Piezo buffers mechanical stress via modulation of intracellular Ca2+ handling in the Drosophila heart.

Throughout its lifetime the heart is buffeted continuously by dynamic mechanical forces resulting from contraction of the heart muscle itself and fluctuations in haemodynamic load and pressure. These forces are in flux on a beat-by-beat basis, resulting from changes in posture, physical activity or emotional state, and over longer timescales due to altered physiology (e.g. pregnancy) or as a consequence of ageing or disease (e.g. hypertension). It has been known for over a century of the heart's ability to sense differences in haemodynamic load and adjust contractile force accordingly (Frank, Z. biology, 1895, 32, 370-447; Anrep, J. Physiol., 1912, 45 (5), 307-317; Patterson and Starling, J. Physiol., 1914, 48 (5), 357-79; Starling, The law of the heart (Linacre Lecture, given at Cambridge, 1915), 1918). These adaptive behaviours are important for cardiovascular homeostasis, but the mechanism(s) underpinning them are incompletely understood. Here we present evidence that the mechanically-activated ion channel, Piezo, is an important component of the Drosophila heart's ability to adapt to mechanical force. We find Piezo is a sarcoplasmic reticulum (SR)-resident channel and is part of a mechanism that regulates Ca2+ handling in cardiomyocytes in response to mechanical stress. Our data support a simple model in which Drosophila Piezo transduces mechanical force such as stretch into a Ca2+ signal, originating from the SR, that modulates cardiomyocyte contraction. We show that Piezo mutant hearts fail to buffer mechanical stress, have altered Ca2+ handling, become prone to arrhythmias and undergo pathological remodelling.

Piezo acts as a molecular brake on wound closure to ensure effective inflammation and maintenance of epithelial integrity.

Wound healing entails a fine balance between re-epithelialization and inflammation1,2 so that the risk of infection is minimized, tissue architecture is restored without scarring, and the epithelium regains its ability to withstand mechanical forces. How the two events are orchestrated in vivo remains poorly understood, largely due to the experimental challenges of simultaneously addressing mechanical and molecular aspects of the damage response. Here, exploiting Drosophila's genetic tractability and live imaging potential, we uncover a dual role for Piezo-a mechanosensitive channel involved in calcium influx3-during re-epithelialization and inflammation following injury in vivo. We show that loss of Piezo leads to faster wound closure due to increased wound edge intercalation and exacerbated myosin cable heterogeneity. Moreover, we show that loss of Piezo leads to impaired inflammation due to lower epidermal calcium levels and, subsequently, insufficient damage-induced ROS production. Despite initially appearing beneficial, loss of Piezo is severely detrimental to the long-term effectiveness of repair. In fact, wounds inflicted on Piezo knockout embryos become a permanent point of weakness within the epithelium, leading to impaired barrier function and reduced ability of wounded embryos to survive. In summary, our study uncovers a role for Piezo in regulating epithelial cell dynamics and immune cell responsiveness during damage repair in vivo. We propose a model whereby Piezo acts as molecular brake during wound healing, slowing down closure to ensure activation of sustained inflammation and re-establishment of a fully functional epithelial barrier.

Validating the Predicted Effect of Astemizole and Ketoconazole Using a Drosophila Model of Parkinson's Disease.

Parkinson's disease is a growing threat to an ever-ageing population. Despite progress in our understanding of the molecular and cellular mechanisms underlying the disease, all therapeutics currently available only act to improve symptoms and do not stop the disease process. It is therefore imperative that more effective drug discovery methods and approaches are developed, validated, and used for the discovery of disease-modifying treatments for Parkinson's. Drug repurposing has been recognized as being equally as promising as de novo drug discovery in the field of neurodegeneration and Parkinson's disease specifically. In this work, we utilize a transgenic Drosophila model of Parkinson's disease, made by expressing human alpha-synuclein in the Drosophila brain, to validate two repurposed compounds: astemizole and ketoconazole. Both have been computationally predicted to have an ameliorative effect on Parkinson's disease, but neither had been tested using an in vivo model of the disease. After treating the flies in parallel, results showed that both drugs rescue the motor phenotype that is developed by the Drosophila model with age, but only ketoconazole treatment reversed the increased dopaminergic neuron death also observed in these models, which is a hallmark of Parkinson's disease. In addition to validating the predicted improvement in Parkinson's disease symptoms for both drugs and revealing the potential neuroprotective activity of ketoconazole, these results highlight the value of Drosophila models of Parkinson's disease as key tools in the context of in vivo drug discovery, drug repurposing, and prioritization of hits, especially when coupled with computational predictions.

Turning into frogs: Asymmetry in forelimb emergence and escape direction in metamorphosing anurans.

There is considerable debate about the pattern and origin of laterality in forelimb emergence and turning behaviour within amphibians, with the latter being poorly investigated in tadpoles around metamorphic climax. Using 6 species of metamorphosing anurans, we investigated the effect of asymmetrical spiracle location, and disturbance at the time of forelimb emergence, on the pattern of forelimb emergence. Turning behaviour was observed to assess whether motor lateralization occurred in non-neobatrachian anurans and was linked to patterns of forelimb emergence. Biases in forelimb emergence differed among species, supporting the hypothesis that asymmetrical spiracle position results in the same asymmetry in forelimb emergence. However, this pattern only occurred when individuals were undisturbed. Therefore, context at the time of the emergence of the forelimbs may be important, and might explain some discrepancies in the literature. Turning biases, unconnected to forelimb emergence, were found in Pipidae and Bombinatoridae, confirming the basal origin of lateralized behaviour among anurans. Turning direction in our metamorphs differed from the leftward bias commonly observed in tadpoles, but may be analogous to the prevalent right-"handedness" among adult anurans. Therefore, the transitions occurring during metamorphosis may affect lateralized behaviour and metamorphosis may be fruitful for understanding the development of lateralization.

Facial markings in the social cuckoo wasp Polistes sulcifer: No support for the visual deception and the assessment hypotheses.

Insect social parasites have to conquer a host colony by overcoming its defensive barriers. In addition to increased fighting abilities, many social parasites evolved sophisticated sensory deception mechanisms to elude host colonies defenses by exploiting host communication channels. Recently, it has been shown that the conspicuous facial markings of a paper wasp social parasite, Polistes sulcifer, decrease the aggressiveness of host foundresses. Two main hypotheses stand as explanations of this phenomenon: visual sensory deception (i.e. the black patterning reduces host aggression by exploiting the host visual communication system) and visual quality assessment (i.e. facial markings reduce aggressiveness as they signal the increased fighting ability of parasites). Through behavioral assays and morphological measurements we tested three predictions resulting from these hypotheses and found no support either for the visual sensory deception or for the quality assessment to explain the reduction in host aggressiveness towards the parasite. Our results suggest that other discrimination processes may explain the observed phenomenon.

Gain-of-function mutations in the ALS8 causative gene VAPB have detrimental effects on neurons and muscles.

Amyotrophic Lateral Sclerosis (ALS) is a motor neuron degenerative disease characterized by a progressive, and ultimately fatal, muscle paralysis. The human VAMP-Associated Protein B (hVAPB) is the causative gene of ALS type 8. Previous studies have shown that a loss-of-function mechanism is responsible for VAPB-induced ALS. Recently, a novel mutation in hVAPB (V234I) has been identified but its pathogenic potential has not been assessed. We found that neuronal expression of the V234I mutant allele in Drosophila (DVAP-V260I) induces defects in synaptic structure and microtubule architecture that are opposite to those associated with DVAP mutants and transgenic expression of other ALS-linked alleles. Expression of DVAP-V260I also induces aggregate formation, reduced viability, wing postural defects, abnormal locomotion behavior, nuclear abnormalities, neurodegeneration and upregulation of the heat-shock-mediated stress response. Similar, albeit milder, phenotypes are associated with the overexpression of the wild-type protein. These data show that overexpressing the wild-type DVAP is sufficient to induce the disease and that DVAP-V260I is a pathogenic allele with increased wild-type activity. We propose that a combination of gain- and loss-of-function mechanisms is responsible for VAPB-induced ALS.