IntroductionAdipose-derived mesenchymal stem cells (Ad-MSCs) are highly multipotent cells with a high potential for differentiation into multiple cell types (Vieira et al., 2010;Park et al., 2012;Mellor et al., 2015). Ad-MSCs produce various growth factors that contribute to injury healing and tissue regeneration (Salgado et al., 2010). The antiinflammatory, immunomodulatory, and antioxidant properties of mesenchymal stem cells (MSCs) make them desirable candidates for cell-based therapies (Soleymaninejadian et al., 2012).The usefulness of MSCs has been selectively enhanced by either manipulating the culture media composition (Langenbach and Handschel, 2013) or by gene transduction (Liu et al., 2015). Pretreatment with proinflammatory cytokines, such as tumor necrosis factor-α (TNF-α), interferon-γ (INF-γ), and interleukin-6 (IL-6), enhances the immunosuppressive capacity of MSCs by upregulating the expression of indoleamine-2,3-dioxygenase (IDO), which inhibits the proliferation of lymphocytes (Hoogduijn et al., 2010). Gelatin sponges incorporating high amounts of β-tricalcium phosphate (β TCP) have been used to stimulate rat bone marrow MSC proliferation and osteogenic differentiation by stimulating higher alkaline phosphatase (AP) activity and osteocalcin expression (Takahashi et al., 2005). Similarly, a scaffold prepared by mixing chitosan with gelatin, β TCP, and hydroxyapatite (HA) has also been used to induce MSC adhesion, differentiation, and proliferation (Zhao et al., 2006).MSCs cultured in a hyperoxic environment have enhanced viability and paracrine therapeutic capabilities (Song et al., 2010), as well as increased expression of the naturally occurring antioxidant stanniocalcin-1 (SC-1), which prevents oxygen-induced bronchopulmonary dysplasia in rats (Waszak et al., 2012). HO-1, a potent antioxidant enzyme, can be induced in undifferentiated MSCs treated with hemin, which renders the MSCs more resistant to oxidative injury (Barbagallo et al., 2008). Osteogenic growth peptide (OGP) induces HO-1 expression in human bone marrow MSCs, which induces osteogenic differentiation as evidenced by elevated levels of bone morphogenic protein-2 (BMP-2) and osteonectin (Vanella et al., 2010(Vanella et al., , 2013. We have previously reported that gelatin-induced osteogenic cell sheets had active cell proliferation with abundant extracellular matrix and upregulation of osteogenic markers (Kim et al., 2016). In the present study, we evaluated the effects of gelatin on