Biology subjects

Schwake, M.

Publications and source records attributed to Schwake, M..

5 recordsLinked to original sources

bioRxiv2020

Bi-allelic variants in TSPOAP1, encoding the active zone protein RIMBP1, cause autosomal recessive dystonia

Dystonia is a debilitating hyperkinetic movement disorder, frequently transmitted as a monogenic trait. Here, we describe homozygous frameshift, nonsense and missense variants in TSPOAP1, encoding the active zone RIM-binding protein 1 (RIMBP1), as a novel genetic cause of autosomal recessive dystonia in seven subjects from three unrelated families. Subjects carrying loss-of-function variants presented with juvenile- onset progressive generalized dystonia, associated with intellectual disability and cerebellar atrophy. Conversely, subjects carrying a pathogenic missense variant (p.Gly1808Ser) presented with isolated adult-onset focal dystonia. In mice, complete loss of RIMBP1, known to reduce neurotransmission, led to motor abnormalities reminiscent of dystonia, decreased Purkinje cell dendritic arborization, and reduced numbers of cerebellar synapses. In vitro analysis of the p.Gly1808Ser variant showed larger spike-evoked calcium transients and enhanced neurotransmission, suggesting that RIMBP1-linked dystonia can be caused by either reduced or enhanced rates of spike-evoked release in relevant neural networks. Our findings establish a direct link between presynaptic RIMBP1 dysfunction and dystonia and highlight the critical role played by well-balanced neurotransmission in motor control and disease pathogenesis.

genetics↗

bioRxiv2019

Aging is associated with a systemic length-driven transcriptome imbalance

Aging manifests itself through a decline in organismal homeostasis and a multitude of cellular and physiological functions1. Efforts to identify a common basis for vertebrate aging face many challenges; for example, while there have been documented changes in the expression of many hundreds of mRNAs, the results across tissues and species have been inconsistent2. We therefore analyzed age-resolved transcriptomic data from 17 mouse organs and 51 human organs using unsupervised machine learning3-5 to identify the architectural and regulatory characteristics most informative on the differential expression of genes with age. We report a hitherto unknown phenomenon, a systemic age-dependent length-driven transcriptome imbalance that for older organisms disrupts the homeostatic balance between short and long transcript molecules for mice, rats, killifishes, and humans. We also demonstrate that in a mouse model of healthy aging, length-driven transcriptome imbalance correlates with changes in expression of splicing factor proline and glutamine rich (Sfpq), which regulates transcriptional elongation according to gene length6. Furthermore, we demonstrate that length-driven transcriptome imbalance can be triggered by environmental hazards and pathogens. Our findings reinforce the picture of aging as a systemic homeostasis breakdown and suggest a promising explanation for why diverse insults affect multiple age-dependent phenotypes in a similar manner.

systems biology↗

bioRxiv2019

Impaired M-current in KCNQ2 Encephalopathy Evokes Dyshomeostatic Modulation of Excitability

Mutations in KCNQ2, which encodes a pore-forming K+ channel subunit responsible for neuronal M-current, cause neonatal epileptic encephalopathy, a complex disorder presenting with severe early-onset seizures and impaired neurodevelopment. The condition is exceptionally difficult to treat, partially because the effects of KCNQ2 mutations on the development and function of human neurons are unknown. Here, we used induced pluripotent stem cells and gene editing to establish a disease model, and measured the functional properties of patient-derived neurons using electrophysiological and optical approaches. We find that while patient-derived excitatory neurons exhibit reduced M-current early, they develop intrinsic and network hyperexcitability progressively. This hyperexcitability is associated with faster action potential repolarization, larger afterhyperpolarization, and a functional enhancement of large conductance Ca2+-activated K+ (BK) channels. These properties facilitate a burst-suppression firing pattern that is reminiscent of the interictal electroencephalography pattern in patients. Importantly, we were able to phenocopy these excitability features in control neurons only by chronic but not acute pharmacological inhibition of M-current. Our findings suggest that dyshomeostatic mechanisms compound KCNQ2 loss-of-function and lead to alterations in the neurodevelopmental trajectory of patient-derived neurons. Our work has therapeutic implications in explaining why KCNQ2 agonists are not beneficial unless started at an early disease stage.

neuroscience↗

bioRxiv2019

A DNA-based voltmeter for organelles

The role of membrane potential in most intracellular organelles remains unexplored because of the lack of suitable probes. We describe a DNA-based fluorescent reporter that quantitates membrane potential and can be targeted to specific organelles in live cells. It is equipped with a voltage sensitive fluorophore, a reference fluorophore for ratiometric quantification, and acts as an endocytic tracer. We could thereby measure the membrane potential of different intracellular organelles in living cells, which has not been possible previously. Our understanding of how membrane potential regulates organelle biology is poised to expand through the use of these new sensors.\n\nOne Sentence SummaryUsing a DNA-based voltmeter we can non-invasively measure the membrane potential of specific organelles in live cells.

biophysics↗

bioRxiv2018

Doxorubicin induces caspase-mediated proteolysis of KV7.1

The voltage-gated potassium channel Kv7.1 (KCNQ1) co-assembles with KCNE1 to generate the cardiac potassium current IKs. Gain- and loss-of-function mutations in KCNQ1 are associated with atrial fibrillation and long-QT (LQT) syndrome, respectively, highlighting the importance of modulating IKS activity for proper cardiac function. On a post-translational level, IKS can be regulated by phosphorylation, ubiquitination and sumoylation. Here, we report proteolysis of Kv7.1 as a novel, irreversible posttranslational modification. The identification of two C-terminal fragments (CTF1 and CTF2) of Kv7.1 led us to identify an aspartate critical for the generation of CTF2 and caspases as responsible for mediating Kv7.1 proteolysis. Activating caspases by apoptotic stimuli significantly reduced Kv7.1/KCNE1 currents, which was abrogated in cells expressing caspase-resistant Kv7.1 D459A/KCNE1 channels. An increase in cleavage of Kv7.1 could be detected in the case of LQT mutation G460S, which is located adjacent to the cleavage site. Application of apoptotic stimuli or doxorubicin-induced cardiotoxicity provoked caspase-mediated cleavage of endogenous Kv7.1 in human cardiomyocytes. In summary, our findings establish caspases as novel regulatory components for modulating Kv7.1 activity which may have important implications for the molecular mechanism of doxorubicin-induced cardiotoxicity.\n\nNon-standard Abbreviations and Acronyms

biochemistry↗