Major depression is a highly prevalent severe mood disorder that is treated with antidepressants. The molecular targets of antidepressants require definition. We investigated the role of the acid sphingomyelinase (Asm)-ceramide system as a target for antidepressants. Therapeutic concentrations of the antidepressants amitriptyline and fluoxetine reduced Asm activity and ceramide concentrations in the hippocampus, increased neuronal proliferation, maturation and survival and improved behavior in mouse models of stress-induced depression. Genetic Asm deficiency abrogated these effects. Mice overexpressing Asm, heterozygous for acid ceramidase, treated with blockers of ceramide metabolism or directly injected with C16 ceramide in the hippocampus had higher ceramide concentrations and lower rates of neuronal proliferation, maturation and survival compared with controls and showed depression-like behavior even in the absence of stress. The decrease of ceramide abundance achieved by antidepressant-mediated inhibition of Asm normalized these effects. Lowering ceramide abundance may thus be a central goal for the future development of antidepressants. DOI: https://doi.org/10. 1038/nm.3214 Posted at the Zurich Open Repository and Archive, University of Zurich ZORA URL: https://doi.org/10.5167/uzh-79905 Accepted Version Originally published at: Gulbins, E; Palmada, M; Reichel, M; Lüth, A; Böhmer, C; Amato, D; Müller, C P; Tischbirek, C H; Groemer, T W; Tabatabai, G; Becker, K A; Tripal, P; Staedtler, S; Ackermann, T F; van Brederode, J; Alzheimer, C; Weller, M; Lang, U E; Kleuser, B; Grassme, H; Kornhuber, J (2013). Acid sphingomyelinaseceramide system mediates effects of antidepressant drugs. Nature Medicine, 19 (7) Major depression may be triggered by psychological stress, inflammatory cytokines, and dysfunction of the hypothalamic-pituitary-adrenal axis, etc. 1-4 .The previously held monoamine hypothesis for the action of antidepressants has been questioned because the antidepressant effect of these drugs is not clearly associated with their monoaminergic effect; in fact, the antidepressant tianeptine is even a serotonin reuptake enhancer 5 . Furthermore, the direct effect on monoamines contrasts with the delay of antidepressant effects in patients. Recent concepts of the pathogenesis of major depression suggest a change of cellular plasticity predominantly in the hippocampus and a shift in the balance between neurogenic and antiapoptotic events that leads to neurodegeneration and hippocampal atrophy [6][7][8][9] . Antidepressants increase neurogenesis and reverse hippocampal atrophy associated with major depression 9 .Here, we tested the role of the acid sphingomyelinase (EC 3.1.4.12, sphingomyelin phosphodiesterase, human protein: ASM, murine protein: Asm, gene symbol: Smpd1) and ceramide system as a target for antidepressants. Asm is ubiquitously expressed and releases ceramide from sphingomyelin, predominantly in lysosomes but also in secretory lysosomes and on the plasma membrane 10-13 .The antidepres...

␤-Secretase (BACE1) is the rate-limiting protease for the generation of the amyloid ␤-peptide (A␤) in Alzheimer disease. Mice in which the bace1 gene is inactivated are reported to be healthy. However, the presence of a homologous gene encoding BACE2 raises the possibility of compensatory mechanisms. Therefore, we have generated bace1, bace2, and double knockout mice. We report here that BACE1 mice display a complex phenotype. A variable but significant number of BACE1 offspring died in the first weeks after birth. The surviving mice remained smaller than their littermate controls and presented a hyperactive behavior. Electrophysiologically, subtle alterations in the steady-state inactivation of voltage-gated sodium channels in BACE1-deficient neurons were observed. In contrast, bace2 knockout mice displayed an overall healthy phenotype. However, a combined deficiency of BACE2 and BACE1 enhanced the bace1 ؊/؊ lethality phenotype. At the biochemical level, we have confirmed that BACE1 deficiency results in an almost complete block of A␤ generation in neurons, but not in glia. As glia are 10 times more abundant in brain compared with neurons, our data indicate that BACE2 could indeed contribute to A␤ generation in the brains of Alzheimer disease and, in particular, Down syndrome patients. In conclusion, our data challenge the general idea of BACE1 as a safe drug target and call for some caution when claiming that no major side effects should be expected from blocking BACE1 activity. Alzheimer disease (AD)1 is the most common cause of dementia for which neither a good diagnostic test nor an effective treatment is available yet. The most widely accepted hypothesis states that AD is initially triggered by the abnormal accumulation and possibly deposition of the small amyloid ␤-peptide (A␤) in different brain regions, which in turn initiates a pathogenic cascade that ultimately leads to neuronal death, AD pathology, and dementia. A␤ is cleaved from a long membranebound precursor, the amyloid precursor protein (APP), by two consecutive cleavages. ␤-and ␥-secretases are the enzymes that liberate the N and C termini of A␤, respectively, and are the subject of intense investigation because of their relevance as candidate therapeutic targets to treat AD.BACE1 and BACE2 are two highly homologous membranebound aspartyl proteases that can process APP at the ␤-secretase site (1-8). Although both enzymes exhibit many of the characteristics expected for ␤-secretase, it has been quite convincingly demonstrated that BACE1 is in fact the major ␤-secretase responsible for A␤ generation in brain (9 -11). Contrary to BACE1, BACE2 is more highly expressed in peripheral tissues, but also to some extent in brain (2,8,12,13), raising the question of whether BACE2 could contribute to the generation of the brain A␤ pool. Both BACE1 and BACE2 can cleave APP in vitro not only at Asp 1 (numbering considering the first amino acid of A␤ as position 1), but also at internal sites within the A␤ region. BACE1 cleaves between amino acids 10 and 11 o...

This report describes the behavioral and electrophysiological analysis of regulatable transgenic mice expressing mutant repeat domains of human Tau (Tau RD ). Mice were generated to express Tau RD in two forms, differing in their propensity for ␤-structure and thus in their tendency for aggregation ("pro-aggregant" or "anti-aggregant") (Mocanu et al., 2008). Only pro-aggregant mice show pronounced changes typical for Tau pathology in Alzheimer's disease (aggregation, missorting, hyperphosphorylation, synaptic and neuronal loss), indicating that the ␤-propensity and hence the ability to aggregate is a key factor in the disease. We now tested the mice with regard to neuromotor parameters, behavior, learning and memory, and synaptic plasticity and correlated this with histological and biochemical parameters in different stages of switching Tau RD on or off. The mice are normal in neuromotor tests. However, pro-aggregant Tau RD mice are strongly impaired in memory and show pronounced loss of long-term potentiation (LTP), suggesting that Tau aggregation specificallyperturbsthesebrainfunctions.Remarkably,whentheexpressionofhumanpro-aggregantTau RD isswitchedonforϳ10monthsand off for ϳ4 months, memory and LTP recover, whereas aggregates decrease moderately and change their composition from mixed human plus mouse Tau to mouse Tau only. Neuronal loss persists, but synapses are partially rescued. This argues that continuous presence of amyloidogenic pro-aggregant Tau RD constitutes the main toxic insult for memory and LTP, rather than the aggregates as such.

The kinetic behavior of brain Na+ channels was studied in pyramidal cells from rat and cat sensorimotor cortex using either the thin slice preparation or acutely isolated neurons. Single-channel recordings were obtained in the cell-attached and inside-out configuration of the patch-clamp technique. Na+ channels had a conductance of about 16 pS. Patches always contained several Na+ channels, usually 4-12. In both preparations, long depolarizing pulses revealed two distinct patterns of late Na+ channel activity following transient openings. (1) Na+ channels displayed sporadic brief late openings sometimes clustered to "minibursts" of 10-40 msec. These events occurred at a low frequency, yielding open probability (NPo) values below 0.01 (mean = 0.0034). (2) In the second gating mode, an individual Na+ channel in the patch failed to inactivate and produced a burst of openings often lasting to the end of the pulse. This behavior was observed in about 1% of depolarizations. Shifts to the bursting mode were usually confined to a single 400 msec pulse, but rarely occurred during two or more consecutive pulses applied at 2 sec intervals. Sustained bursts did not require preceding transient openings to occur since they were also observed during slow depolarizing voltage ramps. The similar incidence of inactivation failures in cell-attached versus inside-out recordings suggests that the bursting mode is a property of the channel and/or adjacent membrane-bound structures. Calculations indicate that brief late openings and rare sustained bursts suffice to generate a small but significant whole-cell current. Since the Na+ channels mediating early, brief late, and sustained openings were identical in terms of their elementary electrical properties, we propose that the fast and the persistent Na+ currents of cortical pyramidal cells are generated by an electrophysiologically uniform population of Na+ channels that can individually switch between different gating modes.

Infusion of the chemotherapeutic agent oxaliplatin leads to an acute and a chronic form of peripheral neuropathy. Acute oxaliplatin neuropathy is characterized by sensory paresthesias and muscle cramps that are notably exacerbated by cooling. Painful dysesthesias are rarely reported for acute oxaliplatin neuropathy, whereas a common symptom of chronic oxaliplatin neuropathy is pain. Here we examine the role of the sodium channel isoform Na V 1.6 in mediating the symptoms of acute oxaliplatin neuropathy. Compound and single-action potential recordings from human and mouse peripheral axons showed that cooling in the presence of oxaliplatin (30-100 μM; 90 min) induced bursts of action potentials in myelinated A, but not unmyelinated C-fibers. Whole-cell patch-clamp recordings from dissociated dorsal root ganglion (DRG) neurons revealed enhanced tetrodotoxin-sensitive resurgent and persistent current amplitudes in large, but not small, diameter DRG neurons when cooled (22°C) in the presence of oxaliplatin. In DRG neurons and peripheral myelinated axons from Scn8a med/med mice, which lack functional Na V 1.6, no effect of oxaliplatin and cooling was observed. Oxaliplatin significantly slows the rate of fast inactivation at negative potentials in heterologously expressed mNa V 1.6r in ND7 cells, an effect consistent with prolonged Na V open times and increased resurgent and persistent current in native DRG neurons. This finding suggests that Na V 1.6 plays a central role in mediating acute cooling-exacerbated symptoms following oxaliplatin, and that enhanced resurgent and persistent sodium currents may provide a general mechanistic basis for cold-aggravated symptoms of neuropathy.chemotherapy | peripheral nerve | abnormal axonal excitability | repetitive action potential discharge C linical use of the highly effective chemotherapeutic oxaliplatin is compromised by an acute and a chronic form of peripheral neuropathy. Acutely, 85-90% of patients exhibit muscle fasciculations (1, 2), sensory paresthesias, and occasional dysesthesias (3), all triggered by mild cooling. Although chronic oxaliplatin-induced neuropathy has been recently linked to changes in the expression and sensitivity of transient receptor potential (TRP) channels TRPM8 and TRPA1 (4, 5), two-pore domain potassium channels (TREK1, TRAAK) and the hyperpolarization-activated channel HCN1 (6), the mechanism underlying acute oxaliplatin neuropathy remains unresolved. Several candidate mechanisms have been proposed including potassium channel blockade (7), calcium chelation (8), and alterations in voltage-gated sodium channel (Na V ) kinetics (9, 10), but none adequately account for motor and sensory symptoms nor their exacerbation by cooling.