TFEB

Glucocerebrosidase (GBA1) mutations are associated with Gaucher disease (GD), an autosomal recessive disorder caused by functional deficiency of glucocerebrosidase (GBA), a lysosomal enzyme that hydrolyzes glucosylceramide to ceramide and glucose. Neuronopathic forms of GD can be associated with rapid neurological decline (Type II) or manifest as a chronic form (Type III) with a wide spectrum of neurological signs. Furthermore, there is now a well-established link between GBA1 mutations and Parkinson's disease (PD), with heterozygote mutations in GBA1 considered the commonest genetic defect in PD. Here we describe a novel Drosophila model of GD that lacks the two fly GBA1 orthologs. This knockout model recapitulates the main features of GD at the cellular level with severe lysosomal defects and accumulation of glucosylceramide in the fly brain. We also demonstrate a block in autophagy flux in association with reduced lifespan, age-dependent locomotor deficits and accumulation of autophagy substrates in dGBA-deficient fly brains. Furthermore, mech-anistic target of rapamycin (mTOR) signaling is downregulated in dGBA knockout flies, with a concomitant upregulation of Mitf gene expression, the fly ortholog of mammalian TFEB, likely as a compensatory response to the autophagy block. Moreover, the mTOR inhibitor rapamycin is able to partially ameliorate the lifespan, locomotor, and oxidative stress phenotypes. Together, our results demonstrate that this dGBA1-deficient fly model is a useful platform for the further study of the role of lysosomal-autophagic impairment and the potential therapeutic benefits of rapamycin in neuronopathic GD. These results also have important implications for the role of autophagy and mTOR signaling in GBA1-associated PD.

<p>Changes in expression of <i>srh-234</i> are directed by multiple cell-autonomous and non-cell-autonomous transcriptional modules. In ADL neurons, one module consists of a MEF-2 transcription factor and its MEF2 binding site, and the other module consists of a bHLH heterodimer (e.g. HLH-2/3, and HLH-2/4) and its bi-partite E-box binding site. When fed <b>(A)</b>, MEF-2 activity is low and is prevented from repressing HLH-2/3/4 factors, and expression of <i>srh-234</i> in ADL is increased. When starved <b>(B)</b>, MEF-2 is no longer inhibited, allowing binding to the MEF2 site in <i>srh-234</i> (AGTTATATTTAA), which in turn represses HLH-2/3/4-mediated activation of <i>srh-234</i> at the E-box site (CACCTG), ultimately leading to the decrease in <i>srh-234</i> expression. In addition to cell-autonomous mechanisms, the bHLH factors MXL-3 and HLH-30 act in the intestine to remotely regulate changes in <i>srh-234</i> expression via the DAF-2/DAF-16 insulin pathway acting in ADL. When fed <b>(A)</b>, MXL-3 activity is high in the intestine (low HLH-30 activity) and increases <i>srh-234</i> expression, whereas when starved <b>(B)</b>, HLH-30 activity is high in the intestine (low MXL-3 activity) and represses the expression of <i>srh-234</i> in ADL. The combined action of ILPs from different tissues (the intestine) and other neurons (e.g. ASE) regulated by <i>mxl-3</i>-dependent (e.g. <i>ins-3</i>, <i>ins-26</i>) or independent mechanisms results in either high or low DAF-2 activity, which in turn modulates <i>srh-234</i> expression in ADL.</p