Biology subjects

Pitenis, A. A.

Publications and source records attributed to Pitenis, A. A..

3 recordsLinked to original sources

bioRxiv2025

Optogenetic Control of the Integrated Stress Response Limits Glioblastoma Invasion

The integrated stress response (ISR) is a highly conserved cellular signaling network, allowing cells to adapt and respond to various stressors. In one of the toughest cancers to date, glioblastoma multiforme (GBM) with aggressive spread and high recurrence rates, the role of the ISR is yet to be well understood - whether activation may suppress or promote this disease - and drug-treatment of GBM has thus far shown inconclusive results. In this work we use an optogenetic tool, opto- PKR, to specifically trigger ISR-activation with light with high spatiotemporal control via the PKR-kinase, avoiding potential upstream damage or side effects from drugs. Using immunofluorescence and RNA-sequencing we show that targeted ISR-activation reaches levels where both adaptive (ATF4) and terminal response (CHOP) of the ISR are activated, which show downregulation of genes associated with extracellular environment and glial cell migration, further supported by ECM-stain and scratch assays. Further, we show inhibition of aggressive spread for ISR-activated GBM spheroids in collagen 3D culture. Photopatterning of ISR-activation in spheroids demonstrates a cell intrinsic effect at tissue scale, and recovery studies indicate a tunable, non-ablative intervention space. These findings suggest a route to containment and motivate ISR-activating small molecule screening in GBM models.

cancer biology↗

bioRxiv2025

Multiscale mechanics of granular biofilms

Biofilms produce and maintain extracellular polymeric substances (EPS) essential for their form and function. While biofilms are commonly lamellar and frequently targets of removal, granular biofilms are increasingly incorporated into water treatment strategies. In both cases, the EPS (mainly consisting of proteins, polysaccharides, and extracellular DNA) is largely responsible for their persistence. Unlike many granular biofilms, which are formed in engineered industrial bioreactors, the "pink berry" consortia is a naturally-occurring and robust granular biofilm of photosynthetic bacteria, found only in intertidal pools of salt marshes around Woods Hole, Massachusetts (USA). The pink berry biofilms unique ecological niche has sparked over three decades of study, yet their mechanical properties are completely unknown. Here, we characterized the structural and mechanical landscape of pink berry granules to determine the extent to which microscale heterogeneity influences macroscale material properties. We performed microindentation measurements on intact granules and nanoindentation measurements on thin sections. We report that intact pink berry granules exhibited low reduced elastic moduli (E*pink berry {approx} 0.5-10 kPa) and fast stress relaxation times ({tau}1/2 {approx} seconds), consistent with previous investigations of soft and viscoelastic biofilms. Nanomechanical measurements of thin pink berry sections revealed two mechanically-distinct domains: a very soft extracellular polymeric substance (EPS) matrix surrounding stiffer microcolonies of purple sulfur bacteria (PSB). Light sheet fluorescence microscopy revealed the spatial organization and distribution of cell-dense PSB microcolonies (34 vol.%) within EPS matrix (66 vol.%), suggesting the nanomechanical behavior of EPS dominates macroscale pink berry mechanics. Our multiscale experimental approach combining mechanics and imaging may be broadly applicable to investigations of complex soft materials, from synthetic hydrogel composites to biologically heterogeneous spheroids, organoids, and tissues.

biophysics↗

bioRxiv2024

Stress relaxation rates of myocardium from failing and non-failing hearts

The heart is a dynamic pump whose function is influenced by its mechanical properties. The viscoelastic properties of the heart, i.e. its ability to exhibit both elastic and viscous characteristics upon deformation, influence cardiac function. Viscoelastic properties change during heart failure (HF), but, direct measurements of failing and non-failing myocardial tissue stress relaxation under constant displacement are lacking. Further, how consequences of tissue remodeling, such as fibrosis and fat accumulation, alter the stress relaxation remains unknown. To address this gap, we conducted stress relaxation tests on porcine myocardial tissue to establish baseline properties of cardiac tissue. We found porcine myocardial tissue to be fast relaxing, characterized by stress relaxation tests on both a rheometer and microindenter. We then measured human left ventricle (LV) epicardium and endocardium human tissue from non-failing, ischemic HF, and non-ischemic HF patients by microindentation. We found that the ischemic HF had slower stress relaxation than non-failing endocardium; and that slower stress relaxing tissues were correlated with increased collagen deposition and increased -smooth muscle actin (-SMA) stress fibers, a marker of fibrosis and cardiac fibroblast activation, respectively. In the epicardium, we found that ischemic HF had faster stress relaxation than non-ischemic HF and non-failing; and that faster stress relaxation correlated with Oil Red O staining, a marker for adipose tissue. These data show that changes in stress relaxation vary across the different layers of the heart during ischemic vs. non-ischemic HF. These findings reveal how the viscoelasticity of the heart changes, which will lead to better modeling of cardiac mechanics for in vitro and in silico HF models.

bioengineering↗