Regenerative medicine: a radical reappraisal of the spleen

The spleen assumes a major role in blood glucose regulation in type 1 diabetes patients treated with BCG

The Bacillus Calmette-Guérin (BCG) vaccine, which has been used for > 100 years to prevent tuberculosis, is well-established for bladder cancer treatment, and under study for neurological and autoimmune diseases. In patients with type 1 diabetes (T1D), BCG vaccinations have been shown in randomized clinical trials to gradually lower blood sugar to near normal levels. This effect appears to be driven by a BCG-induced shift in lymphoid cells' glucose metabolism from oxidative phosphorylation to aerobic glycolysis. The latter is a state of high glucose utilization that draws more glucose from the blood. Apart from blood, it is unknown whether BCG establishes residence in any organs and alters their glucose metabolism. In this two-year-long clinical trial in type 1 diabetics, we use positron emission tomography (PET) and x-ray computed tomography (CT) to map organs that increase their uptake of the glucose analogue 18F-fluorodeoxyglucose (18F-FDG) before versus after BCG vaccinations. We also injected BALB/c mice with BCG to test for the presence of BCG in various organs. Results from both studies point to the spleen as the dominant site for glucose uptake and BCG residence. The human spleen is significant because its 47% increase in 18F-FDG uptake by a large population of lymphocytes and monocytes might help to explain BCG's systemic lowering of blood glucose to near normal levels. Findings suggest that the spleen, triggered by BCG, assumes a critical role in systemic glucose regulation in the absence of a functional pancreas.

Recipient c-Kit Lineage Cells Repopulate Smooth Muscle Cells of Transplant Arteriosclerosis in Mouse Models

Supplemental Digital Content is available in the text.

Rationale:

Transplantation-accelerated arteriosclerosis is one of the major challenges for long-term survival of patients with solid organ transplantation. Although stem/progenitor cells have been implicated to participate in this process, the cells of origin and underlying mechanisms have not been fully defined.

Objective:

The objective of our study was to investigate the role of c-Kit lineage cells in allograft-induced neointima formation and to explore the mechanisms underlying this process.

Methods and Results:

Using an inducible lineage tracing Kit-CreER;Rosa26-tdTomato mouse model, we observed that c-Kit is expressed in multiple cell types in the blood vessels, rather than a specific stem/progenitor cell marker. We performed allograft transplantation between different donor and recipient mice, as well as bone marrow transplantation experiments, demonstrating that recipient c-Kit⁺ cells repopulate neointimal smooth muscle cells (SMCs) and leukocytes, and contribute to neointima formation in an allograft transplantation model. c-Kit–derived SMCs originate from nonbone marrow tissues, whereas bone marrow-derived c-Kit⁺ cells mainly generate CD45⁺ leukocytes. However, the exact identity of c-Kit lineage cells contributing to neointimal SMCs remains unclear. ACK2 (anti-c-Kit antibody), which specifically binds and blocks c-Kit function, ameliorates allograft-induced arteriosclerosis. Stem cell factor and TGF (transforming growth factor)-β1 levels were significantly increased in blood and neointimal lesions after allograft transplantation, by which stem cell factor facilitated c-Kit⁺ cell migration through the stem cell factor/c-Kit axis and downstream activation of small GTPases, MEK (mitogen-activated protein kinase kinase)/ERK (extracellular signal–regulated kinase)/MLC (myosin light chain), and JNK (c-Jun N-terminal kinase)/c-Jun signaling pathways, whereas TGF-β1 induces c-Kit⁺ cell differentiation into SMCs via HK (hexokinase)-1–dependent metabolic reprogramming and a possible downstream O-GlcNAcylation of myocardin and serum response factor.

Conclusions:

Our findings provide evidence that recipient c-Kit lineage cells contribute to vascular remodeling in an allograft transplantation model, in which the stem cell factor/c-Kit axis is responsible for cell migration and HK-1–dependent metabolic reprogramming for SMC differentiation.

Existence of Neural Stem Cells in Mouse Spleen

Pluripotent stem cells are used in regenerative medicine and exist in various internal organs. However, there are a small number of reports of neural cells or neural stem cells existing in the spleen. In this study, we sought to identify possible neural stem cells in the mouse spleen. The spleens of ICR mice were removed and small specimens were incubated in Dulbecco's modified Eagle's medium with Nutrient Mixture F-12 containing either 10% fetal bovine serum (FBS), 20% FBS, 10% neonate bovine serum, or 10% fetal calf serum. Neural cell medium was also used. The cultured cells were investigated for expression of the neural cell markers neuron-specific enolase (NSE) and neurofilament 150 kDa (NF-150) by immunocytochemistry. Mouse spleens were also examined by immunohistochemistry for NSE, NF-150, NF-200, peripherin, and glial fibrillary acidic protein. Cells morphologically resembling neural cells were obtained and were positive for neural cell markers. Some of the cells generated sphere-like formations, which may have been neurospheres. Cell proliferation was best in medium containing 10% FBS. Cells positive for neural markers were observed in the subcapsular and perivascular regions of the spleen. The cells were round and present in much lower numbers than in cell culture. These cells are suspected neural stem cells and would be expected to differentiate into neural cells in cell culture. This report suggests the existence of neural stem cells in the mouse spleen.

Cdc42 Promotes ADSC-Derived IPC Induction, Proliferation, And Insulin Secretion Via Wnt/β-Catenin Signaling

PURPOSE

Type 1 diabetes mellitus (T1DM) is characterized by irreversible islet β cell destruction. Accumulative evidence indicated that Cdc42 and Wnt/β-catenin signaling both play a critical role in the pathogenesis and development of T1DM. Further, bio-molecular mechanisms in adipose-derived mesenchymal stem cells (ADSCs)-derived insulin-producing cells (IPCs) remain largely unknown. Our aim was to investigate the underlying mechanism of Cdc42/Wnt/β-catenin pathway in ADSC-derived IPCs, which may provide new insights into the therapeutic strategy for T1DM patients.

METHODS

ADSC induction was accomplished with DMSO under high-glucose condition. ML141 (Cdc42 inhibitor) and Wnt-3a (Wnt signaling activator) were administered to ADSCs from day 2 until the induction finished. Morphological changes were determined by an inverted microscope. Dithizone staining was employed to evaluate the induction of ADSC-derived IPCs. qPCR and Western blotting were employed to measure the mRNA and protein expression level of islet cell development-related genes and Wnt signaling-related genes. The proliferation ability of ADSC-derived IPCs was also detected with a cell counting kit (CCK) assay. The expression and secretion of Insulin were detected with immunofluorescence test and enzyme-linked immunosorbent assay (ELISA) respectively.

RESULTS

During induction, morphological characters of ADSCs changed into spindle and round shape, and formed islet-line cell clusters, with brown dithizone-stained cytoplasm. Expression levels of islet cell development-related genes were up-regulated in ADSC-derived IPCs. Wnt-3a promoted Wnt signaling markers and islet cell development-related gene expression at mRNA and protein levels, while ML141 played a negative effect. Wnt-3a promoted ADSC-derived IPC proliferation and glucose-stimulated insulin secretion (GSIS), while ML141 played a negative effect.

CONCLUSION

Our research demonstrated that DMSO and high-glucose condition can induce ADSCs into IPCs, and Wnt signaling promotes the induction. Cdc42 may promote IPC induction, IPC proliferation and insulin secretion via Wnt/β-catenin pathway, meaning that Cdc42 may be regarded as a potential target in the treatment of T1DM.

Splenomegaly: Pathophysiological bases and therapeutic options

The spleen is the largest immune organ in the human body and is also essential for red blood cell homeostasis and iron recycling. An average human spleen is approximately 10 centimetres in length and weighs 150g. Pathological conditions can result in the spleen weighing in excess of 2000g and extending over 30 centrimetres in length. This remarkable property of the spleen to expand is termed splenomegaly. Splenomegaly can occur as a physiological response to stress or as a chronic process that is often detrimental to the wellbeing of the individual. Here, we will discuss the normal function and physiology of the spleen, the pathophysiological bases of splenomegaly and the commonly available therapeutic options. Additionally we will address experimental systems to determine the regulatory mechanisms underlying splenomegaly.

The Spleen Is an Ideal Site for Inducing Transplanted Islet Graft Expansion in Mice

Alternative islet transplantation sites have the potential to reduce the marginal number of islets required to ameliorate hyperglycemia in recipients with diabetes. Previously, we reported that T cell leukemia homeobox 1 (Tlx1)+ stem cells in the spleen effectively regenerated into insulin-producing cells in the pancreas of non-obese diabetic mice with end-stage disease. Thus, we investigated the spleen as a potential alternative islet transplantation site. Streptozotocin-induced diabetic C57BL/6 mice received syngeneic islets into the portal vein (PV), beneath the kidney capsule (KC), or into the spleen (SP). The marginal number of islets by PV, KC, or SP was 200, 100, and 50, respectively. Some plasma inflammatory cytokine levels in the SP group were significantly lower than those of the PV group after receiving a marginal number of islets, indicating reduced inflammation in the SP group. Insulin contents were increased 280 days after islet transplantation compared with those immediately following transplantation (p<0.05). Additionally, Tlx1-related genes, including Rrm2b and Pla2g2d, were up-regulated, which indicates that islet grafts expanded in the spleen. The spleen is an ideal candidate for an alternative islet transplantation site because of the resulting reduced inflammation and expansion of the islet graft.

Splenocytes seed bone marrow of myeloablated mice: implication for atherosclerosis

Extramedullary hematopoiesis has been shown to contribute to the pathogenesis of a variety of diseases including cardiovascular diseases. In this process, the spleen is seeded with mobilized bone marrow cells that augment its hematopoietic ability. It is unclear whether these immigrant cells that are produced/reprogrammed in spleen are similar or different from those found in the bone marrow. To begin to understand this, we investigated the relative potency of adult splenocytes per se to repopulate bone marrow of lethally-irradiated mice and its functional consequences in atherosclerosis. The splenocytes were harvested from GFP donor mice and transplanted into myeloablated wild type recipient mice without the inclusion of any bone marrow helper cells. We found that adult splenocytes repopulated bone marrow of myeloablated mice and the transplanted cells differentiated into a full repertoire of myeloid cell lineages. The level of monocytes/macrophages in the bone marrow of recipient mice was dependent on the cell origin, i.e., the donor splenocytes gave rise to significantly more monocytes/macrophages than the donor bone marrow cells. This occurred despite a significantly lower number of hematopoietic stem cells being present in the donor splenocytes when compared with donor bone marrow cells. Atherosclerosis studies revealed that donor splenocytes displayed a similar level of atherogenic and atheroprotective activities to those of donor bone marrow cells. Cell culture studies showed that the phenotype of macrophages derived from spleen is different from those of bone marrow. Together, these results demonstrate that splenocytes can seed bone marrow of myeloablated mice and modulate atherosclerosis. In addition, our study shows the potential of splenocytes for therapeutic interventions in inflammatory disease.

Generation of a Tlx1(CreER-Venus) knock-in mouse strain for the study of spleen development

The spleen is a lymphoid organ that serves as a unique niche for immune reactions, extramedullary hematopoiesis, and the removal of aged erythrocytes from the circulation. While much is known about the immunological functions of the spleen, the mechanisms governing the development and organization of its stromal microenvironment remain poorly understood. Here we report the generation and analysis of a Tlx1(Cre) (ER) (-Venus) knock-in mouse strain engineered to simultaneously express tamoxifen-inducible CreER(T2) and Venus fluorescent protein under the control of regulatory elements of the Tlx1 gene, which encodes a transcription factor essential for spleen development. We demonstrated that Venus as well as CreER expression recapitulates endogenous Tlx1 transcription within the spleen microenvironment. When Tlx1(Cre) (ER) (-Venus) mice were crossed with the Cre-inducible reporter strain, Tlx1-expressing cells as well as their descendants were specifically labeled following tamoxifen administration. We also showed by cell lineage tracing that asplenia caused by Tlx1 deficiency is attributable to altered contribution of mesenchymal cells in the spleen anlage to the pancreatic mesenchyme. Thus, Tlx1(Cre) (ER) (-Venus) mice represent a new tool for lineage tracing and conditional gene manipulation of spleen mesenchymal cells, essential approaches for understanding the molecular mechanisms of spleen development.

Insulin producing cells established using non-integrated lentiviral vector harboring PDX1 gene

AIM: To investigate reprogramming of human adipose tissue derived stem cells into insulin producing cells using non-integrated lentivirus harboring PDX1 gene.

METHODS: In this study, human adipose tissue derived stem cells (hADSCs) were obtained from abdominal adipose tissues by liposuction, selected by plastic adhesion, and characterized by flow cytometric analysis. Human ADSCs were differentiated into adipocytes and osteocytes using differentiating medium to confirm their multipotency. Non-integrated lentiviruses harboring PDX1 (Non-integrated LV-PDX1) were constructed using specific plasmids (pLV-HELP, pMD2G, LV-105-PDX1-1). Then, hADSCs were transduced with non-integrated LV-PDX1. After transduction, ADSCs^PDX1+ were cultured in high glucose DMEM medium supplement by B27, nicotinamide and βFGF for 21 d. Expressions of PDX1 and insulin were detected at protein level by immunofluorescence analysis. Expressions of PDX1, neurogenin3 (Ngn3), glucagon, glucose transporter2 (Glut2) and somatostatin as specific marker genes were investigated at mRNA level by quantitative RT-PCR. Insulin secretion of hADSCs^PDX1+ in the high-glucose medium was detected by electrochemiluminescence test. Human ADSCs^PDX1+ were implanted into hyperglycemic rats.

RESULTS: Human ADSCs exhibited their fibroblast-like morphology and made colonies after 7-10 d of culture. Determination of hADSCs identified by FACS analysis showed that hADSCs were positive for mesenchymal cell markers and negative for hematopoietic cell markers that guaranteed the lack of hematopoietic contamination. In vitro differentiation of hADSCs into osteocytes and adipocytes were detected by Alizarin red and Oil red O staining and confirmed their multilineage differentiation ability. Transduced hADSCs^+PDX1 became round and clusters in the differentiation medium. The appropriate expression of PDX1 and insulin proteins was confirmed using immunocytochemistry analysis. Significant expressions of PDX1, Ngn3, glucagon, Glut2 and somatostatin were detected by quantitative RT-PCR. hADSCs^PDX1+ revealed the glucose sensing ability by expressing Glut2 when they were cultured in the medium containing high glucose concentration. The insulin secretion of hADSCs^PDX1+ in the high glucose medium was 2.32 μU/mL. hADSCs^PDX1+ implantation into hyperglycemic rats cured it two days after injection by reducing blood glucose levels from 485 mg/dL to the normal level.

CONCLUSION: Human ADSCs can differentiate into IPCs by non-integrated LV-PDX1 transduction and have the potential to be used as a resource in type 1 diabetes cell therapy.

Bone marrow-derived cells: A potential approach for the treatment of xerostomia

Transplantations of bone marrow-derived cells (BMDCs) are traditionally used for hematologic diseases, but there are increasing numbers of clinical trials using BMDC treatments for non-hematologic disorders, including autoimmune diseases. BMDCs are recently reported to improve organ functions. This paper will review available reports supporting the role of BMDCs in reducing xerostomia (i.e. re-establishing salivary gland functions) due to head and neck irradiation for cancer therapies and in Sjögren's syndrome. There are reports that BMDCs provide a beneficial effect on the saliva production. BMDCs positively affect blood vessels stability and regeneration in irradiated salivary glands. Also, BMDCs provide an immunomodulatory activity in mice with Sjögren's-like disease. While the exact mechanisms by which BMDCs improve organ functions remain controversial, there is preliminary evidence that a combination of them (such as cell transdifferentiation, vasculogenesis, and paracrine effect) occur in salivary glands.

Stem cells in the spleen: therapeutic potential for Sjogren's syndrome, type I diabetes, and other disorders

The view of the spleen as an unnecessary organ has been shattered. The evidence shows the spleen to be a source of naturally-occurring multipotent stem cells with possibly pluripotent potential. The stem cells are sequestered in the spleen of not only of animals but also of normal human adults. The reservoir of cells is set for differentiation and they need not be manipulated in vitro or ex vivo before autologous or heterologous use. Splenic stem cells, of Hox11 lineage, have been found in disease or injury to differentiate into pancreatic islets, salivary epithelial cells and osteoblast-like cells, cranial neurons, cochlea, lymphocytes, and more differentiated immune cells that repair injured heart cells. Injury or disease in target tissues induces these stem cells, still in the spleen, to upregulate the same embryonic transcription factors artificially introduced into induced pluripotent stem cells (iPS). Splenic stem cells may have broad pluripotent potential, but unlike iPS cells, possess low oncogenic risk.

Proteomics identifies multipotent and low oncogenic risk stem cells of the spleen

The adult spleen harbors a population of naturally occurring multipotent stem cells of non-lymphoid lineage (CD45-). In animal models, these splenic stem cells can directly or indirectly contribute to regeneration of bone, inner ear, cranial nerves, islets, hearts and salivary glands. Here we characterize the CD45- stem cell proteome to determine its potential broader multipotency versus its protection from malignant transformation. Using state-of-the-art proteomics and in vivo testing, we performed functional analyses of unique proteins of CD45- (non-lymphoid) splenic stem cells, as compared with CD45+ (lymphoid) cells. CD45- stem cell-specific proteins were identical to those in iPS, including OCT3/4, SOX2, KLF4, c-MYC and NANOG. They also expressed Hox11, Gli3, Wnt2, and Adam12, the benchmark transcription factors of embryonic stem cells. These transcription factors were functional because their mRNA was upregulated in the spleen in association with ongoing damage to the pancreas and salivary glands, organs to which they normally contribute stem cells. We also show low likelihood of malignant transformation. Our proteomic and functional analyses reveals that naturally occurring CD45- stem cells of the spleen are the first-ever candidates for naturally occurring population of embryonic and iPS cells with low oncogenic risk. Given their presence in normal humans and mice, splenic stem cells are poised for translational research.

Islet Recovery and Reversal of Murine Type 1 Diabetes in the Absence of Any Infused Spleen Cell Contribution

A cure for type 1 diabetes will probably require the provision or elicitation of new pancreatic islet beta cells as well as the reestablishment of immunological tolerance. A 2003 study reported achievement of both advances in the NOD mouse model by coupling injection of Freund's complete adjuvant with infusion of allogeneic spleen cells. It was concluded that the adjuvant eliminated anti-islet autoimmunity and the donor splenocytes differentiated into insulin-producing (presumably beta) cells, culminating in islet regeneration. Here, we provide data indicating that the recovered islets were all of host origin, reflecting that the diabetic NOD mice actually retain substantial beta cell mass, which can be rejuvenated/regenerated to reverse disease upon adjuvant-dependent dampening of autoimmunity.