Closed-loop cervical epidural stimulation partially restores ipsilesional diaphragm EMG after acute C2 hemisection.

Cervical spinal cord injury creates lasting respiratory deficits which can require mechanical ventilation long-term. We have shown that closed-loop epidural stimulation (CL-ES) elicits respiratory plasticity in the form of increased phrenic network excitability (Malone et. al., E Neuro, Vol 9, 0426-21.2021, 2022); however, the ability of this treatment to create functional benefits for breathing function per se after injury has not been demonstrated. Here, we demonstrate in C2 hemisected anesthetized rats, a 20-minute bout of CL-ES administered at current amplitudes below the motor threshold restores paralyzed hemidiaphragm activity in-phase with breathing while potentiating contralesional activity. While this acute bout of stimulation did not elicit the increased network excitability seen in our chronic model, a subset of stimulated animals continued spontaneous ipsilesional diaphragm activity for several seconds after stopping stimulation. These results support the use of CL-ES as a therapeutic to rescue breathing after high cervical spinal cord injury, with the potential to lead to lasting recovery and device independence.

Erythroferrone contributes to iron mobilization for embryo erythropoiesis in iron-deficient mouse pregnancies.

Erythroferrone (ERFE) is an erythroblast-secreted regulator of iron metabolism. The production of ERFE increases during stress erythropoiesis, leading to decreased hepcidin expression and mobilization of iron. Pregnancy requires a substantial increase in iron availability to sustain maternal erythropoietic expansion and fetal development and is commonly affected by iron deficiency. To define the role of ERFE during iron-replete or iron-deficient pregnancy, we utilized mouse models expressing a range of ERFE levels: transgenic (TG) mice overexpressing ERFE, wild-type (WT), and ERFE knockout (KO) mice. We altered maternal iron status using diets with low or standard iron content and performed the analysis at E18.5. Iron deficiency increased maternal ERFE in WT pregnancy. Comparing different maternal genotypes, ERFE TG dams had lower hepcidin relative to their liver iron load but similar hematological parameters to WT dams on either diet. In ERFE KO dams, most hematologic and iron parameters were comparable to WT, but mean corpuscular volume (MCV) was decreased under both iron conditions. Similar to dams, TG embryos had lower hepcidin on both diets, but their hematologic parameters did not differ from those of WT embryos. ERFE KO embryos had lower MCV than WT embryos on both diets. The effect was exacerbated under iron-deficient conditions where ERFE KO embryos had higher hepcidin, lower Hb and Hct, and lower brain iron concentration compared to WT embryos, indicative of iron restriction. Thus, under iron-deficient conditions, maternal and embryo ERFE facilitate iron mobilization for embryonic erythropoiesis.

Erythroid overproduction of erythroferrone causes iron overload and developmental abnormalities in mice.

The hormone erythroferrone (ERFE) is produced by erythroid cells in response to hemorrhage, hypoxia, or other erythropoietic stimuli, and it suppresses the hepatic production of the iron-regulatory hormone hepcidin, thereby mobilizing iron for erythropoiesis. Suppression of hepcidin by ERFE is believed to be mediated by interference with paracrine bone morphogenetic protein (BMP) signaling that regulates hepcidin transcription in hepatocytes. In anemias with ineffective erythropoiesis, ERFE is pathologically overproduced, but its contribution to the clinical manifestations of these anemias is not well understood. We generated 3 lines of transgenic mice with graded erythroid overexpression of ERFE and found that they developed dose-dependent iron overload, impaired hepatic BMP signaling, and relative hepcidin deficiency. These findings add to the evidence that ERFE is a mediator of iron overload in conditions in which ERFE is overproduced, including anemias with ineffective erythropoiesis. At the highest levels of ERFE overexpression, the mice manifested decreased perinatal survival, impaired growth, small hypofunctional kidneys, decreased gonadal fat depots, and neurobehavioral abnormalities, all consistent with impaired organ-specific BMP signaling during development. Neutralizing excessive ERFE in congenital anemias with ineffective erythropoiesis may not only prevent iron overload but may have additional benefits for growth and development.

Erythroferrone is not required for the glucoregulatory and hematologic effects of chronic erythropoietin treatment in mice.

Erythropoietin (EPO) acts on erythroid progenitor cells to promote their survival and differentiation to mature erythrocytes. Along with this canonical role, EPO is also reported to modulate energy metabolism, resulting in improved glucose tolerance and insulin sensitivity. EPO also stimulates the production of the hormone erythroferrone (ERFE) which acts to suppress hepcidin production, thus increasing dietary iron absorption and mobilizing stored iron for use in erythropoiesis. ERFE (initially termed myonectin) was also reported have an effect on systemic lipid metabolism by promoting the clearance of nonesterifed fatty acids (NEFA) from circulation. As increased levels of circulating NEFA blunt insulin sensitivity and impair glucose tolerance, ERFE-induced clearance of NEFA after EPO administration would have a beneficial effect on glucose metabolism. The aim of this study was to determine if the known metabolic effect of EPO treatment on glucose homeostasis is mediated by ERFE, produced in response to EPO. Mice lacking Erfe did not differ from wild-type mice in blood lipid parameters, blood glucose, and glucose or insulin tolerance at baseline or after chronic EPO treatment. Additionally, hepcidin suppression and the response of erythrocyte parameters to chronic EPO treatment were unaffected by the absence of Erfe. These findings suggest that the known beneficial effects of EPO on glucose metabolism are not attributable to an accompanying increase in ERFE production, and that Erfe is dispensable for normal glucose homeostasis. Furthermore, our data indicate that ERFE-independent mechanisms can suppress hepcidin in response to chronically elevated EPO levels.

Erythroferrone: An Erythroid Regulator of Hepcidin and Iron Metabolism.

Iron homeostasis ensures adequate iron for biological processes while preventing excessive iron accumulation, which can lead to tissue injury. In mammalian systems, iron availability is controlled by the interaction of the iron-regulatory hormone hepcidin with ferroportin, a molecule that functions both as the hepcidin receptor as well as the sole known cellular exporter of iron. By reducing iron export through ferroportin to blood plasma, hepcidin inhibits the mobilization of iron from stores and the absorption of dietary iron. Among the many processes requiring iron, erythropoiesis is the most iron-intensive, consuming most iron circulating in blood plasma. Under conditions of enhanced erythropoiesis, more iron is required to provide developing erythroblasts with adequate iron for heme and hemoglobin synthesis. Here the hormone erythroferrone, produced by erythroblasts, acts on hepatocytes to suppress hepcidin production, and thereby increase dietary iron absorption and mobilization from stores. This review focuses on the discovery of erythroferrone and recent advances in understanding the role of this hormone in the regulation of iron homeostasis during states of increased erythropoietic demand. Gaps in our understanding of the role of erythroferrone are highlighted for future study.

Iron homeostasis: An anthropocentric perspective.

The regulation of iron metabolism in biological systems centers on providing adequate iron for cellular function while limiting iron toxicity. Because mammals cannot excrete iron, mechanisms have evolved to control iron acquisition, storage, and distribution at both systemic and cellular levels. Hepcidin, the master regulator of iron homeostasis, controls iron flows into plasma through inhibition of the only known mammalian cellular iron exporter ferroportin. Hepcidin is feedback-regulated by iron status and strongly modulated by inflammation and erythropoietic demand. This review highlights recent advances that have changed our understanding of iron metabolism and its regulation.

The plasma membrane metal-ion transporter ZIP14 contributes to nontransferrin-bound iron uptake by human ß-cells.

The relationship between iron and ß-cell dysfunction has long been recognized as individuals with iron overload display an increased incidence of diabetes. This link is usually attributed to the accumulation of excess iron in ß-cells leading to cellular damage and impaired function. Yet, the molecular mechanism(s) by which human ß-cells take up iron has not been determined. In the present study, we assessed the contribution of the metal-ion transporters ZRT/IRT-like protein 14 and 8 (ZIP14 and ZIP8) and divalent metal-ion transporter-1 (DMT1) to iron uptake by human ß-cells. Iron was provided to the cells as nontransferrin-bound iron (NTBI), which appears in the plasma during iron overload and is a major contributor to tissue iron loading. We found that overexpression of ZIP14 and ZIP8, but not DMT1, resulted in increased NTBI uptake by ßlox5 cells, a human ß-cell line. Conversely, siRNA-mediated knockdown of ZIP14, but not ZIP8, resulted in 50% lower NTBI uptake in ßlox5 cells. In primary human islets, knockdown of ZIP14 also reduced NTBI uptake by 50%. Immunofluorescence analysis of islets from human pancreatic sections localized ZIP14 and DMT1 nearly exclusively to ß-cells. Studies in primary human islets suggest that ZIP14 protein levels do not vary with iron status or treatment with IL-1ß. Collectively, these observations identify ZIP14 as a major contributor to NTBI uptake by ß-cells and suggest differential regulation of ZIP14 in primary human islets compared with other cell types such as hepatocytes.

SLC39A14 Is Required for the Development of Hepatocellular Iron Overload in Murine Models of Hereditary Hemochromatosis.

Nearly all forms of hereditary hemochromatosis are characterized by pathological iron accumulation in the liver, pancreas, and heart. These tissues preferentially load iron because they take up non-transferrin-bound iron (NTBI), which appears in the plasma during iron overload. Yet, how tissues take up NTBI is largely unknown. We report that ablation of Slc39a14, the gene coding for solute carrier SLC39A14 (also called ZIP14), in mice markedly reduced the uptake of plasma NTBI by the liver and pancreas. To test the role of SLC39A14 in tissue iron loading, we crossed Slc39a14(-/-) mice with Hfe(-/-) and Hfe2(-/-) mice, animal models of type 1 and type 2 (juvenile) hemochromatosis, respectively. Slc39a14 deficiency in hemochromatotic mice greatly diminished iron loading of the liver and prevented iron deposition in hepatocytes and pancreatic acinar cells. The data suggest that inhibition of SLC39A14 may mitigate hepatic and pancreatic iron loading and associated pathologies in iron overload disorders.

Microarray analysis of rat pancreas reveals altered expression of Alox15 and regenerating islet-derived genes in response to iron deficiency and overload.

It is well known that iron overload can result in pancreatic iron deposition, beta-cell destruction, and diabetes in humans. Recent studies in animals have extended the link between iron status and pancreatic function by showing that iron depletion confers protection against beta-cell dysfunction and diabetes. The aim of the present study was to identify genes in the pancreas that are differentially expressed in response to iron deficiency or overload. Weanling male Sprague-Dawley rats (n = 6/group) were fed iron-deficient, iron-adequate, or iron-overloaded diets for 3 weeks to alter their iron status. Total RNA was isolated from the pancreases and pooled within each group for microarray analyses in which gene expression levels were compared to those in iron-adequate controls. In iron-deficient pancreas, a total of 66 genes were found to be differentially regulated (10 up, 56 down), whereas in iron-overloaded pancreas, 164 genes were affected (82 up, 82 down). The most up-regulated transcript in iron-deficient pancreas was arachidonate 15-lipoxygenase (Alox15), which has been implicated in the development of diabetes. In iron-overloaded pancreas, the most upregulated transcripts were Reg1a, Reg3a, and Reg3b belonging to the regenerating islet-derived gene (Reg) family. Reg expression has been observed in response to pancreatic stress and is thought to facilitate pancreatic regeneration. Subsequent qRT-PCR validation indicated that Alox15 mRNA levels were 4 times higher in iron-deficient than in iron-adequate pancreas and that Reg1a, Reg3a, and Reg3b mRNA levels were 17-36 times higher in iron-overloaded pancreas. The elevated Alox15 mRNA levels in iron-deficient pancreas were associated with 8-fold higher levels of Alox15 protein as indicated by Western blotting. Overall, these data raise the possibility that Reg expression may serve as a biomarker for iron-related pancreatic stress, and that iron deficiency may adversely affect the risk of developing diabetes through up-regulation of Alox15.

Implementation of lean thinking: one health system's journey.

BACKGROUND: Lean Thinking is a management philosophy derived from the manufacturing industry, where Toyota has long been the gold standard. Health care organizations have started to apply this approach to patient care. After initial experimentation, the University of Michigan Health System (UMHS) has adopted Lean Thinking as its uniform approach to quality improvement and is striving to become a complete Lean organization. PROJECTS: In 2005, the senior leadership selected an initial set of projects in areas that traced the patient's journey across different care settings within our health system. Four of the projects were as follows: orthopedic surgery clinic scheduling, radiation oncology therapy, peripherally inserted central catheter (PICC) services, and coordination of care to the outpatient setting. LESSONS FROM LEAN THINKING: Lean Thinking encourages service providers to focus on value as defined by the customer and the relentless elimination of waste that impedes the flow of value. A series of learning projects were conducted to test whether Lean methods would work at UMHS. The following factors were found to be key to LEAN PROJECT SUCCESS: expert guidance for initial efforts, leadership in the form of clinical champions and senior management support of the improvement work, frontline worker engagement in mapping out "current state" processes, identifying waste and designing an improved "future state," using metrics to develop and track interventions, and defining realistic project scope. FINAL REFLECTIONS: As UMHS's experience applying Lean Thinking to our patient care processes has grown, so have support, enthusiasm, and expertise within the organization. UMHS's Lean Thinking system, now known as the Michigan Quality System, has emerged as the core improvement strategy.

An introduction to critical paths.

A critical path defines the optimal sequencing and timing of interventions by physicians, nurses, and other staff for a particular diagnosis or procedure. Critical paths are developed through collaborative efforts of physicians, nurses, pharmacists, and others to improve the quality and value of patient care. They are designed to minimize delays and resource utilization and to maximize quality of care. Critical paths have been shown to reduce variation in the care provided, facilitate expected outcomes, reduce delays, reduce length of stay, and improve cost-effectiveness. The approach and goals of critical paths are consistent with those of total quality management (TQM) and can be an important part of an organization's TQM process.