should be expanded to include molecular signaling. Such signaling may link together observations that had been attributed previously to PAR2 or cathepsin S individually. These interactions may contribute to inflammation.

Topical Therapies for Pruritus

Itch, or pruritus, is the predominant symptom associated with acute and chronic cutaneous disease, and in some cases may be debilitating. To date, there is no single universally effective anti-itch treatment. Because the pathophysiology of itch in most cutaneous or systemic disorders remains unclear, antipruritic therapy is often directed against a variety of targets, including the epidermal barrier, immune system, or the nervous system. Topical therapy is the mainstay of dermatologic management of acute or localized itch or in patients with contraindications to systemic therapies. This review will summarize current topical therapies to treat pruritus and discuss potential future therapies.

Advanced aging skin and itch: addressing an unmet need.

Itch is the most common skin disorder in the elderly and frequently diminishes quality of life in this population. The high prevalence of pruritus in elderly patients is attributed in part to the decline in the normal physiology of the advanced aging skin, and reflects poor hydration, impaired skin barrier, and altered neural function, all ultimately contributing to inflammation and pruritus. As the elderly population continues to grow, practitioners need to be aware of how to evaluate and manage pruritus, recognizing the common conditions contributing to itch in elderly patients as well as the challenges of treatment in this group. Ultimately, management of pruritus will require an individually tailored approach that is guided by a patients general health, severity of symptoms, and the potential adverse effects of itch therapies.

Multicentric glioblastoma multiforme in a patient with BRCA-1 invasive breast cancer

Abstract:  Breast cancer is the most common cancer in women. Germline mutations in BRCA‐1 and BRCA‐2 significantly increase the risk of developing breast and ovarian cancers, and are also associated with an increased incidence of primary cancers at other sites. We report the case of a 46‐year‐old woman previously treated for ductal adenocarcinoma of the breast with BRCA‐1 who subsequently was diagnosed with multicentric glioblastoma multiforme (GBM) in the right temporal and right occipital lobes. We briefly discuss the incidence of BRCA‐1 mutations in breast cancer as well as other primary neoplasms and consider potential mechanisms shared in the pathogenesis of breast and glial tumors.