Zebrafish TARP Cacng2 is required for the expression and normal development of AMPA receptors at excitatory synapses

Dietary choline intake is necessary to prevent systems-wide organ pathology and reduce Alzheimer's disease hallmarks

There is an urgent need to identify modifiable environmental risk factors that reduce the incidence of Alzheimer's disease (AD). The B-like vitamin choline plays key roles in body- and brain-related functions. Choline produced endogenously by the phosphatidylethanolamine N-methyltransferase protein in the liver is not sufficient for adequate physiological functions, necessitating daily dietary intake. ~90% of Americans do not reach the recommended daily intake of dietary choline. Thus, it's imperative to determine whether dietary choline deficiency increases disease outcomes. Here, we placed 3xTg-AD, a model of AD, and non-transgenic (NonTg) control mice on either a standard laboratory diet with sufficient choline (ChN; 2.0 g/kg choline bitartrate) or a choline-deficient diet (Ch-; 0.0 g/kg choline bitartrate) from 3 to 12 (early to late adulthood) months of age. A Ch- diet reduced blood plasma choline levels, increased weight, and impaired both motor function and glucose metabolism in NonTg mice, with 3xTg-AD mice showing greater deficits. Tissue analyses showed cardiac and liver pathology, elevated soluble and insoluble Amyloid-β and Thioflavin S structures, and tau hyperphosphorylation at various pathological epitopes in the hippocampus and cortex of 3xTg-AD Ch- mice. To gain mechanistic insight, we performed unbiased proteomics of hippocampal and blood plasma samples. Dietary choline deficiency altered hippocampal networks associated with microtubule function and postsynaptic membrane regulation. In plasma, dietary choline deficiency altered protein networks associated with insulin metabolism, mitochondrial function, inflammation, and fructose metabolic processing. Our data highlight that dietary choline intake is necessary to prevent systems-wide organ pathology and reduce hallmark AD pathologies.

Expression and Development of TARP γ-4 in Embryonic Zebrafish

Fast excitatory synaptic transmission in the CNS is mediated by the neurotransmitter glutamate, binding to and activating AMPA receptors (AMPARs). AMPARs are known to interact with auxiliary proteins that modulate their behavior. One such family of proteins is the transmembrane AMPAR-related proteins, known as TARPs. Little is known about the role of TARPs during development or about their function in nonmammalian organisms. Here, we report on the presence of TARP γ-4 in developing zebrafish. We find that zebrafish express 2 forms of TARP γ-4: γ-4a and γ-4b as early as 12 h post-fertilization. Sequence analysis shows that both γ-4a and γ-4b shows great level of variation particularly in the intracellular C-terminal domain compared to rat, mouse, and human γ-4. RT-qPCR showed a gradual increase in the expression of γ-4a throughout the first 5 days of development, whereas γ-4b levels were constant until day 5 when levels increased significantly. Knockdown of TARP γ-4a and γ-4b via either splice-blocking morpholinos or translation-blocking morpholinos resulted in embryos that exhibited deficits in C-start escape responses, showing reduced C-bend angles. Morphant larvae displayed reduced bouts of swimming. Whole-cell patch-clamp recordings of AMPAR-mediated currents from Mauthner cells showed a reduction in the frequency of mEPCs but no change in amplitude or kinetics. Together, these results suggest that γ-4a and γ-4b are required for proper neuronal development.

Impaired AMPA receptor trafficking by a double knockout of zebrafish olfactomedin1a/b

The olfm1a and olfm1b genes in zebrafish encode conserved secreted glycoproteins. These genes are preferentially expressed in the brain and retina starting from 16 h post-fertilization until adulthood. Functions of the Olfm1 gene is still unclear. Here, we produced and analyzed a null zebrafish mutant of both olfm1a and olfm1b genes (olfm1 null). olfm1 null fish were born at a normal Mendelian ratio and showed normal body shape and fertility as well as no visible defects from larval stages to adult. Olfm1 proteins were preferentially localized in the synaptosomes of the adult brain. Olfm1 co-immunoprecipitated with GluR2 and soluble NSF attachment protein receptor complexes indicating participation of Olfm1 in both pre- and post-synaptic events. Phosphorylation of GluR2 was not changed while palmitoylation of GluR2 was decreased in the brain synaptosomal membrane fraction of olfm1 null compared with wt fish. The levels of GluR2, SNAP25, flotillin1, and VAMP2 were markedly reduced in the synaptic microdomain of olfm1 null brain compared with wt. The internalization of GluR2 in retinal cells and the localization of VAMP2 in brain synaptosome were modified by olfm1 null mutation. This indicates that Olfm1 may regulate receptor trafficking from the intracellular compartments to the synaptic membrane microdomain, partly through the alteration of post-translational GluR2 modifications such as palmitoylation. Olfm1 may be considered a novel regulator of the composition and function of the α-amino-3-hydroxy-5-methylisoxazole-4-propionate receptor complex.

Using the shared genetics of dystonia and ataxia to unravel their pathogenesis

In this review we explore the similarities between spinocerebellar ataxias and dystonias, and suggest potentially shared molecular pathways using a gene co-expression network approach. The spinocerebellar ataxias are a group of neurodegenerative disorders characterized by coordination problems caused mainly by atrophy of the cerebellum. The dystonias are another group of neurological movement disorders linked to basal ganglia dysfunction, although evidence is now pointing to cerebellar involvement as well. Our gene co-expression network approach identified 99 shared genes and showed the involvement of two major pathways: synaptic transmission and neurodevelopment. These pathways overlapped in the two disorders, with a large role for GABAergic signaling in both. The overlapping pathways may provide novel targets for disease therapies. We need to prioritize variants obtained by whole exome sequencing in the genes associated with these pathways in the search for new pathogenic variants, which can than be used to help in the genetic counseling of patients and their families.