Experimental Control of Macrophage Pro-Inflammatory Dynamics Using Predictive Models

Temporal dynamics of immune-stromal cell interactions in fracture healing

Bone fracture repair is a complex, multi-step process that involves communication between immune and stromal cells to coordinate the repair and regeneration of damaged tissue. In the US, 10% of all bone fractures do not heal properly without intervention, resulting in non-union. Complications from non-union fractures are physically and financially debilitating. We now appreciate the important role that immune cells play in tissue repair, and the necessity of the inflammatory response in initiating healing after skeletal trauma. The temporal dynamics of immune and stromal cell populations have been well characterized across the stages of fracture healing. Recent studies have begun to untangle the intricate mechanisms driving the immune response during normal or atypical, delayed healing. Various in vivo models of fracture healing, including genetic knockouts, as well as in vitro models of the fracture callus, have been implemented to enable experimental manipulation of the heterogeneous cellular environment. The goals of this review are to (1): summarize our current understanding of immune cell involvement in fracture healing (2); describe state-of-the art approaches to study inflammatory cells in fracture healing, including computational and in vitro models; and (3) identify gaps in our knowledge concerning immune-stromal crosstalk during bone healing.

Sodium alginate microencapsulation of human mesenchymal stromal cells modulates paracrine signaling response and enhances efficacy for treatment of established osteoarthritis

Mesenchymal stromal cells (MSCs) have shown promise as osteoarthritis (OA) treatments; however, effective translation has been limited by high variability and heterogeneity of MSCs, suboptimal delivery strategies, and poor understanding of critical quality and potency attributes. Furthermore, most pre-clinical studies of MSC therapeutics for OA have focused on delaying OA development and not on treating established OA, which brings added clinical relevance. Thus, the objective of the current study was to assess the effects of sodium alginate microencapsulation on human MSC (hMSC) secretion of immunomodulatory cytokines in an OA microenvironment and therapeutic efficacy in treating established OA. A Medial Meniscal Transection (MMT) pre-clinical model of OA was implemented. Three weeks post-surgery, after OA was established, intra-articular injections of encapsulated hMSCs or nonencapsulated hMSCs were administered. Six weeks post-surgery, microstructural changes in the knee joint were quantified using microCT. Encapsulated hMSCs reduced articular cartilage degeneration and subchondral bone remodeling. A multiplexed immunoassay panel was used to profile the in vitro secretome of hMSCs in response to IL-1β. Nonencapsulated hMSCs showed an indiscriminate increase in all cytokines in response to IL-1β while encapsulated hMSCs showed a targeted secretory response with increased expression of pro-inflammatory (IL-1β, IL-6, IL-7, IL-8), anti-inflammatory (IL-1RA), and chemotactic (G-CSF, MDC, IP10) cytokines. These data show that sodium alginate microencapsulation can modulate hMSC paracrine signaling and enhance the therapeutic efficacy of the hMSCs in treating established OA. This cytokine profile provides a foundation for the identification of key factors affecting the overall potency of hMSC therapeutics for OA. STATEMENT OF SIGNIFICANCE: While there has been considerable interest in material based MSC encapsulation for treatment of OA, there are critical gaps in our translational understanding of these biomaterial-based technologies for OA. More specifically, previous studies have several important limitations: (1) they have been largely focused on preventing OA development, which limits their translational utility and (2) little prior work has been done to delineate potential routes/mechanisms by which material encapsulation alters MSC therapeutic action. In our manuscript, we aimed to fill these gaps in knowledge by testing the hypotheses that: (1) hMSC encapsulation can attenuate established disease progression, which is a more clinically relevant scenario and (2) hMSC encapsulation significantly changes the secreted paracrine factors from hMSCs.