Phenotypic profiling of mGlu7 knockout mice reveals new implications for neurodevelopmental disorders

Neurodevelopmental disorders are characterized by deficits in communication, cognition, attention, social behavior and/or motor control. Previous studies have pointed to the involvement of genes that regulate synaptic structure and function in the pathogenesis of these disorders. One such gene, GRM7, encodes the metabotropic glutamate receptor 7 (mGlu₇), a G protein‐coupled receptor that regulates presynaptic neurotransmitter release. Mutations and polymorphisms in GRM7 have been associated with neurodevelopmental disorders in clinical populations; however, limited preclinical studies have evaluated mGlu₇ in the context of this specific disease class. Here, we show that the absence of mGlu₇ in mice is sufficient to alter phenotypes within the domains of social behavior, associative learning, motor function, epilepsy and sleep. Moreover, Grm7 knockout mice exhibit an attenuated response to amphetamine. These findings provide rationale for further investigation of mGlu₇ as a potential therapeutic target for neurodevelopmental disorders such as idiopathic autism, attention deficit hyperactivity disorder and Rett syndrome.     

Lesser Prairie-Chicken Survival in Varying Densities of Energy Development

Anthropogenic features increasingly affect ecological processes with increasing human demand for natural resources. Such effects also have the potential to vary depending on the sex and age of an individual because of inherent behavioral and life experience differences. For the lesser prairie-chicken (Tympanuchus pallidicinctus), studies on male survival are limited because most previous research has been focused on females. To better understand patterns of lesser prairie-chicken survival in habitat with varying levels of anthropogenic infrastructure associated with oil and natural gas development, we monitored survival of 178 radio-tagged male and female lesser prairie-chickens in eastern New Mexico, USA, from 2013 to 2015. We examined the relationships of shrub cover, proximity to and density of anthropogenic features (i.e., utility poles), displacement of natural vegetation by anthropogenic features (i.e., area of roads and well pads), and individual demographics (i.e., sex, age) with lesser prairie-chicken survival. Furthermore, we categorized the probable cause of mortality and examined its relationship with oil and gas development intensity (indexed by utility pole density) within 1,425 m of an individual's mortality site or final observed location. We predicted that survival would be lower for individuals exposed to greater levels of anthropogenic features, and that males and subadults would be more negatively affected than females and adults because of increased exposure to predators during the lekking season and naiveté. Relationships between survival and utility pole density, sex, and age were supported in our top-ranked models, whereas models including other anthropogenic and natural features (i.e., roads, well pads, shrub cover) received little support. We predicted a substantial decrease in adult and subadult male survival with increasing densities of utility poles. The relationship between survival and utility pole density for females was weaker and not as clearly supported as for males. We did not find a detectable difference in utility pole counts among probable mortality causes. Our findings highlight the importance of including male lesser prairie-chickens in research and conservation planning, and the negative effect that high densities of anthropogenic features can have on lesser prairie-chicken survival. © 2021 The Wildlife Society.     

Triacylglycerol Synthesis Enzymes Mediate Lipid Droplet Growth by Relocalizing from the ER to Lipid Droplets

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Highlights? Triacylglyceride (TG) synthesis is coupled with lipid droplet (LD) growth ? Two LD populations exist: growing LDs, containing TG enzymes, and small LDs ? Specific TG synthesis enzymes move from the ER to LDs through membrane bridges ? LD localization of TG enzymes mediates expansion of a subset of LDs     

A Dexamethasone Prodrug Reduces the Renal Macrophage Response and Provides Enhanced Resolution of Established Murine Lupus Nephritis

We evaluated the ability of a macromolecular prodrug of dexamethasone (P-Dex) to treat lupus nephritis in (NZB × NZW)F1 mice. We also explored the mechanism underlying the anti-inflammatory effects of this prodrug. P-Dex eliminated albuminuria in most (NZB × NZW)F1 mice. Furthermore, P-Dex reduced the incidence of severe nephritis and extended lifespan in these mice. P-Dex treatment also prevented the development of lupus-associated hypertension and vasculitis. Although P-Dex did not reduce serum levels of anti-dsDNA antibodies or glomerular immune complexes, P-Dex reduced macrophage recruitment to the kidney and attenuated tubulointerstitial injury. In contrast to what was observed with free dexamethasone, P-Dex did not induce any deterioration of bone quality. However, P-Dex did lead to reduced peripheral white blood cell counts and adrenal gland atrophy. These results suggest that P-Dex is more effective and less toxic than free dexamethasone for the treatment of lupus nephritis in (NZB × NZW)F1 mice. Furthermore, the data suggest that P-Dex may treat nephritis by attenuating the renal inflammatory response to immune complexes, leading to decreased immune cell infiltration and diminished renal inflammation and injury.     

TNF-α Acts as an Immunoregulator in the Mouse Brain by Reducing the Incidence of Severe Disease Following Japanese Encephalitis Virus Infection

Japanese encephalitis virus (JEV) causes acute central nervous system (CNS) disease in humans, in whom the clinical symptoms vary from febrile illness to meningitis and encephalitis. However, the mechanism of severe encephalitis has not been fully elucidated. In this study, using a mouse model, we investigated the pathogenetic mechanisms that correlate with fatal JEV infection. Following extraneural infection with the JaOArS982 strain of JEV, infected mice exhibited clinical signs ranging from mild to fatal outcome. Comparison of the pathogenetic response between severe and mild cases of JaOArS982-infected mice revealed increased levels of TNF-α in the brains of severe cases. However, unexpectedly, the mortality rate of TNF-α KO mice was significantly increased compared with that of WT mice, indicating that TNF-α plays a protective role against fatal infection. Interestingly, there were no significant differences of viral load in the CNS between WT and TNF-α KO mice. However, exaggerated inflammatory responses were observed in the CNS of TNF-α KO mice. Although these observations were also obtained in IL-10 KO mice, the mortality and enhanced inflammatory responses were more pronounced in TNF-α KO mice. Our findings therefore provide the first evidence that TNF-α has an immunoregulatory effect on pro-inflammatory cytokines in the CNS during JEV infection and consequently protects the animals from fatal disease. Thus, we propose that the increased level of TNF-α in severe cases was the result of severe disease, and secondly that immunopathological effects contribute to severe neuronal degeneration resulting in fatal disease. In future, further elucidation of the immunoregulatory mechanism of TNF-α will be an important priority to enable the development of effective treatment strategies for Japanese encephalitis.     

Defective Autophagy and mTORC1 Signaling in Myotubularin Null Mice

Autophagy is a vesicular trafficking pathway that regulates the degradation of aggregated proteins and damaged organelles. Initiation of autophagy requires several multiprotein signaling complexes, such as the ULK1 kinase complex and the Vps34 lipid kinase complex, which generates phosphatidylinositol 3-phosphate [PtdIns(3)P] on the forming autophagosomal membrane. Alterations in autophagy have been reported for various diseases, including myopathies. Here we show that skeletal muscle autophagy is compromised in mice deficient in the X-linked myotubular myopathy (XLMTM)-associated PtdIns(3)P phosphatase myotubularin (MTM1). Mtm1-deficient muscle displays several cellular abnormalities, including a profound increase in ubiquitin aggregates and abnormal mitochondria. Further, we show that Mtm1 deficiency is accompanied by activation of mTORC1 signaling, which persists even following starvation. In vivo pharmacological inhibition of mTOR is sufficient to normalize aberrant autophagy and improve muscle phenotypes in Mtm1 null mice. These results suggest that aberrant mTORC1 signaling and impaired autophagy are consequences of the loss of Mtm1 and may play a primary role in disease pathogenesis.     

Ca2+-dependent Structural Changes in the B-cell Receptor CD23 Increase Its Affinity for Human Immunoglobulin E

Immunoglobulin E (IgE) antibodies play a fundamental role in allergic disease and are a target for therapeutic intervention. IgE functions principally through two receptors, FcϵRI and CD23 (FcϵRII). Minute amounts of allergen trigger mast cell or basophil degranulation by cross-linking IgE-bound FcϵRI, leading to an inflammatory response. The interaction between IgE and CD23 on B-cells regulates IgE synthesis. CD23 is unique among Ig receptors in that it belongs to the C-type (calcium-dependent) lectin-like superfamily. Although the interaction of CD23 with IgE is carbohydrate-independent, calcium has been reported to increase the affinity for IgE, but the structural basis for this activity has previously been unknown. We have determined the crystal structures of the human lectin-like head domain of CD23 in its Ca²⁺-free and Ca²⁺-bound forms, as well as the crystal structure of the Ca²⁺-bound head domain of CD23 in complex with a subfragment of IgE-Fc consisting of the dimer of Cϵ3 and Cϵ4 domains (Fcϵ3-4). Together with site-directed mutagenesis, the crystal structures of four Ca²⁺ ligand mutants, isothermal titration calorimetry, surface plasmon resonance, and stopped-flow analysis, we demonstrate that Ca²⁺ binds at the principal and evolutionarily conserved binding site in CD23. Ca²⁺ binding drives Pro-250, at the base of an IgE-binding loop (loop 4), from the trans to the cis configuration with a concomitant conformational change and ordering of residues in the loop. These Ca²⁺-induced structural changes in CD23 lead to additional interactions with IgE, a more entropically favorable interaction, and a 30-fold increase in affinity of a single head domain of CD23 for IgE. Taken together, these results suggest that binding of Ca²⁺ brings an extra degree of modulation to CD23 function.