Interleukin-1β in tendon injury enhances reparative gene and protein expression in mesenchymal stem cells

Abstract

Tendon injury in the horse carries a high morbidity and monetary burden. Despite appropriate therapy, reinjury is estimated to occur in 50–65% of cases. Although intralesional mesenchymal stem cell (MSC) therapy has improved tissue architecture and reinjury rates, the mechanisms by which they promote repair are still being investigated. Additionally, reevaluating our application of MSCs in tendon injury is necessary given recent evidence that suggests MSCs exposed to inflammation (deemed MSC licensing) have an enhanced reparative effect. However, applying MSC therapy in this context is limited by the inadequate quantification of the temporal cytokine profile in tendon injury, which hinders our ability to administer MSCs into an environment that could potentiate their effect. Therefore, the objectives of this study were to define the temporal cytokine microenvironment in a surgically induced model of equine tendon injury using ultrafiltration probes and subsequently evaluate changes in MSC gene and protein expression following in vitro inflammatory licensing with cytokines of similar concentration as identified in vivo. In our in vivo surgically induced tendon injury model, IL-1β and IL-6 were the predominant pro-inflammatory cytokines present in tendon ultrafiltrate where a discrete peak in cytokine concentration occurred within 48 h following injury. Thereafter, MSCs were licensed in vitro with IL-1β and IL-6 at a concentration identified from the in vivo study; however, only IL-1β induced upregulation of multiple genes beneficial to tendon healing as identified by RNA-sequencing. Specifically, vascular development, ECM synthesis and remodeling, chemokine and growth factor function alteration, and immunomodulation and tissue reparative genes were significantly upregulated. A significant increase in the protein expression of IL-6, VEGF, and PGE2 was confirmed in IL-1β-licensed MSCs compared to naïve MSCs. This study improves our knowledge of the temporal tendon cytokine microenvironment following injury, which could be beneficial for the development and determining optimal timing of administration of regenerative therapies. Furthermore, these data support the need to further study the benefit of MSCs administered within the inflamed tendon microenvironment or exogenously licensed with IL-1β in vitro prior to treatment as licensed MSCs could enhance their therapeutic benefit in the healing tendon.

Preclinical tendon and ligament models: Beyond the 3Rs (replacement, reduction, and refinement) to 5W1H (why, who, what, where, when, how)

“…As an alternative, several groups developed a surgically induced model that appears to mimic clinical injury 184,185 . When an equine surgical SDFT model is implemented (Figure 14), standardized lesions can be obtained, horses can be maintained comfortably following lesion induction, and postoperative rehabilitation procedures can be initiated 184–186 . Additionally, the large size of the tendon and induced core lesion present an opportunity for testing of implantable medical devices or administered therapeutics as well as providing ample diseased and healthy tissue for a variety of outcome measures without the need for sample pooling 186 .…”

“…Surgical injury to the extra‐synovial portion of the equine SDFT can be created as previously reported 185,186 . This technique requires the expertise, personnel, and equipment of a veterinary surgeon at a veterinary hospital, therefore it is referenced and not further described.…”

“…184,185 When an equine surgical SDFT model is implemented (Figure 14), standardized lesions can be obtained, horses can be maintained comfortably following lesion induction, and postoperative rehabilitation procedures can be initiated. [184][185][186] Additionally, the large size of the tendon and induced core lesion present an opportunity for testing of implantable medical devices or administered therapeutics as well as providing ample diseased and healthy tissue for a variety of outcome measures without the need for sample pooling. 186 These advantages suggest that surgically induced injury rather than the collagenase model might be more appropriate for study of tendon injury utilizing an equine model (Table 2).…”

“…[184][185][186] Additionally, the large size of the tendon and induced core lesion present an opportunity for testing of implantable medical devices or administered therapeutics as well as providing ample diseased and healthy tissue for a variety of outcome measures without the need for sample pooling. 186 These advantages suggest that surgically induced injury rather than the collagenase model might be more appropriate for study of tendon injury utilizing an equine model (Table 2).…”

“…Surgical injury to the extra-synovial portion of the equine SDFT can be created as previously reported. 185,186 This technique requires the expertise, personnel, and equipment of a veterinary surgeon at a veterinary hospital, therefore it is referenced and not further described. This model however is ideal for collaborations between veterinary clinician scientists and biomedical engineers, medical clinician scientists, or other researchers who study tendon injury as it provides a viable means to study tendon injury and novel therapies through a preclinical large animal model that recapitulates a specific aspect of human tendon injury.…”