Biology subjects

Olson, M. F.

Publications and source records attributed to Olson, M. F..

4 recordsLinked to original sources

bioRxiv2022

Actomyosin-mediated cellular tension promotes Yap nuclear translocation and myocardial proliferation through alpha5 integrin signaling

The cardiomyocyte phenotypic switch from a proliferative to terminally differentiated state results in the loss of regenerative potential of the mammalian heart shortly after birth. Yet, the molecular mechanisms that regulate this critical developmental process are incompletely understood. Nonmuscle myosin IIB (NM IIB)-mediated actomyosin contractility regulates cardiomyocyte cytokinesis in the embryonic heart, and NM IIB levels decline after birth suggesting a role for cellular tension in the regulation of cardiomyocyte cell cycle activity in the postnatal heart. The Rho kinase (ROCK) serine/threonine protein kinases that act downstream of the RhoA small GTP-binding protein regulate nonmuscle myosin contractile force generation. To investigate the role of actomyosin contractility in cardiomyocyte maturation and cell cycle arrest, we conditionally-activated ROCK2 kinase domain (ROCK2:ER) in the murine postnatal heart. Here we show that cardiac-specific activation of actomyosin contractility shifts the balance from cell-cell to cell-matrix adhesions. Specifically, 5/{beta}1 integrin and fibronectin matrix increase in response to actomyosin-mediated tension. Moreover, activation of ROCK2:ER promotes nuclear translocation of Yap, a mechanosensitive transcriptional co-activator, and enhances cardiomyocyte proliferation. Finally, we show that reduction of myocardial 5 integrin rescues the myocardial proliferation phenotype in ROCK2:ER hearts. These data demonstrate that cardiomyocytes respond to increase intracellular tension by altering their intercellular contacts in favor of cell-matrix interactions leading to Yap nuclear translocation, thus uncovering a novel function for nonmuscle myosin contractility in promoting cardiomyocyte cell cycle activity in the postnatal heart.

developmental biology↗

bioRxiv2022

Immunogenic cell death in mice expressing caspase-resistant ROCK1 is not replicated by ROCK inhibitors

The characteristic changes in morphology during apoptosis help facilitate "immunologically-silent" cell death by limiting the release of cellular contents and enabling efficient clearance of apoptotic cell bodies. Caspase-mediated cleavage of the ROCK1 protein kinase results in its constitutive activation, which drives the rapid and forceful contraction of apoptotic cells. We previously showed in Julian et al. [1] that when ROCK1 was mutated to render it caspase-resistant, there was greater liver damage and neutrophil recruitment after acute treatment with the hepatotoxin diethylnitrosamine (DEN). We now show that acute DEN-induced liver damage resulted in greater induction of pro-inflammatory cytokines/chemokines, indicative of immunogenic cell death (ICD), in mice expressing non-cleavable ROCK1 (ROCK1nc). Hepatocellular carcinoma (HCC) tumours in ROCK1nc mice had higher grade steatosis, and more neutrophils and CD8+ T cells relative to mice expressing wild-type ROCK1 (ROCK1wt), indicating that spontaneous tumour cell death also was more immunogenic. Since the induction of ICD has been proposed to be tumour-suppressive, the effects of two structurally distinct pharmacological ROCK inhibitors on HCC tumours was examined. Both fasudil and AT13148 significantly decreased tumour numbers and area, but neither treatment resulted in greater numbers of neutrophils or CD8+ T cells to be recruited. In the context of acute DEN-induced liver damage, AT13148 reduced circulating platelet and lymphocyte numbers, and inhibited the recruitment of dendritic, natural killer and CD8+ T cells to livers. These observations indicate that there is an important role for ROCK1 cleavage to limit immunogenic cell death which was not replicated by systemic administration of pharmacological ROCK inhibitors. As a result, adjuvant administration of ROCK inhibitors with cancer therapeutics would be unlikely to result in therapeutic benefit by inducing ICD to increase anti-tumour immune responses.

cancer biology↗

bioRxiv2021

MICAL1 activation by PAK1 mediates actin filament disassembly

The MICAL1 monooxygenase has emerged as an important regulator of filamentous actin (F-actin) structures that contribute to numerous processes including nervous system development, cell morphology, motility, viability and cytokinesis [1-4]. Activating MICAL1 mutations have been linked with autosomal-dominant lateral temporal epilepsy, a genetic syndrome characterized by focal seizures with auditory symptoms [5], emphasizing the need for tight control of MICAL1 activity. F-actin binding to MICAL1 stimulates catalytic activity, resulting in the oxidation of actin methionine residues that promote F-actin disassembly [6, 7]. Although MICAL1 has been shown to be regulated via interactions of the autoinhibitory carboxyl-terminal coiled-coil region [8] with RAB8, RAB10 and RAB35 GTPases [9-12], or Plexin transmembrane receptors [13, 14], a mechanistic link between the RHO GTPase signaling pathways that control actin cytoskeleton dynamics and the regulation of MICAL1 activity had not been established. Here we show that the CDC42 GTPase effector PAK1 serine/threonine kinase associates with and phosphorylates MICAL1 on serine 817 (Ser817) and 960 (Ser960) residues, leading to accelerated F-actin disassembly. Deletion analysis mapped PAK1 binding to the amino-terminal catalytic monooxygenase and calponin domains, distinct from the carboxyl-terminal proteinprotein interaction domain. Stimulation of cells with extracellular ligands including basic fibroblast growth factor (FGF2) led to significant PAK-dependent Ser960 phosphorylation, thus linking extracellular signals to MICAL1 phosphorylation. Moreover, mass spectrometry analysis revealed that co-expression of MICAL1 with CDC42 and active PAK1 resulted in hundreds of proteins increasing their association with MICAL1, including the previously described MICAL1-interacting protein RAB10 [15]. These results provide the first insight into a redox-mediated actin disassembly pathway linking extracellular signals to cytoskeleton regulation via a RHO GTPase family member, and reveal a novel means of communication between RHO and RAB GTPase signaling pathways.

cell biology↗

bioRxiv2020

Global patterns of aegyptism without arbovirus

The worlds most important mosquito vector of viruses, Aedes aegypti, is found around the world in tropical, subtropical and even some temperate locations. While climate change may limit populations of Ae. aegypti in some regions, increasing temperatures will likely expand its territory thus increasing risk of human exposure to arboviruses in places like Europe, Northern Australia and North America, among many others. Most studies of Ae. aegypti biology and virus transmission focus on locations with high endemicity or severe outbreaks of human amplified urban arboviruses, such as dengue, Zika, and chikungunya viruses, but rarely on areas at the margins of endemicity. Our objective in this study is to explore global patterns in the environmental suitability for Ae. aegypti and dengue virus to reveal deviations in the probability of the vector and human disease occurring. We developed a map showing one end of the gradient being higher suitability of Ae. aegypti with low suitability of dengue and the other end of the spectrum being equal and higher environmental suitability for both Ae. aegypti and dengue. The regions of the world with Ae. aegypti environmental suitability and no endemic dengue transmission exhibits a phenomenon we term aegyptism without arbovirus. We then tested what environmental and socioeconomic variables influence this deviation map revealing a significant association with population density, suggesting that locations with lower population density were more likely to have a higher probability of aegyptism without arbovirus. Characterizing regions of the world with established populations of Ae. aegypti but little to no autochthonous transmission of human-amplified arboviruses is an important step in understanding and achieving aegyptism without arbovirus.

ecology↗