Biology subjects

Kahle, P. J.

Publications and source records attributed to Kahle, P. J..

4 recordsLinked to original sources

bioRxiv2025

Parkin-dependent ubiquitination of TAX1BP1 directs efficient autophagic removal of defective mitochondria

In stressed cells, the recessive Parkinson disease (PD) associated gene products PINK1 and parkin mediate the autophagic removal of damaged mitochondria (mitophagy). Upon mitochondrial membrane potential disruption, PINK1 phosphorylation activates the ubiquitin ligase parkin which ubiquitinates various mitochondrial protein substrates. These feed-forward modifications on the mitochondria surface attract ubiquitin-binding autophagy receptors that target ubiquitinated mitochondria for degradation. Investigating post-translational protein modifications during this process, we detected transient ubiquitination of K549 within the third coiled-coil domain (CC3) of TAX1BP1 in HeLa cells expressing wild-type (WT) but not catalytically inactive parkin. Parkin-dependent ubiquitination did not target TAX1BP1 to proteasomal degradation but was rather indicative of a regulatory modification. In cells with the full complement of autophagy receptors, TAX1BP1 plays only a minor role in mitophagy. However, when expressed as a sole autophagy receptor, both WT and ubiquitination deficient TAX1BP1 were capable of promoting mitophagy, albeit mitochondria degradation was slightly delayed under mutant conditions. Use of the lysosomal inhibitor bafilomycin A indicated classical autophagolysosomal targeting of damaged mitochondria mediated by WT TAX1BP1. However, for the ubiquitination-deficient TAX1BP1, we observed an increased prevalence of enlarged endolysosomal vesicles carrying accumulated TAX1BP1-positive autophagosomes filled with mitochondrial material. Thus, while ubiquitination of the CC3 domain of TAX1BP1 is not essential for complete mitophagy, the lack of CC3 in TAX1BP1 reroutes the degradation flux to a less efficient endolysosmal degradative pathway. Interestingly, the PD gene product VPS35 becomes prominently engaged in this alternative mitophagy pathway.

cell biology↗

bioRxiv2021

LAG3 is not expressed in human and murine neurons and does not modulate α-synucleinopathies

While the initial pathology of Parkinsons disease and other -synucleinopathies is often confined to circumscribed brain regions, it can spread and progressively affect adjacent and distant brain locales. This process may be controlled by cellular receptors of -synuclein fibrils, one of which was proposed to be the LAG3 immune checkpoint molecule. Here, we analyzed the expression pattern of LAG3 in human and mouse brains. Using a variety of methods and model systems, we found no evidence for LAG3 expression by neurons. While we confirmed that LAG3 interacts with -synuclein fibrils, the specificity of this interaction appears limited. Moreover, overexpression of LAG3 in cultured human neural cells did not cause any worsening of -synuclein pathology ex vivo. The overall survival of A53T -synuclein transgenic mice was unaffected by LAG3 depletion and the seeded induction of -synuclein lesions in hippocampal slice cultures was unaffected by LAG3 knockout. These data suggest that the proposed role of LAG3 in the spreading of -synucleinopathies is not universally valid.

neuroscience↗

bioRxiv2020

Lysine acetylation of TDP-43 drives phase separation and pathological aggregation

The trans-activation response DNA-binding protein TDP-43 regulates RNA processing and forms neuropathological aggregates in patients with amyotrophic lateral sclerosis and frontotemporal lobar degeneration. Investigating TDP-43 post-translational modifications, we discovered that K84 acetylation reduced nuclear import whereas K136 acetylation impaired RNA binding and splicing capabilities of TDP-43. Such failure of RNA interaction triggered TDP-43 phase separation mediated by the C-terminal low complexity domain, leading to the formation of insoluble aggregates with pathologically phosphorylated and ubiquitinated TDP-43. Confirming the results from site-directed mutagenesis, we succeeded to introduce authentic acetyl-lysine at the identified sites via amber suppression. [AcK84]TDP-43 showed cytoplasmic mislocalization and the aggregation propensity of [acK136]TDP-43 was confirmed. With newly developed antibodies, we found that the nuclear sirtuin SIRT1 can potently deacetylate [acK136]TDP-43. Moreover, SIRT1 reduced the aggregation propensity of [acK136]TDP-43. Thus, distinct lysine acetylations modulate nuclear import, RNA binding and phase separation of TDP-43, suggesting novel regulatory mechanisms for TDP-43 pathogenesis.

cell biology↗

bioRxiv2019

PINK1 Regulates Dopamine and Lipids at Mitochondria to Maintain Synapses and Neuronal Function

Mitochondrial dysfunction contributes to the pathogenesis of Parkinsons disease but it is not clear why inherent mitochondrial defects lead specifically to the death of dopaminergic neurons of the mid brain. PINK1 is mitochondrial kinase and PINK1 mutations cause early onset Parkinsons disease.\n\nWe found that in neuronal progenitors, PINK1 regulates mitochondrial morphology, mitochondrial contact to the endoplasmic reticulum (ER) and the phosphorylation of Miro1. A compensatory metabolic shift towards lipid synthesis provides mitochondria with the components needed for membrane renewal and oxidative phosphorylation, maintaining the mitochondrial network once mature.\n\nCholesterol is increased by loss of PINK1, promoting overall membrane rigidity. This alters the distribution of phosphorylated DAT at synapses and impairs dopamine uptake. PINK1 is required for the phosphorylation of tyrosine hydroxylase at Ser19, dopamine and calcium homeostasis and dopaminergic pacemaking.\n\nWe suggest a novel mechanism for PINK1 pathogenicity in Parkinsons disease in addition to but not exclusive of mitophagy. We also provide a basis for potential therapeutics by showing that low doses of the cholesterol depleting drug {beta}-cyclodextrin reverse PINK1-specific phenotypes.

neuroscience↗