Distinct Retinal Deficits in a Zebrafish Pyruvate Dehydrogenase-Deficient Mutant

Abstract

Mutations in ubiquitously expressed metabolic genes often lead to CNS-specific effects, presumably because of the high metabolic demands of neurons. However, mutations in omnipresent metabolic pathways can conceivably also result in cell type-specific effects because of cell-specific requirements for intermediate products. One such example is the zebrafish noir mutant, which we found to be mutated in the pdhb gene, coding for the E1 ␤ subunit of the pyruvate dehydrogenase complex. This vision mutant is described as blind and was isolated because of its vision defect-related darker appearance. A detailed morphological, behavioral, and physiological analysis of the phenotype revealed an unexpected specific effect on the retina. Surprisingly, the cholinergic amacrine cells of the inner retina are affected earlier than the photoreceptors. This might be attributable to the inability of these cells to maintain production of their neurotransmitter acetylcholine. This is reflected in an earlier loss of motion vision, followed only later by a general loss of light perception. Since both characteristics of the phenotype are attributable to a loss of acetyl-CoA production by pyruvate dehydrogenase, we used a ketogenic diet to bypass this metabolic block and could indeed partially rescue vision and prolong survival of the larvae. The noir mutant provides a case for a systemic disease with ocular manifestation with a surprising specific effect on the retina given the ubiquitous requirement for the mutated gene.

mglur6b:EGFP Transgenic zebrafish suggest novel functions of metabotropic glutamate signaling in retina and other brain regions

“…The ChAT antibody recognized only a band of around 70 kD on Western blots of mouse brain lysate (manufacturer's information at www.merckmillipore.com), and stained a pattern of cellular morphology and distribution consistent with amacrine cell labeling, identical to previous reports from the teleost retina (Yazulla and Studholme, 2001;Maurer et al, 2010).…”

“…The TH antibody recognized only a band of around 60 kD on Western blots of cell lysates (manufacturer's datasheet), and stained a pattern of cellular morphology and location in the zebrafish retina identical to previous reports using another TH antibody (Maurer et al, 2010).…”

Probing Metabolism in the Intact Retina Using Stable Isotope Tracers

“…Retinal degenerative diseases have been linked to mutations in energy metabolism and purine metabolism such as isocitrate dehydrogenase 3b, pyruvate dehydrogenase E1/2, nicotinamide mononucleotide adenylyltransferase, inosine monophosphate dehydrogenase, phosphodiesterase 6, and guanylyl cyclase (Aherne et al, 2004; Dizhoor, Boikov, & Olshevskaya, 1998; Farber & Lolley, 1974; Hartong et al, 2008; Maurer et al, 2010; Perrault et al, 2012; Taylor, Hurley, Van Epps, & Brockerhoff, 2004). Disruption of nutrient availability and metabolic regulation might play important roles in AMD and several models of retinitis pigmentosa (Punzo, Kornacker, & Cepko, 2009; Umino et al, 2006).…”

“…Removal of glucose, inhibition of glycolysis, or deprivation of oxygen rapidly diminishes the ability of the retina to respond to light (Ames et al, 1992; Kang Derwent & Linsenmeier, 2000). Deficiencies of key enzymes and transporters in glucose metabolism cause retinal degeneration (Bui, Kalloniatis, & Vingrys, 2004; Maurer, Schonthaler, Mueller, & Neuhauss, 2010; Ochrietor & Linser, 2004). Neurons in the retina require metabolic support from glial cells.…”

The serotonergic system in fish

“…Furthermore, in a few studies using Xenopus or skate (Raja erinacea), it has been shown that bipolar neurons can take up 5-HT (Schuette and Chappell, 1998;Schü tte, 1994). In the retina of zebrafish 5-HTimmunoreactive cells have also been detected among the amacrine population (Avanesov et al, 2005;Maurer et al, 2010). This domain contains cells with transcripts for tph1a, sertb, htr1aa, aanat1 and/or 2 (Bellipanni et al, 2002;Coon et al, 1999;Falcon et al, 2003;Norton et al, 2008;Zilberman-Peled et al, 2004).…”