Biology subjects

Obaid, G.

Publications and source records attributed to Obaid, G..

4 recordsLinked to original sources

bioRxiv2026

Whole-organ surface mapping using multiview projection reconstruction

While light-sheet microscopy is emerging as a robust method for volumetric imaging with improved axial resolution, its capability regarding two-dimensional, surface-level mapping is often hindered by limitations in data redundancy and reconstruction efficiency stemming from volumetric registration methods. We demonstrate that a multiview imaging approach in an axially-swept, dithered light-sheet microscope paired with computational image reconstruction of view projections is able to address these trade-offs to enable large-scale mapping of surface structural features, leveraging the advantages of multiview light-sheet in scalable field of view, working distance, and near isotropic resolution across the entire imaging depth. To aid in the acquisition and analysis of two-dimensional surface structures, we present a tailored surface mapping workflow and a Fiji plugin for computational reconstruction, promoting robust and comprehensive visualization of surface features of uncleared volumetric samples. Our strategy, termed projection reconstruction for imaging surface morphology (PRISM), integrates axially swept dithered light-sheet microscopy and post-processing software for multiview imaging. The imaging hardware enables near-isotropic resolution across its entire field of view, while the software implementation leverages rigid and affine transformations to align two-dimensional projections of multiview samples. It is designed to work with the BigStitcher pipeline, leveraging its robust algorithm to provide support for two-dimensional image alignment and stitching. We demonstrate the capability of PRISM in studies of lymphatic network mapping in the epicardial layer of intact mouse hearts, as well as surface profiles of FaDu spheroids labeled with antibody-nanodiamond conjugates. This method allows us to quantify cardiac lymphatic branch numbers, diameters, and lengths of a Prox1-tdTomato mouse cardiac model, as well as cluster number and diameters of epidermal growth factor receptor within a FaDu spheroid labeled with a nanodiamond-antibody conjugate, with a significant reduction of post-processing data size. PRISM leverages multiview image projections to promote studies of cardiac lymphatics in mouse models and surface receptor distributions within spheroid models, enabling efficient surface mapping of large, intact, and uncleared biological samples across a variety of scales.

bioengineering↗

bioRxiv2026

Dissecting the Dynamic Evolution of Tensional Homeostasis in Fibroblasts using an Integrated Biomechanical Bioreactor Platform

Mechanical homeostasis indicates the remarkable ability displayed by cells in tissues to maintain their mechanical properties near a stable homeostatic set-point. Experimental investigations and theoretical studies indicate that mechanical stress represents a key homeostatic target that stromal cells, such as fibroblasts, seek to maintain by tuning the intracellular structure and by remodeling the extracellular matrix. Much of what is known about mechanical homeostasis of tissues under tension, or tensional homeostasis, is based on experiments on tissue equivalents, that is fibroblast-populated collagen gels. However, existing platforms used to investigate tensional homeostasis cannot infer mechanical stress dynamically. Here we developed an integrated biomechanical bioreactor combining force sensing with confocal and multiphoton microscopy to dissect the mechanobiological mechanisms of tensional homeostasis. We used our platform to test the hypothesis that fibroblasts maintain a constant state of stress across varying collagen concentrations. Contrary to this assumption, synchronized force and imaging measurements revealed that stress is not constant but rather elevated at low collagen concentrations, where fibroblast contraction drives earlier collagen alignment and greater tissue compaction. Conversely, force generation and -SMA expression increase with increasing collagen concentration, accompanied by modest transcriptional changes. However, at the highest collagen concentration, this homeostatic balance is disrupted, with lower force generation and -SMA expression, as gene expression shifts toward VEGFC-mediated autocrine survival signaling. These findings demonstrate that tensional homeostasis emerges from a dynamic balance between cellular contractility and extracellular matrix densification rather than stress maintenance while revealing that excessive matrix density disrupts this balance by triggering a pro-survival response.

bioengineering↗

bioRxiv2024

Photo-induced changes in tissue stiffness alter epithelial budding morphogenesis in the embryonic lung

Extracellular matrix (ECM) stiffness has been shown to influence the differentiation of progenitor cells in culture, but a lack of tools to perturb the mechanical properties within intact embryonic organs has made it difficult to determine how changes in tissue stiffness influence organ patterning and morphogenesis. Photocrosslinking of the ECM has been successfully used to stiffen soft tissues, such as the cornea and skin, which are optically accessible, but this technique has not yet been applied to developing embryos. Here, we use photocrosslinking with Rose Bengal (RB) to locally and ectopically stiffen the pulmonary mesenchyme of explanted embryonic lungs cultured ex vivo. This change in mechanical properties was sufficient to suppress FGF-10-mediated budding morphogenesis along the embryonic airway, without negatively impacting patterns of cell proliferation or apoptosis. A computational model of airway branching was used to determine that FGF-10-induced buds form via a growth-induced buckling mechanism and that increased mesenchymal stiffness is sufficient to inhibit epithelial buckling. Taken together, our data demonstrate that photocrosslinking can be used to create regional differences in mechanical properties within intact embryonic organs and that these differences influence epithelial morphogenesis and patterning. Further, this photocrosslinking assay can be readily adapted to other developing tissues and model systems.

bioengineering↗

bioRxiv2021

Photoimmunotherapy retains its anti-tumor efficacy with increasing stromal content in heterotypic pancreatic cancer spheroids

Pancreatic ductal adenocarcinoma (PDAC) is an aggressive disease characterized by increased levels of desmoplasia that contributes to reduced drug delivery and poor treatment outcomes. In PDAC, the stromal content can account for up to 90% of the total tumor volume. The complex interplay between stromal components, including pancreatic cancer associated fibroblasts (PCAFs), and PDAC cells in the tumor microenvironment (TME) have a significant impact on prognoses and thus needs to be recapitulated in vitro when evaluating various treatment strategies. This study is a systematic evaluation of photodynamic therapy (PDT) in 3D heterotypic coculture models of PDAC with varying ratios of patient derived PCAFs that simulate heterogenous PDAC tumors with increasing stromal content. The efficacy of antibody-targeted PDT (photoimmunotherapy; PIT) using cetuximab photoimmunoconjugates (PICs) of benzoporphyrin derivative (BPD) is contrasted with that of liposomal BPD (Visudyne(R)), which is currently in PDT clinical trials for PDAC. We demonstrate that both Visudyne(R)-PDT and PIT were effective in heterotypic PDAC 3D spheroids with a low stromal content. However, as the stromal content increases above 50% in the 3D spheroids, the efficacy of Visudyne(R)-PDT is reduced by up to 10-fold, while PIT retains its efficacy. PIT was found to be 10-fold, 19-fold and 14-fold more phototoxic in spheroids with 50%, 75% and 90% PCAFs, respectively, as compared to Visudyne(R)-PDT. This marked difference in efficacy is attributed to the ability of PICs to penetrate and distribute within spheroids with a higher stromal content, whereas Visudyne(R) is restricted to the spheroid periphery. This study thus demonstrates how the stromal content in PDAC spheroids directly impacts their responsiveness to PDT and proposes PIT to be a highly suited treatment option for desmoplastic tumors with particularly high degrees of stromal content.

cancer biology↗