No abstract

In patients with T1D experiencing problematic hypoglycemia, intrahepatic islet transplantation can lead to long-term improvement of glucose counterregulation and hypoglycemia symptom recognition, physiological effects that likely contribute to glycemic stability after transplant.

ABSTRACTrange of clinical pathologies, including idiopathic recurrent miscarriage, 19 fetal hemoglobin expression in Brazilian patients with sickle cell anemia, 20 and pre-eclampsia. 21Splenic macrophages are central to whole body iron recycling and return the iron from cleared RBC to the BM for use in erythropoiesis. 16,22 Hmox1 plays a critical role in this iron recycling and regulates the ability of splenic macrophages to tolerate the toxic heme released during RBC clearance. 16Hmox1 is expressed in splenic macrophages and is up-regulated in other cell types in response to heme and oxidative stress. 23 Splenic macrophages are significantly decreased in mice lacking Hmox1, 16 resulting in iron redistribution from the spleen and hepatic Küpffer cells to hepatocytes and proximal tubular cells of the kidney. 16 Inappropriate handling of heme and tissue deposition of iron in Hmox1 -/-mice and HMOX1-deficient patients results in increased oxidative stress and vascular cell injury. 16,17 Hematopoiesis and stress erythropoiesis in Hmox1 +/-mice has been investigated recently. BM cells from Hmox1 +/-mice are less capable of reconstituting lethally irradiated recipient animals. 24 Moreover, mice with a hematopoietic system reconstituted from Hmox1 +/-donor animals demonstrate decreased stress erythropoiesis in response to anemia. 25 Here, we investigated erythropoiesis in the complete absence of the Hmox1 gene and protein expression and without exerting exogenous stress in young, 8-to 14-week old mice. We found significant alterations in the BM, circulating and splenic erythroid populations in Hmox1 -/-mice. In the BM, the number of EBI macrophages was decreased and the expression of adhesion molecules was altered in erythroblast and macrophage populations, manifested as the inability of Hmox1-deficient BM to form EBI. Hmox1-deficient RBC also showed profound changes in redox biology and lifespan. Splenic erythropoiesis was almost completely absent and splenic macrophages involved in RBC removal were severely depleted. Our findings document defects in RBC production and lifespan resulting from the loss of this crucial heme-catabolizing enzyme. MethodsFull details of the materials and methods are provided in the Online Supplementary Methods. Mice Hmox1+/-breeders on a BALB/c background were obtained from Dr MP Soares (Instituto de Gulbenkian de Ciencia, Portugal) from a colony generated originally by Dr SF Yet. 26 Flow cytometry and cytological analysisBlood, BM, spleen and liver single cell suspensions were treated with FcR-block (MACS Miltenyi Biotech) then with appropriate antibodies for 1 h at 4°C. A list of antibodies is presented in Online Supplementary Table S1. The presence of a nucleus or surface membrane phosphatidylserine was assessed as described in the Online Supplementary Methods. Resuspended samples were analyzed using FACSCalibur (Becton Dickinson) and FlowJo software. Iron staining was performed on methanol-fixed cytospun BM samples using the Iron Stain Kit (Sigma Aldrich) according to the manufacturer...

Objective: Hmox1 (heme oxygenase-1) is a stress-induced enzyme that catalyzes the degradation of heme to carbon monoxide, iron, and biliverdin. Induction of Hmox1 and its products protect against cardiovascular disease, including ischemic injury. Hmox1 is also a downstream target of the transcription factor HIF-1α (hypoxia-inducible factor-1α), a key regulator of the body’s response to hypoxia. However, the mechanisms by which Hmox1 confers protection against ischemia-mediated injury remain to be fully understood. Approach and Results: Hmox1 deficient ( Hmox1 –/– ) mice had impaired blood flow recovery with severe tissue necrosis and autoamputation following unilateral hindlimb ischemia. Autoamputation preceded the return of blood flow, and bone marrow transfer from littermate wild-type mice failed to prevent tissue injury and autoamputation. In wild-type mice, ischemia-induced expression of Hmox1 in skeletal muscle occurred before stabilization of HIF-1α. Moreover, HIF-1α stabilization and glucose utilization were impaired in Hmox1 –/– mice compared with wild-type mice. Experiments exposing dermal fibroblasts to hypoxia (1% O 2 ) recapitulated these key findings. Metabolomics analyses indicated a failure of Hmox1 –/– mice to adapt cellular energy reprogramming in response to ischemia. Prolyl-4-hydroxylase inhibition stabilized HIF-1α in Hmox1 –/– fibroblasts and ischemic skeletal muscle, decreased tissue necrosis and autoamputation, and restored cellular metabolism to that of wild-type mice. Mechanistic studies showed that carbon monoxide stabilized HIF-1α in Hmox1 –/– fibroblasts in response to hypoxia. Conclusions: Our findings suggest that Hmox1 acts both downstream and upstream of HIF-1α, and that stabilization of HIF-1α contributes to Hmox1’s protection against ischemic injury independent of neovascularization.

Islet transplantation results in improved insulin sensitivity mediated by effects at both the liver and skeletal muscle. Modern dosing of glucocorticoid-free immunosuppression with low-dose tacrolimus and sirolimus does not induce insulin resistance in this population.