Functional deficiency of MHC class i enhances LTP and abolishes LTD in the nucleus accumbens of mice

Major histocompatibility complex class I (MHCI) molecules were recently identified as novel regulators of synaptic plasticity. These molecules are expressed in various brain areas, especially in regions undergoing activity-dependent synaptic plasticity, but their role in the nucleus accumbens (NAc) is unknown. In this study, we investigated the effects of genetic disruption of MHCI function, through deletion of β2-microblobulin, which causes lack of cell surface expression of MHCI. First, we confirmed that MHCI molecules are expressed in the NAc core in wild-type mice. Second, we performed electrophysiological recordings with NAc core slices from wild-type and β2-microglobulin knock-out mice lacking cell surface expression of MHCI. We found that low frequency stimulation induced long-term depression in wild-type but not knock-out mice, whereas high frequency stimulation induced long-term potentiation in both genotypes, with a larger magnitude in knock-out mice. Furthermore, we demonstrated that knock-out mice showed more persistent behavioral sensitization to cocaine, which is a NAc-related behavior. Using this model, we analyzed the density of total AMPA receptors and their subunits GluR1 and GluR2 in the NAc core, by SDS-digested freeze-fracture replica labeling. After repeated cocaine exposure, the density of GluR1 was increased, but there was no change in total AMPA receptors and GluR2 levels in wildtype mice. In contrast, following repeated cocaine exposure, increased densities of total AMPA receptors, GluR1 and GluR2 were observed in knock-out mice. These results indicate that functional deficiency of MHCI enhances synaptic potentiation, induced by electrical and pharmacological stimulation

Parkinson’s disease-associated iPLA2-VIA/PLA2G6 regulates neuronal functions and α-synuclein stability through membrane remodeling

Mutations in the iPLA2-VIA/PLA2G6 gene are responsible for PARK14-linked Parkinson’s disease (PD) with α-synucleinopathy. However, it is unclear how iPLA2-VIA mutations lead to α-synuclein (α-Syn) aggregation and dopaminergic (DA) neurodegeneration. Here, we report that iPLA2-VIA–deficient Drosophila exhibits defects in neurotransmission during early developmental stages and progressive cell loss throughout the brain, including degeneration of the DA neurons. Lipid analysis of brain tissues reveals that the acyl-chain length of phospholipids is shortened by iPLA2-VIA loss, which causes endoplasmic reticulum (ER) stress through membrane lipid disequilibrium. The introduction of wild-type human iPLA2-VIA or the mitochondria–ER contact site-resident protein C19orf12 in iPLA2-VIA–deficient flies rescues the phenotypes associated with altered lipid composition, ER stress, and DA neurodegeneration, whereas the introduction of a disease-associated missense mutant, iPLA2-VIA A80T, fails to suppress these phenotypes. The acceleration of α-Syn aggregation by iPLA2-VIA loss is suppressed by the administration of linoleic acid, correcting the brain lipid composition. Our findings suggest that membrane remodeling by iPLA2-VIA is required for the survival of DA neurons and α-Syn stability

The Parkinson's Disease-Associated Protein Kinase LRRK2 Modulates Notch Signaling through the Endosomal Pathway

Leucine-rich repeat kinase 2 (LRRK2) is a key molecule in the pathogenesis of familial and idiopathic Parkinson’s disease (PD). We have identified two novel LRRK2-associated proteins, a HECT-type ubiquitin ligase, HERC2, and an adaptor-like protein with six repeated Neuralized domains, NEURL4. LRRK2 binds to NEURL4 and HERC2 via the LRRK2 Ras of complex proteins (ROC) domain and NEURL4, respectively. HERC2 and NEURL4 link LRRK2 to the cellular vesicle transport pathway and Notch signaling, through which the LRRK2 complex promotes the recycling of the Notch ligand Delta-like 1 (Dll1)/Delta (Dl) through the modulation of endosomal trafficking. This process negatively regulates Notch signaling through cis-inhibition by stabilizing Dll1/Dl, which accelerates neural stem cell differentiation and modulates the function and survival of differentiated dopaminergic neurons. These effects are strengthened by the R1441G ROC domain-mutant of LRRK2. These findings suggest that the alteration of Notch signaling in mature neurons is a component of PD etiology linked to LRRK2

Study on Protein Structures of Eight Mung Bean Varieties and Freeze-Thaw Stability of Protein-Stabilized Emulsions

In order to evaluate the freeze-thaw stability of mung bean protein isolate (MPI)-stabilized emulsions and its relationship with protein structure, proteins of eight mung bean varieties were compared. The results revealed that MPIs prepared from all eight varieties were mainly composed of five subunit bands, with albumin and globulin content ranges of 188.4–310.3 and 301.1–492.7 mg/g total protein, respectively. Protein structural analysis revealed that random coil structure (32.34–33.51%) accounted for greater than 30% of MPI secondary structure. Meanwhile, analysis of protein properties revealed emulsifying activity index (EAI), emulsifying stability index (ESI) and flexibility value ranges of 6.735–8.598 m2/g, 20.13–34.25% and 0.125–0.182, respectively. Measurements of freeze-thaw stability of MPI emulsions demonstrated that exposures of emulsions to multiple freeze-thaw cycles resulted in significantly different emulsion creaming index, oiling-off, particle size and zeta potential values for the various emulsions. Moreover, the stabilities of all eight protein emulsions decreased with each freeze-thaw cycle, as demonstrated using optical micrographs. The correlation analysis method was used to study the correlation between the original structures, emulsifying properties of proteins and the freeze-thaw stability of MPI emulsions. Correlation analysis results revealed significant relationships between albumin content, subunit bands with a molecular weight of 26.9 kDa and emulsifying properties were significantly related to the freeze-thaw stability of MPI emulsion. Thus, by determining these indicator values, we can predict the freeze-thaw stability of MPI-stabilized emulsions

MHCI molecules are expressed in the nucleus accumbens core in WT mice.

<p>Staining for MHCI with OX-18 antibody (upper-left), Neurogranin (upper-center) and the merged image (upper-right) are shown. Lower images represent negative controls without OX-18. Scale bar represents 50 µm.</p

Comparison of AMPA receptor densities.

<p>A) A raw electron micrograph image of SDS-FRL replica immunolabeled with pan-AMPA antibody (left), and an analyzed image (right). A representative replica from a wild type mouse treated with saline (WT-Sal) is shown. The blue area indicates intra-membrane particle clusters and the black dots indicate immunogold particles. B) Densities of pan-AMPA, GluR1, and GluR2 in WT-Sal mice and β2m mice treated with saline (β2m^−/−-Sal). The densities normalized to WT in each receptor were: pan-AMPA: β2m^−/−-Sal, 110.0±8.5%; GluR1: β2m^−/−-Sal, 92.9±7.8%; GluR2: β2m^−/−-Sal, 95.4±1.5%, n = 6 [for each receptor 6 replicas from three animals, 30 synapses per replica]. C) Comparison of pan-AMPA, GluR1 and GluR2 densities between WT-Sal mice and wild type mice treated with cocaine (WT-Coc). The densities normalized to saline group in each receptor were: pan-AMPA: WT-Coc, 119.4±8.3%; GluR1: WT–Coc, 135.3±8.9%; GluR2: WT–Coc, 105.6±9.6%, n = 6 [for each receptor six replicas from three animals, 30 synapses per replica]. D) Comparison of pan-AMPA, GluR1 and GluR2 densities between β2m^−/−-Sal mice and β2m^−/− mice treated with cocaine (β2m^−/−-Coc). The densities normalized to saline group in each receptor were: pan-AMPA: β2m^−/−-Coc, 130.9±10.0%; GluR1: β2m^−/−-Coc, 117.5±5.8%; GluR2: β2m^−/−-Coc, 119.7±6.2%, n = 6 [for each receptor six replicas from three animals, 30 synapses per replica]. E) Representative electron micrographs of the replicas from WT-Sal and WT-Coc mice. The blue area indicates intra-membrane particle clusters and the black dots indicate immunogold particles. F) Representative electron micrographs of the replicas from β2m^−/−-Sal and β2m^−/−-Coc mice. The red area indicates intra-membrane particle clusters and the black dots indicate immunogold particles. Scale bars represent 200 nm. *p<0.05.</p

Comparison of the fEPSP slopes.

<p>A) Comparison between WT mice and β2m^−/− mice after high frequency stimulation (HFS) at 100 Hz. HFS induced LTP in both groups (WT: 125.8±4.5%, n = 9/N = 5, T = 1, p<0.01; β2m^−/−: 141.8±5.7%, n = 11/N = 6, T = 0, p<0.001; Signed rank test), whereas LTP was enhanced in the β2m^−/− group (t(18) = 2.107, p<0.05; Student’s t-test). B) Comparison between WT and β2m^−/− mice after low frequency stimulation (LFS) at 10 Hz. LFS induced LTD in WT mice (79.2±5.9%, n = 9/N = 6, T = 1, p<0.05), whereas it was ineffective in β2m^−/− mice (103.2±7.3%, n = 9/N = 6, T = 18, p = 0.65). At 45–50 min after LFS, the fEPSP slope in β2m^−/− mice was significantly higher than in WT mice (t(16) = 2.548, p<0.05). C) Comparison between WT and β2m^−/− mice after 1 Hz stimulation. Neither LTP nor LTD was induced by this stimulation (WT: 103.4±7.1%, n = 7/N = 6, T = 9, p = 0.47; β2m^−/−: 100.7±5.7%, n = 7/N = 6, T = 12, p = 0.81). There was no significant difference in the fEPSP slope at 45–50 min after 1 Hz/15 min stimulation between genotypes (t(12) = 0.302, p = 0.768). D) Comparison of paired pulse ratios (PPRs). (Left) PPRs in WT and β2m^−/− mice at 30, 50 and 100 ms inter stimulus interval (ISI). There was no significant difference in the PPRs of WT (ISI 30 ms: 117.9±2.4%; ISI 50 ms: 124.5±2.6%; ISI100 ms: 111.7±1.0%) (n = 9/N = 5) and β2m^−/− (ISI 30 ms: 116.8±1.9%; ISI 50 ms: 123.2±2.3%; ISI 100 ms: 111.5±0.8%) (n = 9/N = 5) mice, in all tested ISIs (ISI 30 ms: t(16) = 0.349, p = 0.731; ISI 50 ms: t(16) = 0.355, p = 0.727; ISI 100 ms: t(16) = 0.164, p = 0.872). (Right) Representative traces of fEPSPs at 50 ms inter stimulus interval (blue: WT; red: β2m^−/−). Vertical scale bars represent 100 µV, and horizontal scale bars represent 10 ms. *p<0.05. n = slices/N = animals.</p