Dissecting the Therapeutic Mechanisms of Sphingosine-1-Phosphate Receptor Agonism during Ischaemia and Reperfusion

BEST PRACTICES OF HEART TRANSPLANTATION IN MICE

Heart transplantation in mice has served as a reliable in vivo model in transplant research worldwide for more than half a century. It is not only useful for addressing cardiac graft-specific questions but also provides mechanistic insights and therapeutic strategies that have broad impact across all solid organ transplants. Compared to other mouse models of solid organ transplantation, such as kidney, lung, or small intestine transplants, the surgical techniques to perform mouse heart transplantation (mHT) are relatively easy to master, and the graft heartbeat offers a simple means to evaluate transplant viability. However, as with other in vivo mouse models, mHT has distinct strengths and limitations. Multiple factors can influence the accuracy and reproducibility of the results, including microsurgical techniques and microsurgeons' skills, post-op monitoring methodologies, mouse strain combinations, sex/age. As innovative biotechnologies continue to emerge, the future holds many opportunities for preclinical research utilizing the mHT model. It is therefore imperative to provide the field with optimized mHT protocols and maintain standard reporting requirements. This minireview provides a concise summary and recommendations for standardized practices to ensure the accuracy, reproducibility, and translational value of findings generated from mHT model.

Accelerating Oral Wound Healing Using Bilayer Biomaterial Delivery of FTY720 Immunotherapy

Orofacial clefts are the most common congenital craniofacial anomaly. Adverse healing following cleft palate repair can lead to oronasal fistula (ONF), a persistent connection between the oral and nasal cavities. Although human allograft tissues are currently the gold standard for ONF repair, these methods carry risks of infection and rejection, often requiring surgical revision. Immunoregenerative therapies present a novel alternative approach to harness the body's immune response and enhance the wound healing environment. An FDA-approved immunomodulatory drug, FTY720, is repurposed to reduce lymphocyte egress and induce immune cell fate switching toward pro-regenerative phenotypes. In this study, a bilayer biomaterial system is engineered using Tegaderm to secure and control the delivery of FTY720-nanofiber scaffolds (FTY720-NF). The release kinetics of the bilayer FTY720-NF is optimized to maintain drug release for up to 7 days, ensuring safe transdermal absorption and tissue biodistribution. The comprehensive immunophenotyping results demonstrate a regenerative state transition in hybrid immune cells recruited to the wound site. Further, histological evaluations reveal a significant ONF closure in mice by day 7 following bilayer FTY720-NF implantation. These findings demonstrate the utility of immunomodulatory strategies for oral wound healing, better positing the field to develop more efficacious treatment options in pediatric patients.

Sphingosine-1-Phosphate Receptor 4 links neutrophils and early local inflammation to lymphocyte recruitment into the draining lymph node to facilitate robust germinal center formation

The successful development of germinal centers (GC) relies heavily on innate mechanisms to amplify the initial inflammatory cascade. In addition to their role in antigen presentation, innate cells are essential for the redirection of circulating lymphocytes toward the draining lymph node (dLN) to maximize antigen surveillance. Sphingosine-1-Phosphate (S1P) and its receptors (S1PR1-5) affect various aspects of immunity; however, the role of S1PR4 in regulating an immune response is not well understood. Here we use a footpad model of localized TH1 inflammation to carefully monitor changes in leukocyte populations within the blood, the immunized tissue, and the dLN. Within hours of immunization, neutrophils failed to adequately mobilize and infiltrate into the footpad tissue of S1PR4-/- mice, thereby diminishing the local vascular changes thought to be necessary for redirecting circulating cells toward the inflamed region. Neutrophil depletion with anti-Ly6G antibodies significantly reduced early tissue edema as well as the redirection and initial accumulation of naïve lymphocytes in dLN of WT mice, while the effects were less prominent or absent in S1PR4-/- dLN. Adoptive transfer experiments further demonstrated that the lymphocyte homing deficiencies in vivo were not intrinsic to the donor S1PR4-/- lymphocytes, but were instead attributed to differences within the S1PR4-deficient host. Reduced cell recruitment in S1PR4-/- mice would seed the dLN with fewer antigen-respondent lymphocytes and indeed, dLN hypertrophy at the peak of the immune response was severely diminished, with attenuated GC and activation pathways in these mice. Histological examination of the S1PR4-/- dLN also revealed an underdeveloped vascular network with reduced expression of the leukocyte tethering ligand, PNAd, within high endothelial venule regions, suggesting inadequate growth of the dLN meant to support a robust GC response. Thus, our study reveals that S1PR4 may link early immune modulation by neutrophils to the initial recruitment of circulating lymphocytes and downstream expansion and maturation of the dLN, thereby contributing to optimal GC development during an adaptive response.

1-Phosphate receptor agonists: A promising therapeutic avenue for ischemia-reperfusion injury management

Ischemia-reperfusion injury (IRI) - a complex pathological condition occurring when blood supply is abruptly restored to ischemic tissues, leading to further tissue damage - poses a significant clinical challenge. Sphingosine-1-phosphate receptors (S1PRs), a specialized set of G-protein-coupled receptors comprising five subtypes (S1PR1 to S1PR5), are prominently present in various cell membranes, including those of lymphocytes, cardiac myocytes, and endothelial cells. Increasing evidence highlights the potential of targeting S1PRs for IRI therapeutic intervention. Notably, preconditioning and postconditioning strategies involving S1PR agonists like FTY720 have demonstrated efficacy in mitigating IRI. As the synthesis of a diverse array of S1PR agonists continues, with FTY720 being a prime example, the body of experimental evidence advocating for their role in IRI treatment is expanding. Despite this progress, comprehensive reviews delineating the therapeutic landscape of S1PR agonists in IRI remain limited. This review aspires to meticulously elucidate the protective roles and mechanisms of S1PR agonists in preventing and managing IRI affecting various organs, including the heart, kidney, liver, lungs, intestines, and brain, to foster novel pharmacological approaches in clinical settings.

Harnessing Bilayer Biomaterial Delivery of FTY720 as an Immunotherapy to Accelerate Oral Wound Healing

Orofacial clefts are the most common craniofacial congenital anomaly. Following cleft palate repair, up to 60% of surgeries have wound healing complications leading to oronasal fistula (ONF), a persistent connection between the roof of the mouth and the nasal cavity. The current gold standard methods for ONF repair use human allograft tissues; however, these procedures have risks of graft infection and/or rejection, requiring surgical revisions. Immunoregenerative therapies present a novel alternative approach to harness the body's immune response and enhance the wound healing environment. We utilized a repurposed FDA-approved immunomodulatory drug, FTY720, to reduce the egress of lymphocytes and induce immune cell fate switching toward pro-regenerative phenotypes. Here, we engineered a bilayer biomaterial system using Tegaderm™, a liquid-impermeable wound dressing, to secure and control the delivery of FTY720- nanofiber scaffolds (FTY720-NF). We optimized release kinetics of the bilayer FTY720-NF to sustain drug release for up to 7d with safe, efficacious transdermal absorption and tissue biodistribution. Through comprehensive immunophenotyping, our results illustrate a pseudotime pro-regenerative state transition in recruited hybrid immune cells to the wound site. Additional histological assessments established a significant difference in full thickness ONF closure in mice on Day 7 following treatment with bilayer FTY720-NF, compared to controls. These findings demonstrate the utility of immunomodulatory strategies for oral wound healing, better positing the field to develop more efficacious treatment options for pediatric patients.

One Sentence Summary

Local delivery of bilayer FTY720-nanofiber scaffolds in an ONF mouse model promotes complete wound closure through modulation of pro-regenerative immune and stromal cells.

The Role of Sphingolipids and Sphingosine-1-phosphate-Sphingosine-1-phosphate-receptor Signaling in Psoriasis

Psoriasis is a long-lasting skin condition characterized by redness and thick silver scales on the skin's surface. It involves various skin cells, including keratinocytes, dendritic cells, T lymphocytes, and neutrophils. The treatments for psoriasis range from topical to systemic therapies, but they only alleviate the symptoms and do not provide a fundamental cure. Moreover, systemic treatments have the disadvantage of suppressing the entire body's immune system. Therefore, a new treatment strategy with minimal impact on the immune system is required. Recent studies have shown that sphingolipid metabolites, particularly ceramide and sphingosine-1-phosphate (S1P), play a significant role in psoriasis. Specific S1P-S1P-receptor (S1PR) signaling pathways have been identified as crucial to psoriasis inflammation. Based on these findings, S1PR modulators have been investigated and have been found to improve psoriasis inflammation. This review will discuss the metabolic pathways of sphingolipids, the individual functions of these metabolites, and their potential as a new therapeutic approach to psoriasis.