Maternal immune activation alters fetal and neonatal microglia phenotype and disrupts neurogenesis in mice

BACKGROUND

Activation of microglia, increase in cortical neuron density, and reduction in GABAergic interneurons are some of the key findings in postmortem autism spectrum disorders (ASD) subjects. The aim of this study was to investigate how maternal immune activation (MIA) programs microglial phenotypes and abnormal neurogenesis in offspring mice.

METHODS

MIA was induced by injection of lipopolysaccharide (LPS, i.p.) to pregnant mice at embryonic (E) day 12.5. Microglial phenotypes and neurogenesis were investigated between E15.5 to postnatal (P) day 21 by immunohistochemistry, flow cytometry, and cytokine array.

RESULTS

MIA led to a robust increase in fetal and neonatal microglia in neurogenic regions. Homeostatic E15.5 and P4 microglia are heterogeneous, consisting of M1 (CD86+/CD206-) and mixed M1/M2 (CD86+/CD206+)-like subpopulations. MIA significantly reduced M1 but increased mixed M1/M2 microglia, which was associated with upregulation of numerous cytokines with pleotropic property. MIA resulted in a robust increase in Ki67+/Nestin+ and Tbr2+ neural progenitor cells in the subventricular zone (SVZ) of newborn mice. At juvenile stage, a male-specific reduction of Parvalbumin+ but increase in Reelin+ interneurons in the medial prefrontal cortex was found in MIA offspring mice.

CONCLUSIONS

MIA programs microglia towards a pleotropic phenotype that may drive excessive neurogenesis in ASD patients.

IMPACT

Maternal immune activation (MIA) alters microglial phenotypes in the brain of fetal and neonatal mouse offspring. MIA leads to excessive proliferation and overproduction of neural progenitors in the subventricular zone (SVZ). MIA reduces parvalbumin+ while increases Reelin+ interneurons in the prefrontal cortex. Our study sheds light on neurobiological mechanisms of abnormal neurogenesis in certain neurodevelopmental disorders, such as autism spectrum disorder (ASD).

Role of the NRG1/ErbB4 and PI3K/AKT/mTOR signaling pathways in the anti-psychotic effects of aripiprazole and sertindole in ketamine-induced schizophrenia-like behaviors in rats

Schizophrenia is a common mental disorder affecting patients' thoughts, behavior, and cognition. Recently, the NRG1/ErbB4 signaling pathway emerged as a candidate therapeutic target for schizophrenia. This study investigates the effects of aripiprazole and sertindole on the NRG1/ErbB4 and PI3K/AKT/mTOR signaling pathways in ketamine-induced schizophrenia in rats. Young male Wistar rats received ketamine (30 mg/kg, intraperitoneally) for 5 consecutive days and aripiprazole (3 mg/kg, orally) or sertindole (2.5 mg/kg, orally) for 14 days. The proposed pathway was investigated by injecting LY294002 (a selective PI3K inhibitor) (25 μg/kg, intrahippocampal injection) 30 min before the drugs. Twenty-four hours after the last injection, animals were subjected to behavioral tests: the open field test, sucrose preference test, novel object recognition task, and social interaction test. Both aripiprazole and sertindole significantly ameliorated ketamine-induced schizophrenic-like behavior, as expected, because of their previously demonstrated antipsychotic activity. Besides, both drugs alleviated ketamine-induced oxidative stress and neurotransmitter level changes in the hippocampus. They also increased the gamma-aminobutyric acid and glutamate levels and glutamate decarboxylase 67 and parvalbumin mRNA expression in the hippocampus. Moreover, aripiprazole and sertindole increased the NRG1 and ErbB4 mRNA expression levels and PI3K, p-Akt, and mTOR protein expression levels. Interestingly, pre-injecting LY294002 abolished all the effects of the drugs. This study reveals that the antipsychotic effects of aripiprazole and sertindole are partly due to oxidative stress reduction as well as NRG1/ErbB4 and PI3K/AKT/mTOR signaling pathways activation. The NRG1/ErbB4 and PI3K signaling pathways may offer a new therapeutic approach for treating schizophrenia in humans.

Purification and characterization of parvalbumin isotypes from grass carp (Ctenopharyngodon idella)

The prevalence of fish allergy is rapidly increasing because of a growing fish consumption driven mainly by a positive image of the fish and health relationship. The purpose of this study was to characterize parvalbumin isotypes from grass carp (Ctenopharyngodon idella), one of the most frequently consumed freshwater fish in China. Three parvalbumin isotypes were purified using consecutive gel filtration and reverse-phase chromatography and denoted as PVI, PVII, and PVIII. The molecular weights of the isotypes were determined to be 11.968, 11.430, and 11.512 kDa, respectively. PVI showed 74% matched amino acids sequence with PV isotype 4a from Danio rerio, while PVII and PVIII showed 46% matched amino acids sequence with PV isotypes from Hypophthalmichthys molitrix. PVII is the dominant allergen, but it was liable to gastrointestinal enzymes as PVIII; however, PVI was resistant to pepsin digestion. A further study is to characterize the epitopes of PVII, the dominant allergen.

[Cross reactivity between fish and shellfish]

In Spain, fish allergy represents 18 % of all cases of food allergy in children while reactions caused by crustacea and mollusks account for 3.8 % and 1.6 % respectively. Cross-reactivity is defined as the recognition of distinct antigens by the same IgE antibody, demonstrable by in vivo and in vitro tests, which clinically manifests as reactions caused by antigens homologous to different species. Subclinical sensitization can also occur, giving rise to patients sensitized to particular fish or shellfish but who do not present symptoms on consumption.Cod and shrimp have been the models used to study allergy to fish and crustacea respectively. The major allergens responsible for cross-reactivity among distinct species of fish and amphibians are proteins that control calcium flow in the muscular sarcoplasm of these animals, called parvalbumins, with a molecular weight of approximately 12 kD and an isoelectric point of 4.75, resistant to the action of heat and enzymatic digestion. Recently, recombinant carp parvalbumin has been reproduced, confirming that this allergen contains 70 % of the IgE epitopes present in natural extract of cod, tuna and salmon, which makes it a valid tool in the diagnosis of patients with fish allergy. Moreover, this recombinant allergen could constitute the basis for the development of immunotherapy against food allergy. In the case of shellfish, a non-taxonomic group that includes crustacea and mollusks, the major allergen is tropomyosin, an essential protein in muscle contraction both in invertebrates and vertebrates. In invertebrates, tropomyosins, which have a molecular weight of between 38 and 41 kD, show great homology in their amino acid sequence and are the panallergens responsible for cross-reactions between crustacea, insects, mites, nematodes, and different classes of mollusks. It is estimated that 50 % of individuals allergic to some type of fish are at risk for reacting to a second species, while those allergic to some type of crustacea present a risk of 75 % due to the greater similarity among tropomyosins than among parvalbumins. In addition, up to 40 % of patients sensitized to one or more fish do not present symptoms on consuming other species, the best tolerated of which belong to the Scombroidea family (which includes tuna).

Purification, biochemical, and immunological characterisation of a major food allergen: different immunoglobulin E recognition of the apo- and calcium-bound forms of carp parvalbumin

BACKGROUND

Almost 4% of the population suffer from food allergy which is an adverse reaction to food with an underlying immunological mechanism.

AIMS

To characterise one of the most frequent IgE defined food allergens, fish parvalbumin.

METHODS

Tissue and subcellular distribution of carp parvalbumin was analysed by immunogold electron microscopy and cell fractionation. Parvalbumin was purified to homogeneity, analysed by mass spectrometry and circular dichroism (CD) spectroscopy, and its allergenic activity was analysed by IgE binding and basophil histamine release tests.

RESULTS

The isoelectric point (pI) 4.7 form of carp parvalbumin, a three EF-hand calcium-binding protein, was purified to homogeneity. CD analysis revealed a remarkable stability and refolding capacity of calcium-bound parvalbumin. This may explain why parvalbumin, despite cooking and exposure to the gastrointestinal tract, can sensitise patients. Purified parvalbumin reacted with IgE of more than 95% of individuals allergic to fish, induced dose-dependent basophil histamine release and contained, on average, 83% of the IgE epitopes present in other fish species. Calcium depletion reduced the IgE binding capacity of parvalbumin which, according to CD analysis, may be due to conformation-dependent IgE recognition.

CONCLUSIONS

Purified carp parvalbumin represents an important cross reactive food allergen. It can be used for in vitro and in vivo diagnosis of fish-induced food allergy. Our finding that the apo-form of parvalbumin had a greatly reduced IgE binding capacity indicates that this form may be a candidate for safe immunotherapy of fish-related food allergy.