Role of Primary Afferents in Arthritis Induced Spinal Microglial Reactivity.

Increased afferent input resulting from painful injury augments the activity of central nociceptive circuits via both neuron-neuron and neuron-glia interactions. Microglia, resident immune cells of the central nervous system (CNS), play a crucial role in the pathogenesis of chronic pain. This study provides a framework for understanding how peripheral joint injury signals the CNS to engage spinal microglial responses. During the first week of monosodium iodoacetate (MIA)-induced knee joint injury in male rats, inflammatory and neuropathic pain were characterized by increased firing of peripheral joint afferents. This increased peripheral afferent activity was accompanied by increased Iba1 immunoreactivity within the spinal dorsal horn indicating microglial activation. Pharmacological silencing of C and A afferents with co-injections of QX-314 and bupivacaine, capsaicin, or flagellin prevented the development of mechanical allodynia and spinal microglial activity after MIA injection. Elevated levels of ATP in the cerebrospinal fluid (CSF) and increased expression of the ATP transporter vesicular nucleotide transporter (VNUT) in the ipsilateral spinal dorsal horn were also observed after MIA injections. Selective silencing of primary joint afferents subsequently inhibited ATP release into the CSF. Furthermore, increased spinal microglial reactivity, and alleviation of MIA-induced arthralgia with co-administration of QX-314 with bupivacaine were recapitulated in female rats. Our results demonstrate that early peripheral joint injury activates joint nociceptors, which triggers a central spinal microglial response. Elevation of ATP in the CSF, and spinal expression of VNUT suggest ATP signaling may modulate communication between sensory neurons and spinal microglia at 2 weeks of joint degeneration.

Collagen I scaffolds cross-linked with beta-glycerol phosphate induce osteogenic differentiation of embryonic stem cells in vitro and regulate their tumorigenic potential in vivo.

Embryonic stem cells (ESCs) have the potential to differentiate into all tissues of the adult organism. This, along with the ability for unlimited self-renewal, positions these cells for regenerative medicine approaches based on tissue engineering strategies. With the objective of developing a treatment regime for skeletal injuries and diseases, this study presents a novel protocol that effectively induces ESC differentiation into osteogenic and chondrogenic lineages while concurrently eliminating observed tumorigenicity during the period of observation after transplantation in vivo. Exposure to a collagen I matrix polymerized with beta-glycerol phosphate (BGP) induced the osteogenic differentiation of the ESCs with an efficiency of >80% without purification and/or lineage-specific cell selection. Furthermore, when the collagen I matrix was supplemented with chondroitin sulfate, chondrogenesis was promoted instead of osteogenesis. Interestingly, without purification of the differentiated cells from the collagen I matrix, these constructs did not lead to the formation of teratomas or tumors when implanted subcutaneously in a severe combined immunodeficiency (SCID). Furthermore, if undifferentiated ESCs were mixed with collagen I and then injected immediately (i.e., without previous in vitro differentiation), again, no teratomas or tumors were observed, whereas undifferentiated ESCs without collagen scaffolds all produced teratomas in this bioassay system. These results suggest that collagen I scaffolds not only induce osteogenic differentiation of ESCs, but also prevent ESCs from producing unwanted tumors when injected in vivo.