Biology subjects

Steltzer, S. S.

Publications and source records attributed to Steltzer, S. S..

5 recordsLinked to original sources

bioRxiv2026

Hydrogel dimensionality directs mechanics-dependent nascent matrix deposition by tendon fibroblasts

Tendon fibroblasts continuously synthesize and remodel extracellular matrix (ECM) in response to their surrounding mechanical environment in vivo and in vitro, yet how dimensionality regulates the deposition of newly synthesized matrix remains poorly understood. Here, we investigated nascent matrix deposition by primary mouse tail tendon fibroblasts cultured on flat two-dimensional (2D) or encapsulated within three-dimensional (3D) norbornene-modified hyaluronic acid hydrogels with tunable mechanical properties. Newly synthesized matrix was visualized using metabolic labeling with azido-galactosamine (GalNAz), which labels nascent glycoproteins deposited during culture. In 2D, increasing hydrogel elastic modulus from 10 to 25 kPa enhanced nascent matrix deposition. This response was accompanied by increased cell spreading and YAP nuclear localization, indicating increased cellular mechanosensing. In contrast, tendon fibroblasts encapsulated within enzymatically degradable 3D hydrogels showed progressive matrix deposition over time but deposited less nascent matrix in stiffer (~50 kPa) hydrogels compared with softer 5 and 10 kPa hydrogels. YAP nuclear localization was increased in softer hydrogels compared with 50 kPa hydrogels. Bulk RNA sequencing showed increased expression of tendon matrisome-associated genes in softer 3D hydrogels, including increased tenascin C and collagen type I expression. These findings demonstrate that hydrogel dimensionality determines the relationship between matrix mechanics and nascent matrix deposition. This work establishes a framework for studying how engineered microenvironments regulate the matrix-producing behavior of tendon fibroblasts and provides insight into the design of biomaterials for investigating tendon biology and matrix remodeling.

bioengineering↗

bioRxiv2025

The developing tendon and enthesis are hypoxic and rely on hypoxia-inducible factor 1a (Hif1a) during postnatal development

The tendon-bone enthesis is a specialized fibrocartilaginous tissue crucial for muscle-to-bone force transmission, yet its postnatal development is not fully understood. Emerging evidence suggests hypoxia plays a pivotal role in enthesis maturation akin to its function in skeletal growth plates, with Hypoxia Inducible Factor 1 alpha (HIF-1) acting as a key regulator of cellular adaptation (e.g., cell survival, extracellular matrix (ECM) deposition). Here, we investigated the spatial and temporal dynamics of hypoxia in the murine Achilles tendon enthesis and elucidated the role of Hif1a in enthesis cell survival and ECM formation using Scleraxis-lineage conditional knockout (ScxCre; Hif1a cKO) mice. We found that while neonatal tendons rapidly resolve hypoxia after birth, the enthesis maintains a hypoxic niche through postnatal day 5, mirroring a gradient observed in growth plates. Disruption of HIF-1 in enthesis-resident cells resulted in pronounced deficits in grip strength, abnormal tendon-bone attachment morphology, disrupted calcaneal architecture, impaired mineralization, and significant ECM disorganization. Histological analyses revealed persistent cell death and loss of the characteristic fibrocartilaginous gradient in cKO entheses, including dysregulated collagen alignment. In vitro, HIF-1-deficient tendon fibroblasts exhibited blunted transcriptional responses to hypoxia, altered metabolic gene expression, and changes in ECM deposition. Collectively, our findings illuminate hypoxia as a sustained niche in the postnatal enthesis, with HIF-1 critically required for cell survival, ECM organization, and enthesis structural integrity. This work advances our understanding of enthesis biology and provides insights relevant to tendon-bone attachment disorders and regenerative strategies.

developmental biology↗

bioRxiv2025

Candida auris skin colonization is mediated by Als4112 and interactions with host extracellular matrix proteins

Candida auris is an often multidrug-resistant fungal pathogen notorious for persistent skin colonization and transmission in healthcare settings. However, the mechanisms driving its adherence to skin remain poorly understood. Here, we developed in vitro systems to allow for detailed analysis of early skin colonization events and identified critical host and pathogen mediators of attachment. Across multiple strains and clades of C. auris, we identified that Als4112, a conserved adhesin, is required for skin colonization via keratinocyte attachment and direct interactions with host extracellular matrix (ECM) proteins, especially basement membrane proteins such as laminin. In a murine epicutaneous infection and human skin explants, deletion of ALS4112 significantly reduced skin colonization, underscoring its essential role in establishing cutaneous persistence. Als4112 also contributes to systemic infection, highlighting the connection between adherence and pathogenicity in this organism. Finally, coating plastic and catheter surfaces with collagen I or III markedly inhibited C. auris attachment and biofilm formation, offering an approach to curb nosocomial transmission. Our study highlights the critical role of Als4112 in C. auris colonization and virulence in vivo, making it an attractive target for future vaccine development. This study also explores the potential of specific collagen coatings as a novel strategy to prevent C. auris adherence to abiotic surfaces, offering new therapeutic avenues to control the spread of C. auris in healthcare settings.

microbiology↗

bioRxiv2025

AMPK signaling is dysregulated in human tendinopathy and loss of AMPKα1 leads to cell, matrix and mechanical dysfunction in mouse Achilles tendon

Tendinopathy is a debilitating tendon disorder affecting millions of people, characterized by pain, swelling, and diminished biomechanical properties. While the precise mechanisms underlying tendon homeostasis remain unclear, metabolic regulation plays a critical role. In this study, we combine transcriptomic analysis of human tendinopathic samples with a conditional mouse model in which Prkaa1 (encoding AMPK1) is selectively deleted in tendon progenitors to elucidate the role of AMPK signaling in tendon homeostasis. RNA sequencing of diseased human tendons revealed downregulation of key metabolic genes, including several involved in the mitochondrial electron transport chain and AMPK signaling pathways, alongside an increase in markers associated with senescence and a secretory inflammatory profile. In parallel, mice with loss of Prkaa1 function exhibited normal postnatal development; however, by one month of age, tendons demonstrated widespread transcriptional alterations related to cell cycle regulation and ECM organization. By three months, AMPK1-deficient tendons showed significant reductions in mechanical strength and increased expression of senescence markers p21 and p16, progressing to prominent ectopic calcification with age. In vitro studies further confirmed that tendon fibroblasts lacking AMPK1 have altered ECM substrate adhesion profiles. Importantly, voluntary exercise partially rescued these deficits by enhancing ECM organization and reducing senescence marker expression. Collectively, our findings demonstrate that AMPK1 is critical for maintaining energy balance, regulating ECM remodeling, and preventing premature cellular senescence in tendon. These insights highlight AMPK signaling as a promising therapeutic target and underscore the beneficial role of exercise in mitigating tendinopathic changes.

pathology↗

bioRxiv2019

Human iPSC modeling elucidates mutation-specific responses to gene therapy in a genotypically diverse dominant maculopathy

Dominantly inherited disorders are not typically considered therapeutic candidates for gene augmentation. Here, we utilized patient-specific induced pluripotent stem cell-derived retinal pigment epithelium (iPSC-RPE) to test the potential of gene augmentation to treat Best disease, a dominant macular dystrophy caused by over 200 missense mutations in BEST1. Gene augmentation in iPSC-RPE fully restored BEST1 calcium-activated chloride channel activity and improved rhodopsin degradation in iPSC-RPE models of recessive bestrophinopathy and dominant Best disease caused by two different ion binding domain mutations. A dominant Best disease iPSC-RPE model that did not respond to gene augmentation showed normalization of BEST1 channel activity following CRISPR-Cas9 editing of the mutant allele. We then tested gene editing in all three dominant Best disease iPSC-RPE models, which produced premature stop codons exclusively within the mutant BEST1 alleles. Single-cell profiling demonstrated no adverse perturbation of RPE transcriptional programs in any model, although off-target analysis detected a silent genomic alteration in one model. These results suggest that gene augmentation is a viable first-line approach for some dominant Best disease patients and that non-responders are candidates for alternate approaches such as genome editing. However, testing genome editing strategies for on-target efficiency and off-target events using patient-matched iPSC-RPE model systems is warranted. In summary, personalized iPSC-RPE models can be used to select among a growing list of gene therapy options to maximize safety and efficacy while minimizing time and cost. Similar scenarios likely exist for other genotypically diverse channelopathies, expanding the therapeutic landscape for affected patients. SignificanceDominantly inherited disorders pose distinct challenges for gene therapies, particularly in the face of extreme mutational diversity. We tested whether a broad gene replacement strategy could reverse the cellular phenotype of Best disease, a dominant blinding condition that targets retinal pigment epithelium (RPE). Using RPE generated from patient-specific induced pluripotent stem cells (iPSCs), we show that gene replacement functionally overcomes some, but not all, of the tested mutations. In comparison, all dominant Best disease models tested were phenotypically corrected after mutation-specific genome editing, although one off-target genomic alteration was discovered. Our results support a two-tiered approach to gene therapy for Best disease, guided by safety and efficacy testing in iPSC-RPE models to maximize personal and public health value.

genetics↗