Background Hemodynamic load regulates myocardial function and gene expression. We tested the hypothesis that afterload and preload despite similar average load result in different phenotypes. Methods and Results Afterload and preload were compared in mice with transversal aortic constriction (TAC) and aorto-caval shunt (Shunt). When compared to sham mice, six hours after surgery, systolic wall stress (afterload) was increased in TAC (+40%, P<0.05), diastolic wall stress (preload) was increased in Shunt (+277%, P<0.05) and TAC (+74%, P<0.05) and mean total wall stress was similarly increased in TAC (69%) and Shunt (67%) (TAC vs. Shunt: not significant (n.s.), each P<0.05 vs. Sham). At 1 week, left ventricular weight/tibia length was significantly increased by 22% in TAC and 29% in Shunt (n.s. TAC vs. Shunt). After 24 hours and 1 week, calcium/calmodulin dependent protein kinase II (CaMKII) signaling was increased in TAC. This resulted in altered calcium cycling, including increased L-type calcium current, calcium transients, fractional SR release and calcium spark frequency. In Shunt, Akt phosphorylation was increased. TAC was associated with inflammation, fibrosis and cardiomyocyte apoptosis. The latter was significantly reduced in CaMKIIδ-KO TAC mice. 157 mRNAs and 13 microRNAs were differentially regulated in TAC vs. Shunt. After 8 weeks, fractional shortening was lower and mortality higher in TAC Conclusions Afterload results in maladaptive fibrotic hypertrophy with CaMKII-dependent altered calcium cycling and apoptosis. Preload is associated with Akt activation without fibrosis, little apoptosis, better function and lower mortality. This indicates that different loads result in distinct phenotype differences which may require specific pharmacological interventions.

Neuroligins (NL1-NL4) are postsynaptic adhesion proteins that control the maturation and function of synapses in the central nervous system (CNS). Loss-of-function mutations in NL4 are linked to rare forms of monogenic heritable autism, but its localization and function are unknown. Using the retina as a model system, we show that NL4 is preferentially localized to glycinergic postsynapses and that the loss of NL4 is accompanied by a reduced number of glycine receptors mediating fast glycinergic transmission. Accordingly, NL4-deficient ganglion cells exhibit slower glycinergic miniature postsynaptic currents and subtle alterations in their stimuluscoding efficacy, and inhibition within the NL4-deficient retinal network is altered as assessed by electroretinogram recordings. These data indicate that NL4 shapes network activity and information processing in the retina by modulating glycinergic inhibition. Importantly, NL4 is also targeted to inhibitory synapses in other areas of the CNS, such as the thalamus, colliculi, brainstem, and spinal cord, and forms complexes with the inhibitory postsynapse proteins gephyrin and collybistin in vivo, indicating that NL4 is an important component of glycinergic postsynapses.synaptogenesis | inhibitory transmission | visual processing I n rodents, postsynaptic adhesion proteins of the neuroligin family (NL1-NL4) are expressed throughout the central nervous system (CNS) (1-3) and essential for synapse organization and function (2-5). In vivo, each NL isoform localizes to specific synapse subpopulations, with NL1, NL2, and NL3 predominantly associating with glutamatergic, GABAergic, or both types of postsynapses, respectively (1, 6-9).Thus far, the distribution and function of the fourth NL isoform has remained unclear, despite the wide interest triggered by the causal link of specific loss-of-function mutations in NL4 to cases of autism, which led to the notion that aberrant synaptic transmission may cause autism spectrum disorders (ASDs) (10).We examined the distribution of NL4 in the mouse retina, a well-characterized region of the CNS with distinct, topographically organized glutamatergic, GABAergic, and glycinergic synapses, which has recently allowed us to characterize crucial aspects of NL2 distribution and function (8). Additionally, we assessed NL4 function by studying synaptic activity and visual processing in the NL4-deficient (NL4-KO; ref.3) mouse retina. Finally, we studied NL4 localization in the rest of the CNS and identified some of its key binding partners at the synapse. Results NL4 Is Localized to Glycinergic Postsynapses in the Retina.We characterized the distribution of NL4 by immunohistochemistry by using an isoform-specific antibody (3) (Fig. 1). A punctate labeling was detected in the inner plexiform layer (IPL) of wildtype (WT) but not NL4-KO retinae (Fig. 1A). NL4-positive puncta were abundant in the outer IPL but sparse in the rest of the IPL (Fig. 1A), which is reminiscent of glycine receptor (GlyR) distribution in the retina (11,12). Indeed, upon co...

We tested the influence of a photothrombotic lesion in somatosensory cortex on plasticity in the mouse visual system and the efficacy of anti-inflammatory treatment to rescue compromised learning. To challenge plasticity mechanisms, we induced monocular deprivation (MD) in 3-mo-old mice. In control animals, MD induced an increase of visual acuity of the open eye and an ocular dominance (OD) shift towards this eye. In contrast, after photothrombosis, there was neither an enhancement of visual acuity nor an OD-shift. However, OD-plasticity was present in the hemisphere contralateral to the lesion. Anti-inflammatory treatment restored sensory learning but not OD-plasticity, as did a 2-wk delay between photothrombosis and MD. We conclude that (i) both sensory learning and cortical plasticity are compromised in the surround of a cortical lesion; (ii) transient inflammation is responsible for impaired sensory learning, suggesting anti-inflammatory treatment as a useful adjuvant therapy to support rehabilitation following stroke; and (iii) OD-plasticity cannot be conceptualized solely as a local process because nonlocal influences are more important than previously assumed.

Duplication of PLP1 (proteolipid protein gene 1) and the subsequent overexpression of the myelin protein PLP (also known as DM20) in oligodendrocytes is the most frequent cause of Pelizaeus-Merzbacher disease (PMD), a fatal leukodystrophy without therapeutic options. PLP binds cholesterol and is contained within membrane lipid raft microdomains. Cholesterol availability is the rate-limiting factor of central nervous system myelin synthesis. Transgenic mice with extra copies of the Plp1 gene are accurate models of PMD. Dysmyelination followed by demyelination, secondary inflammation and axon damage contribute to the severe motor impairment in these mice. The finding that in Plp1-transgenic oligodendrocytes, PLP and cholesterol accumulate in late endosomes and lysosomes (endo/lysosomes), prompted us to further investigate the role of cholesterol in PMD. Here we show that cholesterol itself promotes normal PLP trafficking and that dietary cholesterol influences PMD pathology. In a preclinical trial, PMD mice were fed a cholesterol-enriched diet. This restored oligodendrocyte numbers and ameliorated intracellular PLP accumulation. Moreover, myelin content increased, inflammation and gliosis were reduced and motor defects improved. Even after onset of clinical symptoms, cholesterol treatment prevented disease progression. Dietary cholesterol did not reduce Plp1 overexpression but facilitated incorporation of PLP into myelin membranes. These findings may have implications for therapeutic interventions in patients with PMD.

In the brain, including the retina, interneurons show an enormous structural and functional diversity. Retinal horizontal cells represent a class of interneurons that form triad synapses with photoreceptors and ON bipolar cells. At this first retinal synapse, horizontal cells modulate signal transmission from photoreceptors to bipolar cells by feedback and feedforward inhibition. To test how the fully developed retina reacts to the specific loss of horizontal cells, these interneurons were specifically ablated from adult mice using the diphtheria toxin (DT)/DT-receptor system and the connexin57 promoter. Following ablation, the retinal network responded with extensive remodeling: rods retracted their axons from the outer plexiform layer and partially degenerated, whereas cones survived. Cone pedicles remained in the outer plexiform layer and preserved synaptic contacts with OFF but not with ON bipolar cells. Consistently, the retinal ON pathway was impaired, leading to reduced amplitudes and prolonged latencies in electroretinograms. However, ganglion cell responses showed only slight changes in time course, presumably because ON bipolar cells formed multiple ectopic synapses with photoreceptors, and visual performance, assessed with an optomotor system, was only mildly affected. Thus, the loss of an entire interneuron class can be largely compensated even by the adult retinal network.