Vacuolar protein sorting-35 (VPS35) is essential for endosome-to-Golgi retrieval of membrane proteins. Mutations in the VPS35 gene have been identified in patients with autosomal dominant PD. However, it remains poorly understood if and how VPS35 deficiency or mutation contributes to PD pathogenesis. Here we provide evidence that links VPS35 deficiency to PD-like neuropathology. VPS35 was expressed in mouse dopamine (DA) neurons in substantia nigra pars compacta (SNpc) and STR (striatum)-regions that are PD vulnerable. VPS35-deficient mice exhibited PD-relevant deficits including accumulation of ␣-synuclein in SNpc-DA neurons, loss of DA transmitter and DA neurons in SNpc and STR, and impairment of locomotor behavior. Further mechanical studies showed that VPS35-deficient DA neurons or DA neurons expressing PD-linked VPS35 mutant (D620N) had impaired endosome-to-Golgi retrieval of lysosome-associated membrane glycoprotein 2a (Lamp2a) and accelerated Lamp2a degradation. Expression of Lamp2a in VPS35-deficient DA neurons reduced ␣-synuclein, supporting the view for Lamp2a as a receptor of chaperone-mediated autophagy to be critical for ␣-synuclein degradation. These results suggest that VPS35 deficiency or mutation promotes PD pathogenesis and reveals a crucial pathway, VPS35-Lamp2a-␣-synuclein, to prevent PD pathogenesis.

Neuregulin 1 (NRG1) is a trophic factor thought to play a role in neural development. Recent studies suggest that it may regulate neurotransmission, mechanisms of which remain elusive. Here we show that NRG1, via stimulating GABA release from interneurons, inhibits pyramidal neurons in the prefrontal cortex (PFC). Ablation of the NRG1 receptor ErbB4 in parvalbumin (PV)-positive interneurons prevented NRG1 from stimulating GABA release and from inhibiting pyramidal neurons. PV-ErbB4 −/− mice exhibited schizophrenia-relevant phenotypes similar to those observed in NRG1 or ErbB4 null mutant mice, including hyperactivity, impaired working memory, and deficit in prepulse inhibition (PPI) that was ameliorated by diazepam, a GABA enhancer. These results indicate that NRG1 regulates the activity of pyramidal neurons by promoting GABA release from PV-positive interneurons, identifying a critical function of NRG1 in balancing brain activity. Because both NRG1 and ErbB4 are susceptibility genes of schizophrenia, our study provides insight into potential pathogenic mechanisms of schizophrenia and suggests that PV-ErbB4 −/− mice may serve as a model in the study of this and relevant brain disorders.is a family of trophic factors with an epidermal growth factor (EGF)-like domain (1, 2). It acts by stimulating the ErbB family of receptor tyrosine kinases ErbB2, -3, and -4. NRG1 binds only to ErbB3 or ErbB4, but not to ErbB2. On the other hand, ErbB2 and ErbB4 are most active in response to NRG1 stimulation whereas the kinase activity of ErbB3 is impaired. Thus, ErbB2 and ErbB3 function by forming heterodimers with each other or with ErbB4, but an ErbB4 homodimer is functional by itself (2). NRG1 has been implicated in many aspects of neural development including neuron migration, axon projection, myelination, synapse formation, and up-regulation of neurotransmitter receptor expression (2). Recently, CNS-specific mutation of ErbB2 and ErbB4 seemed to have no effect on layered structures of the cerebral cortex, hippocampus, and cerebellum or expression of NMDA receptor subtypes (3, 4), challenging existing views of NRG1 function.Both NRG1 and its receptors are distributed throughout brain regions critical for higher function in adult animals (5-8), suggesting a role of NRG1 in the brain after neural development is complete. In support of this hypothesis were observations that ErbB4 is present at the postsynaptic density of excitatory synapses presumably via interaction with PSD-95 (9-11). Moreover, ErbB4 mRNA is enriched in regions where interneurons are clustered (5) and GAD-positive neurons of the hippocampus express high levels of ErbB4 (10), suggesting that ErbB4 is enriched in GABAergic neurons. Immunohistochemical analysis indicates that ErbB4 is expressed in most if not all parvalbumin (PV)-positive interneurons in addition to glutamatergic neurons (10, 12). Intriguingly, exogenous NRG1 suppresses the induction of LTP at Schaffer collateral-CA1 synapses in the hippocampus (10, 11, 13) or reverses it (14, 15). These observ...

Neuregulin 1 (NRG1) is a trophic factor that acts by stimulating ErbB receptor tyrosine kinases and has been implicated in neural development and synaptic plasticity. In this study, we investigated mechanisms of its suppression of long-term potentiation (LTP) in the hippocampus. We found that NRG1 did not alter glutamatergic transmission at SC-CA1 synapses but increased the GABA A receptormediated synaptic currents in CA1 pyramidal cells via a presynaptic mechanism. Inhibition of GABA A receptors blocked the suppressing effect of NRG1 on LTP and prevented ecto-ErbB4 from enhancing LTP, implicating a role of GABAergic transmission. To test this hypothesis further, we generated parvalbumin (PV)-Cre;ErbB4 −/− mice in which ErbB4, an NRG1 receptor in the brain, is ablated specifically in PV-positive interneurons. NRG1 was no longer able to increase inhibitory postsynaptic currents and to suppress LTP in PV-Cre; ErbB4 −/− hippocampus. Accordingly, contextual fear conditioning, a hippocampus-dependent test, was impaired in PV-Cre;ErbB4 −/− mice. In contrast, ablation of ErbB4 in pyramidal neurons had no effect on NRG1 regulation of hippocampal LTP or contextual fear conditioning. These results demonstrate a critical role of ErbB4 in PV-positive interneurons but not in pyramidal neurons in synaptic plasticity and support a working model that NRG1 suppresses LTP by enhancing GABA release. Considering that NRG1 and ErbB4 are susceptibility genes of schizophrenia, these observations contribute to a better understanding of how abnormal NRG1/ErbB4 signaling may be involved in the pathogenesis of schizophrenia. N euregulin 1 (NRG1) is a trophic factor that acts by activating ErbB receptor tyrosine kinases, including ErbB4. NRG1 signaling has been implicated in various steps in neural development, including neuron migration, axon guidance, synapse formation, and expression of neurotransmitter receptors (1). Studies of NRG1 have attracted much attention because both NRG1 and ErbB4 were identified as susceptibility genes of schizophrenia and NRG1 and ErbB4 mutant mice show schizophrenia-relevant behaviors (1-4).Recent studies suggest that NRG1 plays a role in neurotransmission and synaptic plasticity (1). NRG1 has been shown to suppress the induction of LTP acutely at Schaffer collateral (SC)-CA1 synapses in adult rodent hippocampus (5-8), but it has no effect on basal synaptic transmission (5, 7, 9). NRG1 regulation of long-term potentiation (LTP) requires ErbB4 (8); however, underlying mechanisms remain unclear. In vitro studies suggest that NRG1 may alter functions of pyramidal neurons and glutamatergic transmission. For example, it could suppress NMDA receptor (NMDAR) currents in prefrontal cortical (PFC) neurons in culture (10). NRG1 was shown to stimulate internalization of surface AMPA receptors (AMPARs) in dissociated hippocampal neurons (11). Moreover, changes in ErbB4 levels in neonatal hippocampal slices alter dendritic spine size and AMPA synaptic currents (12). Conversely, ErbB4 expression is largely restricted to ...

Myasthenia gravis (MG) is the most common disorder affecting the neuromuscular junction (NMJ). MG is frequently caused by autoantibodies against acetylcholine receptor (AChR) and a kinase critical for NMJ formation, MuSK; however, a proportion of MG patients are double-negative for anti-AChR and anti-MuSK antibodies. Recent studies in these subjects have identified autoantibodies against low-density lipoprotein receptor-related protein 4 (LRP4), an agrin receptor also critical for NMJ formation. LRP4 autoantibodies have not previously been implicated in MG pathogenesis. Here we demonstrate that mice immunized with the extracellular domain of LRP4 generated anti-LRP4 antibodies and exhibited MG-associated symptoms, including muscle weakness, reduced compound muscle action potentials (CMAPs), and compromised neuromuscular transmission. Additionally, fragmented and distorted NMJs were evident at both the light microscopic and electron microscopic levels. We found that anti-LRP4 sera decreased cell surface LRP4 levels, inhibited agrin-induced MuSK activation and AChR clustering, and activated complements, revealing potential pathophysiological mechanisms. To further confirm the pathogenicity of LRP4 antibodies, we transferred IgGs purified from LRP4-immunized rabbits into naive mice and found that they exhibited MG-like symptoms, including reduced CMAP and impaired neuromuscular transmission. Together, these data demonstrate that LRP4 autoantibodies induce MG and that LRP4 contributes to NMJ maintenance in adulthood.