Biology subjects

Kittler, J. T.

Publications and source records attributed to Kittler, J. T..

4 recordsLinked to original sources

bioRxiv2018

Miro ubiquitination is critical for efficient damage-induced PINK1/Parkin-mediated mitophagy

Clearance of mitochondria following damage is critical for neuronal homeostasis. Here, we investigate the role of Miro proteins in mitochondrial turnover by the PINK1 / Parkin mitochondrial quality control system in vitro and in vivo. We find that upon mitochondrial damage, Miro is promiscuously ubiquitinated on multiple lysine residues. Combined knockout of both Miro1 and Miro2 or block of Miro ubiquitination and subsequent degradation, lead to slowed mitophagy. In cultured neurons, Miro1 knockout also leads to delayed Parkin translocation onto damaged mitochondria and reduced mitochondrial clearance. In vivo, postnatal knockout of Miro1 in hippocampus and cortex disrupts mitophagy and leads to a dramatic age dependent upregulation of the mitofusin mitochondrial fusion machinery. Fluorescence imaging of aged neurons conditionally knocked out for Miro1 and expressing mitoDendra to label mitochondria in vivo, reveals that Mfn1 / Mfn2 upregulation leads to enlarged and hyperfused somatic mitochondria. Our results provide new insights into the role of Miro in PINK1/Parkin dependent mitophagy and further suggest that disruption of this regulation may be implicated in human neurological pathology.

neuroscience↗

bioRxiv2018

Correct CYFIP1 dosage is essential for synaptic inhibition and the excitatory/inhibitory balance.

Altered excitatory/inhibitory balance is implicated in neuropsychiatric disorders but the genetic aetiology of this is still poorly understood. Copy number variations in CYFIP1 are associated with autism, schizophrenia and intellectual disability but the role of CYFIP1 in regulating synaptic inhibition or excitatory/inhibitory balance remains unclear. We show, CYFIP1, and its paralogue CYFIP2, are enriched at inhibitory postsynaptic sites. While upregulation of CYFIP1 or CYFIP2 increased excitatory synapse number and the frequency of miniature excitatory postsynaptic currents (mEPSCs), it had the opposite effect at inhibitory synapses, decreasing their size and the amplitude of miniature inhibitory postsynaptic currents (mIPSCs). Contrary to CYFIP1 upregulation, its loss in vivo, upon conditional knockout in neocortical principal cells, increased expression of postsynaptic GABAA receptor {beta}2/3-subunits and neuroligin 3 and enhanced synaptic inhibition. Thus, CYFIP1 dosage can bi-directionally impact inhibitory synaptic structure and function, potentially leading to altered excitatory/inhibitory balance and circuit dysfunction in CYFIP1-associated neurodevelopmental disorders.

neuroscience↗

bioRxiv2017

The mitochondrial Rho-GTPase, Miro, is resident at peroxisomes and regulates peroxisomal trafficking and morphology

Peroxisomes are essential for a number of cellular functions, including reactive oxygen species metabolism, fatty acid {beta}-oxidation and lipid biosynthesis. To ensure optimal functionality of peroxisome-dependent processes throughout the cell they must be trafficked; however, peroxisomal transport remains poorly characterised. Here we show that Miro1 and Miro2, outer mitochondrial membrane proteins essential for mitochondrial trafficking, are also localised to peroxisomes. Peroxisomal localisation of Miro1 is negatively regulated by its first GTPase domain and is mediated by an interaction through its transmembrane domain with the peroxisomal-membrane protein chaperone, Pex19. By using Miro1/2 double knockout mouse embryonic fibroblasts (MEFs) we find that the loss of Miro1/2 leads to a significant reduction in short-range microtubule-independent peroxisomal motility. Additionally, Miro regulates peroxisomal size and morphology. Our results contribute to the fundamental understanding of peroxisomal trafficking and morphology, supporting a complex crosstalk between peroxisomal and mitochondrial biology.

cell biology↗

bioRxiv2017

AP-4 mediated ATG9A sorting underlies axonal and autophagosome biogenesis defects in a mouse model of AP-4 deficiency syndrome

Adaptor protein (AP) complexes have critical roles in transmembrane protein sorting. AP-4 remains poorly understood in the brain despite its loss of function leading to a hereditary spastic paraplegia termed AP-4 deficiency syndrome. Here we demonstrate that knockout (KO) of AP-4 in a mouse model leads to thinning of the corpus callosum and ventricular enlargement, anatomical defects previously described in patients. At the cellular level, we find that AP-4 KO leads to defects in axonal extension and branching, in addition to aberrant distal swellings. Interestingly, we show that ATG9A, a key protein in autophagosome maturation, is critically dependent on AP-4 for its sorting from the trans-golgi network. Failure of AP-4 mediated ATG9A sorting results in its dramatic retention in the trans-golgi network in vitro and in vivo leading to a specific reduction of the axonal pool of ATG9A. As a result, autophagosome biogenesis is aberrant in the axon of AP-4 deficient neurons. The specific alteration to axonal integrity and axonal autophagosome maturation in AP-4 knockout neurons may underpin the pathology of AP-4 deficiency.

neuroscience↗