Biology subjects

Annamalai, R. T.

Publications and source records attributed to Annamalai, R. T..

4 recordsLinked to original sources

bioRxiv2023

Sex-Specific Systemic Inflammatory Responses in Mice Infected with a SARS-CoV-2-like Virus and Femur Fracture

Patients with femur fractures who are concurrently infected with COVID-19 face a threefold increase in mortality, likely due to a compounded inflammatory response. Furthermore, sex-specific differences in immune responses to COVID-19 have been documented, implicating gender as a potential modulator of disease severity in these comorbid conditions. Understanding the inflammatory interplay underlying this association is critical for the development of effective, targeted therapies to mitigate mortality. In this study, we investigated the systemic, sex-specific inflammatory response in mice that sustain a fracture while infected with a murine coronavirus (MHV), which belongs to the same genus as SARS-CoV-2. Our findings reveal that the combined inflammatory incidents of MHV infection and fracture disrupt the systemic immune response in both female and male mice, leading to immune dysregulation characterized by altered cell recruitment and disruption of the normal inflammatory cascade. Notably, the study identifies sex-specific differences in immune response, with female subjects exhibiting significantly elevated levels of inflammatory cytokines, including IL-18 and TNF, while males exhibit a diminished response. These sexually dimorphic differences are also reflected in the systemic immune cell populations, suggesting that the quantity of immune factors released may contribute to the observed discrepancies. Notably, these differences were minimal or moderate in animals that either got an MHV infection or fracture alone. Our findings indicate that the overproduction of proinflammatory cytokines, such as IFN{gamma}, IL-18, and TNF--reminiscent of cytokine storm syndrome--drives immune dysregulation, exacerbating outcomes in patients with these comorbidities. The observed sex-specific responses may be influenced by factors such as sex hormones, including estrogen, highlighting the importance of considering gender in therapeutic approaches. These insights provide a foundation for the development of tailored interventions to improve outcomes for COVID-19 patients with musculoskeletal trauma, including fractures.

immunology↗

bioRxiv2023

A Murine Delayed-Healing Model Associates Immune Response with Functional Bone Regeneration after Trauma

Delayed and non-healing fractures, affecting 5-10% of cases, are associated with prolonged disability and diminished quality of life. Although acute inflammation is required to initiate repair, persistent mechanical instability can sustain maladaptive immune and fibrotic responses that impede regeneration. Existing animal models do not adequately recapitulate mechanical instability, the principal driver of hypertrophic nonunion in clinical settings, thereby limiting translational relevance. In this study, we developed a murine model of delayed fracture healing using tunable intramedullary fixation to impose controlled interfragmentary strain. High-strain conditions (low-stiffness nail, 15-30% strain) produced enlarged calluses characterized by delayed ossification, increased fibrotic tissue (2.9-fold, p = 0.0099), and reduced biomechanical integrity (1.6-fold decrease in stiffness, p = 0.024) relative to low-strain controls (high-stiffness nail, <5% strain). Spatial transcriptomic analysis identified persistent fibrotic niches in high-strain calluses enriched with fibroblast-associated genes (e.g., Pdgfrb, Lgals3) and dysregulated macrophage-fibroblast signaling (Spp1, Mmp9). Systemically, high-strain fractures were associated with distinct immune signatures in which CD206 macrophages and CD25 regulatory T cells predicted healing outcomes (R = 0.72, p = 0.004), suggesting early immune polarization as a determinant of repair trajectory. Elevated CD8 T cell responses were also observed, consistent with a sustained inflammatory state associated with impaired healing. These findings identify mechanical instability as a driver of pathological immune-stromal interactions and establish a preclinical platform for investigating mechanobiology-informed therapeutic strategies. This work supports a conceptual framework in which hypertrophic nonunion is understood as a disorder arising from dysregulated interactions between mechanical cues and immune responses. TeaserMechanical strain hijacks immune signaling to induce fibrosis and block bone regeneration in unstable fractures.

bioengineering↗

bioRxiv2022

Licensing Microgels Prolong the Immunomodulatory Phenotype of Mesenchymal Stromal Cells

Mesenchymal stromal cells (MSC) are sensors of inflammation, and they exert immunomodulatory properties through the secretion of cytokines and exosomes and direct cell-cell interactions. MSC are routinely used in clinical trials and effectively resolve inflammatory conditions. Nevertheless, inconsistent clinical outcomes necessitate the need for more robust therapeutic phenotypes. The immunomodulatory properties of MSC can be enhanced and protracted by priming (aka licensing) them with IFN{gamma} and TNF. Yet these enhanced properties rapidly diminish, and prolonged stimulation could tolerize their response. Hence a balanced approach is needed to enhance the therapeutic potential of the MSC for consistent clinical performance. Here, we investigated the concentration-dependent effects of IFN{gamma} and TNF and developed gelatin-based microgels to sustain a licensed MSC phenotype. We show that IFN{gamma} treatment is more beneficial than TNF in promoting an immunomodulatory MSC phenotype. We also show that the microgels possess integrin-binding sites to support MSC attachment and a net positive charge to sequester the licensing cytokines electrostatically. Microgels are enzymatically degradable, and the rate is dependent on the enzyme concentration and matrix density. Our studies show that one milligram of microgels by dry mass can sequester up to 641 {+/-} 81 ng of IFN{gamma}. Upon enzymatic degradation, microgels exhibited a sustained release of IFN{gamma} that linearly correlated with their degradation rate. The MSC cultured on the IFN{gamma} sequestered microgels displayed efficient licensing potential comparable to or exceeding the effects of bolus IFN{gamma} treatment. When cultured with proinflammatory M1-like macrophages, the MSC-seeded on licensing microgel showed an enhanced immunomodulatory potential compared to untreated MSC and MSC treated with bolus IFN{gamma} treatment. Specifically, the MSC seeded on licensing microgels significantly upregulated Arg1, Mrc1, and Igf1, and downregulated Tnfa in M1-like macrophages compared to other treatment conditions. These licensing microgels are a potent immunomodulatory approach that shows substantial promise in elevating the efficacy of current MSC therapies and may find utility in treating chronic inflammatory conditions.

bioengineering↗

bioRxiv2018

Modular microtissues for the regeneration of functional bone in large defects

Repair of complex fractures with bone loss requires a potent, space-filling intervention to promote regeneration of bone. We present a minimally-invasive strategy combining mesenchymal stromal cells (MSC) with a chitosan-collagen matrix to form modular microtissues designed for delivery through a needle to conformally fill cavital defects. Implantation of microtissues into a calvarial defect in the mouse showed that osteogenically pre-differentiated MSC resulted in complete bridging of the cavity, while undifferentiated MSC produced mineralized tissue only in apposition to native bone. Decreasing the implant volume reduced bone regeneration, while increasing the MSC concentration also attenuated bone formation, suggesting that the cell-matrix ratio is important in achieving a robust response. Conformal filling of the defect with microtissues in a carrier gel resulted in complete healing. Taken together, these results show that modular microtissues can be used to augment the differentiated function of MSC and provide an extracellular environment that potentiates bone repair.

bioengineering↗