Biology subjects

Connizzo, B. K.

Publications and source records attributed to Connizzo, B. K..

6 recordsLinked to original sources

bioRxiv2025

Inflammatory Crosstalk Between Rotator Cuff Tissues is Altered with Age and Sex

Musculoskeletal disorders, particularly those affecting the shoulder, are a significant health concern, especially in aging populations. Nevertheless, the initiating factors of joint degeneration remain poorly understood. Research has primarily focused on age-related changes in individual musculoskeletal tissues, with limited investigation into the complex interactions between tissues. Recent studies on interorgan communication between musculoskeletal tissues and other organs have gained attention, but local interactions within the shoulder remain underexplored. This study aims to investigate age- and sex-related differences in bone-tendon-muscle (BTM) crosstalk, hypothesizing that these interactions vary by age and sex, with older and female tissues exhibiting a reduced secretory phenotype. Using novel in vitro monoculture and co- cultures of explanted whole tissues, we assessed inflammatory responses across bone, tendon, and muscle from young and aged male and female C57BL/6J mice. Our results demonstrate significant age- and sex-dependent differences in cytokine secretion, with aged males and females showing altered inflammatory profiles. We observed a general increase in pro-inflammatory cytokine secretion in monocultures, with aging amplifying this response. Tissue co-cultures revealed that crosstalk between bone and tendon was primarily mediated through secreted factors, while muscle-tendon communication required physical proximity or contact, suggesting a distinct mode of interaction between these tissues. Sex differences were evident in both the individual tissue responses and in the patterns of inter-tissue communication. Importantly, our findings suggest that tendon plays a crucial role in mediating inter-tissue communication, with aging disrupting this crosstalk. However, these sex differences diminished with aging, indicating that the age-related decline in tissue-specific signaling may override sex-based distinctions.

bioengineering↗

bioRxiv2025

Intrinsic Repair Capacity of Resident Tendon Cells is Dependent on Hole Size in an Ex Vivo Model of Laser-Induced Microdamage

While it is generally accepted that tendon healing following widespread extracellular matrix trauma is limited, tenocytes are thought to have the capacity to repair small amounts of microdamage generated through activities of daily living. Despite this, few studies have directly studied the mechanisms governing this process. To address this, we developed a tunable in vitro model of extracellular matrix microdamage in live tendon explants that enables us to track both clearance of denatured collagen microdamage and closure of a micro-sized defect in the tendon matrix. The purpose of this study was to controllably induce varying levels of localized microdamage to the tendon explants and identify (1) if thresholds for healing exist and (2) whether repair mechanisms are dependent on initial damage size. We found that within three weeks, all tendon explants were able to clear damaged matrix to some extent regardless of the damage size. Interestingly, larger 5 mJ and 10 mJ injuries resulted in a more robust rate of damaged matrix clearance in the later weeks, while smaller injuries exhibited a more consistent rate that led to full clearance in two explants. Greater than 50% clearance of denatured collagen microdamage was typically associated with an accompanying closure of the ECM defect, suggesting a strong relationship between clearance and closure. Overall, our work demonstrates the power of our laser-induced microdamage model, which enables the direct visualization of microdamage responses. This model will be a powerful asset for investigating mechanisms of damage accumulation and/or healing, as well as identifying local tendon-specific factors that can be leveraged for therapeutics.

bioengineering↗

bioRxiv2025

Estrogen and progesterone exhibit distinct yet coordinated roles in the regulation of tendon extracellular matrix remodeling

Remodeling of the extracellular matrix (ECM) is required for the proper healing, strengthening, and maintenance of tendon tissue. There are well documented sex differences in tendon injury rates and healing outcomes, often attributed to either innate differences in tissue structure and resident cell signaling or the influence of sex hormones. However, these factors are rarely decoupled. Estrogen (17{beta}-estradiol) and progesterone (P4) receptors are expressed in both male and female tendons and thus could participate in the remodeling process, but studies are extremely limited. Therefore, the objective of this work was to address whether biological sex differences are present in tendon remodeling and to determine the individual and combined roles of estrogen and progesterone in the remodeling process. We utilized an explant model of the flexor digitorum longus tendon harvested from young adult male and female mice to examine cell-mediated remodeling without disruption to the native environment. We found sex differences in tendon remodeling in the absence of hormonal stimulation, revealing how biological sex alone influences tendon health. We also demonstrate that the response to exogenous hormone delivery is sex-dependent, and that progesterone and estrogen serve complimentary yet independent roles. Overall, this work presents the first examination of sex-dependent matrix turnover in response to hormones and underscores the critical need for additional research in this area.

bioengineering↗

bioRxiv2024

Coordination of Glucose and Glutamine Metabolism in Tendon is Lost in Aging

Tendinopathy is an age-associated degenerative disease characterized by a loss in extracellular matrix (ECM). Since glucose and glutamine metabolism is critical to amino acid synthesis and known to be altered in aging, we sought to investigate if age-related changes in metabolism are linked to changes in ECM remodeling. We exposed young and aged tendon explants to various concentrations of glucose and glutamine to observe changes in metabolic processing (enzyme levels, gene expression, etc.) and matrix biosynthesis. Interestingly, we found that glutamine processing is affected by glucose levels, but this effect was lost with aging. ECM synthesis was altered in a protein-dependent manner by increased glucose and glutamine levels in young tendons. However, these changes were not conserved in aged tendons. Overall, our work suggests that glucose and glutamine metabolism is important for ECM homeostasis, and age-related changes in nutrient metabolism could be a key driver of tendon degeneration.

bioengineering↗

bioRxiv2024

Aged Tendons Exhibit Altered Mechanisms of Strain-Dependent Extracellular Matrix Remodeling

Aging is a primary risk factor for degenerative tendon injuries, yet the etiology and progression of this degeneration is poorly understood. While aged tendons have innate cellular differences that support a reduced ability to maintain mechanical tissue homeostasis, the response of aged tendons to altered levels of mechanical loading has not yet been studied. To address this question, we subjected young and aged murine flexor tendon explants to various levels of in vitro tensile strain. We first compared the effect of static and cyclic strain on matrix remodeling in young tendons, finding that cyclic strain is optimal for studying remodeling in vitro. We then investigated the remodeling response of young and aged tendon explants after 7 days of varied mechanical stimulus (stress-deprivation, 1%, 3%, 5%, or 7% cyclic strain) via assessment of tissue composition, biosynthetic capacity, and degradation profiles. We hypothesized that aged tendons would show muted adaptive responses to changes in tensile strain and exhibit a shifted mechanical setpoint, at which the remodeling balance is optimal. Interestingly, we found 1% cyclic strain best maintains native physiology while promoting ECM turnover for both age groups. However, aged tendons display fewer strain-dependent changes, suggesting a reduced ability to adapt to altered levels of mechanical loading. This work has significant impact in understanding the regulation of tissue homeostasis in aged tendons, which can inform clinical rehabilitation strategies for treating elderly patients.

bioengineering↗

bioRxiv2023

Cellular Senescence Impairs Tendon Extracellular Matrix Remodeling in Response to Mechanical Unloading

Musculoskeletal injuries, including tendinopathies, present a significant clinical burden for aging populations. While the biological drivers of age-related declines in tendon function are poorly understood, it is well accepted that dysregulation of extracellular matrix (ECM) remodeling plays a role in chronic tendon degeneration. Senescent cells, which have been associated with multiple degenerative pathologies in musculoskeletal tissues, secrete a highly pro-inflammatory senescence-associated secretory phenotype (SASP) that has potential to promote ECM breakdown. However, the role of senescent cells in the dysregulation of tendon ECM homeostasis is largely unknown. To assess this directly, we developed an in vitro model of induced cellular senescence in murine tendon explants. This novel technique enables us to study the isolated interactions of senescent cells and their native ECM without interference from age-related systemic changes. We document multiple biomarkers of cellular senescence in induced tendon explants including cell cycle arrest, apoptosis resistance, and SASP production. We then utilize this in vitro senescence model to compare the ECM remodeling response of young, naturally aged, and senescent tendons to an altered mechanical stimulus. We found that both senescence and aging independently led to alterations in ECM-related gene expression, reductions in protein synthesis, and tissue compositional changes. Furthermore, MMP activity was sustained, thus shifting the remodeling balance of aged and senescent tissues towards degradation over production. Together, this demonstrates that cellular senescence plays a role in the altered mechano-response of aged tendons and likely contributes to poor clinical outcomes in aging populations.

bioengineering↗