Mesenchymal stromal cells (MSCs) have great potential to maintain glucose homeostasis and metabolic balance. Here, we demonstrate that in mice continuously fed with high-fat diet (HFD) that developed non-insulindependent diabetes, two episodes of systemic MSC transplantations effectively improve glucose tolerance and blood glucose homeostasis and reduce body weight through targeting pancreas and insulin-sensitive tissues and organs via site-specific mechanisms. MSCs support pancreatic islet growth by direct differentiation into insulin-producing cells and by mitigating the cytotoxicity of interleukin 1 (IL-1) and tumor necrosis factor-a (TNF-a) in the pancreas. Localization of MSCs in the liver and skeletal muscles in diabetic animals is also enhanced and therefore improves glucose tolerance, although long-term engraftment is not observed. MSCs prevent HFD-induced fatty liver development and restore glycogen storage in hepatocytes. Increased expression of IL-1 receptor antagonist and Glut4 in skeletal muscles after MSC transplantation results in better blood glucose homeostasis. Intriguingly, systemic MSC transplantation does not alter adipocyte number, but it decreases HFD-induced cell infiltration in adipose tissues and reduces serum levels of adipokines, including leptin and TNF-a. Taken together, systemic MSC transplantation ameliorates HFD-induced obesity and restores metabolic balance through multisystemic regulations that are niche dependent. Such findings have supported systemic transplantation of MSCs to correct metabolic imbalance.Impairment of glucose tolerance and insulin resistance initiates type 2 diabetes; however, exhaustion of the insulin supply due to b-cell apoptosis is the ultimate pathomechanism of both type 1 and 2 diabetes (1,2). The liver, adipose tissues, skeletal muscles, and vascular tissues are insulin-sensitive tissues responsible for blood glucose homeostasis (1,3). Inflammation adversely affects insulin sensitivity and worsens diabetic retinopathies, neuropathies, and vasculopathies (4-6). Proinflammatory cytokines produced by macrophages, such as tumor necrosis factor-a (TNF-a) and interleukin 1 (IL-1), create a vicious cycle of reduced insulin sensitivity (3,(7)(8)(9).To the present, more than 300 clinical trials of mesenchymal stem/stromal cell (MSC) transplantations have been conducted worldwide with a wide clinical application targeting more than 50 indications (www.clinicaltrials.gov). Systemic transplantation is the most favorable route for MSC delivery from a safety and systemic regulation point of view, and 56% of MSC clinical trials are allogenic transplantation (10). It is well accepted that the majority of MSCs are initially distributed in vital organs (11-16) and are also frequently found in tissues of mesenchymal origin (11,12) when systemically administered. Nevertheless, the long-term engraftment of MSCs is minimal, and the engraftment rate is not correlated with therapeutic response in human studies (17). The acutely diseased and damaged tissues show increased loca...