Biology subjects

Martinson, A. M.

Publications and source records attributed to Martinson, A. M..

4 recordsLinked to original sources

bioRxiv2019

High-Resolution 3D Fluorescent Imaging of Intact Tissues

Histological analysis of fluorescently labeled tissues has been a critical tool to understand molecular organization in situ. However, assessing molecular structures within large cells and in the context of human organ anatomy has been challenging because it requires penetration of staining reagents and light deep into opaque tissues, while also conforming to the spatial constraints of high-resolution objective lenses. This methodology article describes optimized sample preparation for sub-micron resolution 3D imaging in human and rodent tissues, yielding imaging depth (>100 {micro}m) and resolution (<0.012 {micro}m3 voxel size) that has previously been limited to whole-mount in vitro organoid systems, embryos, and small model organisms. Confocal images of adult human and rodent organs, including heart, kidney, and liver, were generated for several chemical and antibody stains in cleared tissue sections >100 {micro}m thick. This method can be readily adopted by any lab performing routine histology and takes 3 days from the start of tissue preparation to 3D images.

cell biology↗

bioRxiv2019

Engrafted Human Induced Pluripotent Stem Cell-Derived Cardiomyocytes Undergo Clonal Expansion In Vivo

Preclinical studies have suggested that transplanted human pluripotent stem cell-derived cardiomyocyte (hPSC-CM) grafts expand due to proliferation. This knowledge came from cell cycle activity measurements that cannot discriminate between cytokinesis or DNA synthesis associated with hypertrophy. To refine our understanding of hPSC-CM cell therapy, we genetically engineered a cardiomyocyte-specific fluorescent barcoding system into an hPSC line. Since cellular progeny have the same color as parental hPSC-CMs, we could identify subsets of engrafted hPSC-CMs that clonally expanded, with the remainder being non-proliferative and hypertrophic.

cell biology↗

bioRxiv2019

Delta-1 functionalized hydrogel promotes hESC-cardiomyocyte graft proliferation and maintains heart function post-injury

Current cell transplantation techniques are hindered by small graft size, requiring high cell doses to achieve therapeutic cardiac remuscularization. Enhancing the proliferation of transplanted human stem cell-derived cardiomyocytes (hESC-CMs) could address this, allowing an otherwise subtherapeutic cell dose to prevent disease progression after myocardial infarction. Here, we designed a hydrogel that activates Notch signaling through 3D presentation of the Notch ligand Delta-1 to use as an injectate for transplanting hESC-CMs into the infarcted rat myocardium. After four weeks, hESC-CM proliferation increased 2-fold and resulted in a 3-fold increase in graft size with the Delta-1 hydrogel compared to controls. To stringently test the effect of Notch-mediated graft expansion on long-term heart function, a normally subtherapeutic dose of hESC-CMs was implanted into the infarcted myocardium and cardiac function was evaluated by echocardiography. Transplantation of the Delta-1 hydrogel + hESC-CMs augmented heart function and was significantly higher at three months compared to controls. Graft size and hESC-CM proliferation were also increased at three months post-implantation. Collectively, these results demonstrate the therapeutic approach of a Delta-1 functionalized hydrogel to reduce the cell dose required to achieve functional benefit after myocardial infarction by enhancing hESC-CM graft size and proliferation.

bioengineering↗

bioRxiv2018

Evidence for minimal cardiogenic potential of Sca-1 positive cells in the adult mouse heart

BackgroundDespite modern pharmacotherapy, heart failure remains a major medical burden. The heart has a limited regenerative capacity, and bolstering regeneration might represent new therapeutic approaches for heart failure patients. Various progenitor cells in the heart have been proposed to have cardiomyogenic properties, but this evidence is based mostly on cell culture and transplantation studies. One population of interest is characterized by the expression of Stem Cell Antigen-1 (Sca-1). Here we tested the hypothesis that Sca-1+ cells are endogenous progenitors for cardiomyocytes in the adult heart.\n\nMethodsWe evaluated the innate cardiogenic potential of Sca-1+ cells in vivo by generating a novel mouse model to genetically lineage-trace the fate of Sca-1 expressing cells. This was accomplished by introducing a tamoxifen-inducible Cre-recombinase into the Sca-1 locus (Sca-1mCm/+). Crossing this mouse line to a Cre-dependent tdTomato reporter line allowed for genetic lineage-tracing of endogenous Sca-1+ cells (Sca-1mCmR26tdTomato). The frequency of Sca-1+ cardiomyocytes was quantified from dispersed cell preparations and confirmed by in situ histology.\n\nResultsWe validated the genetic lineage tracing mouse model in bone marrow and heart. Unlike previous publications suggesting significant cardiogenic potential, we found that less than 0.02% of cardiomyocytes per year were derived from Sca-1+ cells in the adult heart under homeostatic conditions. At six months after myocardial infarction, we found less than 0.01% of cardiomyocytes were derived from Sca-1+ cells.\n\nConclusionOur results show that Sca-1+ cells in the adult heart have minimal cardiogenic potential under homeostatic conditions or in response to myocardial infarction.

cell biology↗