Glial reaction is a common feature of neurodegenerative diseases. Recent studies have suggested that reactive astrocytes gain neurotoxic properties, but exactly how reactive astrocytes contribute to neurotoxicity remains to be determined. Here, we identify lipocalin 2 (lcn2) as an inducible factor that is secreted by reactive astrocytes and that is selectively toxic to neurons. We show that lcn2 is induced in reactive astrocytes in transgenic rats with neuronal expression of mutant human TAR DNA-binding protein 43 (TDP-43) or RNA-binding protein fused in sarcoma (FUS). Therefore, lcn2 is induced in activated astrocytes in response to neurodegeneration, but its induction is independent of TDP-43 or FUS expression in astrocytes. We found that synthetic lcn2 is cytotoxic to primary neurons in a dose-dependent manner, but is innocuous to astrocytes, microglia, and oligodendrocytes. Lcn2 toxicity is increased in neurons that express a disease gene, such as mutant FUS or TDP-43. Conditioned medium from rat brain slice cultures with neuronal expression of mutant TDP-43 contains abundant lcn2 and is toxic to primary neurons as well as neurons in cultured brain slice from WT rats. Partial depletion of lcn2 by immunoprecipitation reduced conditioned medium-mediated neurotoxicity. Our data indicate that reactive astrocytes secrete lcn2, which is a potent neurotoxic mediator.amyotrophic lateral sclerosis | astrocytosis G lial reaction is a common feature of neurodegenerative diseases, including amyotrophic lateral sclerosis (ALS), frontotemporal lobar degeneration (FTLD), Huntington disease, Parkinson disease, and Alzheimer's disease. Astrocytes and microglia become reactive during neurodegenerative processes (1, 2), and activated astrocytes may exhibit differential expression of astrocytic receptors, transporters, and transmitters; metabolic changes; and altered synthesis and release of proteins, chemokines, and cytokines (3-6). Controlled activation of astrocytes is considered beneficial to neurons (7), but overactive astrocytes can be harmful (8). Astrocytosis in neurodegeneration has been intensively studied, but exactly how reactive astrocytes contribute to neurotoxicity remains to be determined.Reactive astrocytes may lose neuroprotective functions or gain neurotoxic properties in neurodegenerative diseases. Astrocytes are responsible for the reuptake of the neurotransmitter glutamate, which is accomplished by excitatory amino acid transporter 2 (EAAT2 or GLT1) (9). In mice, GLT1 deficiency leads to synaptic glutamate accumulation and subsequent excitotoxicity (9). Astrocytes become reactive during neurodegeneration and gradually lose GLT1 function and expression (10-12). Stimulating GLT1 expression with antibiotics protects motor neurons in an ALS model (13). Because reactive astrocytes may lose their neuroprotective abilities, as observed during GLT1 deficiency (10-12), supplementing normal astrocytes to the areas of active neuropathology is expected to have a therapeutic effect. Indeed, transgenic rats with ALS are...

Mutation of Tar DNA-binding protein 43 (TDP-43) is linked to amyotrophic lateral sclerosis. Although astrocytes have important roles in neuron function and survival, their potential contribution to TDP-43 pathogenesis is unclear. Here, we created novel lines of transgenic rats that express a mutant form of human TDP-43 (M337V substitution) restricted to astrocytes. Selective expression of mutant TDP-43 in astrocytes caused a progressive loss of motor neurons and the denervation atrophy of skeletal muscles, resulting in progressive paralysis. The spinal cord of transgenic rats also exhibited a progressive depletion of the astroglial glutamate transporters GLT-1 and GLAST. Astrocytic expression of mutant TDP-43 led to activation of astrocytes and microglia, with an induction of the neurotoxic factor Lcn2 in reactive astrocytes that was independent of TDP-43 expression. These results indicate that mutant TDP-43 in astrocytes is sufficient to cause noncell-autonomous death of motor neurons. This motor neuron death likely involves deficiency in neuroprotective genes and induction of neurotoxic genes in astrocytes.

Patients with liver diseases often suffer from chronic itch, yet the pruritogen(s) and receptor(s) remain largely elusive. Here, we identify bile acids as natural ligands for MRGPRX4. MRGPRX4 is expressed in human dorsal root ganglion (hDRG) neurons and co-expresses with itch receptor HRH1. Bile acids elicited Ca2+ responses in cultured hDRG neurons, and bile acids or a MRGPRX4 specific agonist induced itch in human subjects. However, a specific agonist for another bile acid receptor TGR5 failed to induce itch in human subjects and we find that human TGR5 is not expressed in hDRG neurons. Finally, we show positive correlation between cholestatic itch and plasma bile acids level in itchy patients and the elevated bile acids is sufficient to activate MRGPRX4. Taken together, our data strongly suggest that MRGPRX4 is a novel bile acid receptor that likely underlies cholestatic itch in human, providing a promising new drug target for anti-itch therapies.

Mutations in ubiquilin 2 (Ubqln2) is linked to amyotrophic lateral sclerosis and frontotemporal lobar degeneration. A foremost question regarding Ubqln2 pathogenesis is whether pathogenically mutated Ubqln2 causes neuron death via a gain or loss of functions. To better understand Ubqln2 pathobiology, we created Ubqln2 transgenic and knockout rats and compared phenotypic expression in these novel rat models. Overexpression of Ubqln2 with a pathogenic mutation (P497H substitution) caused cognitive deficits and neuronal loss in transgenic rats at the age of 130 days. In the transgenic rats, neuronal loss was preceded by the progressive formation of Ubqln2 aggregates and was accompanied by the progressive accumulation of the autophagy substrates p62 and LC3-II and the impairment of endosome pathways. In contrast, none of these pathologies observed in mutant Ubqln2 transgenic rats was detected in Ubqln2 knockout rats at the age of 300 days. Together, our findings in Ubqln2 transgenic and knockout rats collectively suggest that pathogenic Ubqln2 causes neuron death mainly through a gain of unrevealed functions rather than a loss of physiological functions.

In this study we examined fasted and refed cfos activation in cortical, brainstem, and hypothalamic brain regions associated with appetite regulation. We examined a number of time points during refeeding to gain insight into the temporal pattern of neuronal activation and changes in endocrine parameters associated with fasting and refeeding. In response to refeeding, blood glucose and plasma insulin returned to basal levels within 30 minutes, whereas plasma nonesterified fatty acids and leptin returned to basal levels after 1 and 2 hours, respectively. Within the hypothalamic arcuate nucleus (ARC), fasting increased cfos activation in ∼25% of neuropeptide Y neurons, which was terminated 1 hour after refeeding. Fasting had no effect on cfos activation in pro-opiomelanocortin neurons; however, 1 and 2 hours of refeeding significantly activated ∼20% of ARC pro-opiomelanocortin neurons. Acute refeeding (30, 60, and 120 minutes), but not fasting, increased cfos activation in the nucleus accumbens, the cingulate cortex (but not the insular cortex), the medial and lateral parabrachial nucleus, the nucleus of the solitary tract, the area postrema, the dorsal raphe, and the ventromedial nucleus of the hypothalamus. After 6 hours of refeeding, cfos activity was reduced in the majority of these regions compared with that at earlier time points. Our data indicate that acute refeeding, rather than long-term fasting, activates cortical, brainstem, and hypothalamic neural circuits associated with appetite regulation and reward processing. Although the hypothalamic ARC remains a critical sensory node detecting changes in the metabolic state and feedback during fasting and acute refeeding, our results also reveal the temporal pattern in cfos activation in cortical and brainstem areas implicated in the control of appetite and body weight regulation.