Ectopic Expression of Neurod1 Is Sufficient for Functional Recovery following a Sensory-Motor Cortical Stroke.

Stroke is the leading cause of adult disability worldwide. The majority of stroke survivors are left with devastating functional impairments for which few treatment options exist. Recently, a number of studies have used ectopic expression of transcription factors that direct neuronal cell fate with the intention of converting astrocytes to neurons in various models of brain injury and disease. While there have been reports that question whether astrocyte-to-neuron conversion occurs in vivo, here, we have asked if ectopic expression of the transcription factor Neurod1 is sufficient to promote improved functional outcomes when delivered in the subacute phase following endothelin-1-induced sensory-motor cortex stroke. We used an adeno-associated virus to deliver Neurod1 from the short GFAP promoter and demonstrated improved functional outcomes as early as 28 days post-stroke and persisting to at least 63 days post-stroke. Using Cre-based cell fate tracking, we showed that functional recovery correlated with the expression of neuronal markers in transduced cells by 28 days post-stroke. By 63 days post-stroke, the reporter-expressing cells comprised ~20% of all the neurons in the perilesional cortex and expressed markers of cortical neuron subtypes. Overall, our findings indicate that ectopic expression of Neurod1 in the stroke-injured brain is sufficient to enhance neural repair.

Integrating single-cell and spatially resolved transcriptomic strategies to survey the astrocyte response to stroke in male mice.

Astrocytes, a type of glial cell in the central nervous system (CNS), adopt diverse states in response to injury that are influenced by their location relative to the insult. Here, we describe a platform for spatially resolved, single-cell transcriptomics and proteomics, called tDISCO (tissue-digital microfluidic isolation of single cells for -Omics). We use tDISCO alongside two high-throughput platforms for spatial (Visium) and single-cell transcriptomics (10X Chromium) to examine the heterogeneity of the astrocyte response to a cortical ischemic stroke in male mice. We show that integration of Visium and 10X Chromium datasets infers two astrocyte populations, proximal or distal to the injury site, while tDISCO determines the spatial boundaries and molecular profiles that define these populations. We find that proximal astrocytes show differences in lipid shuttling, with enriched expression of Apoe and Fabp5. Our datasets provide a resource for understanding the roles of astrocytes in stroke and showcase the utility of tDISCO for hypothesis-driven, spatially resolved single-cell experiments.

Highly efficient reprogrammable mouse lines with integrated reporters to track the route to pluripotency.

Revealing the molecular events associated with reprogramming different somatic cell types to pluripotency is critical for understanding the characteristics of induced pluripotent stem cell (iPSC) therapeutic derivatives. Inducible reprogramming factor transgenic cells or animals-designated as secondary (2°) reprogramming systems-not only provide excellent experimental tools for such studies but also offer a strategy to study the variances in cellular reprogramming outcomes due to different in vitro and in vivo environments. To make such studies less cumbersome, it is desirable to have a variety of efficient reprogrammable mouse systems to induce successful mass reprogramming in somatic cell types. Here, we report the development of two transgenic mouse lines from which 2° cells reprogram with unprecedented efficiency. These systems were derived by exposing primary reprogramming cells containing doxycycline-inducible Yamanaka factor expression to a transient interruption in transgene expression, resulting in selection for a subset of clones with robust transgene response. These systems also include reporter genes enabling easy readout of endogenous Oct4 activation (GFP), indicative of pluripotency, and reprogramming transgene expression (mCherry). Notably, somatic cells derived from various fetal and adult tissues from these 2° mouse lines gave rise to highly efficient and rapid reprogramming, with transgene-independent iPSC colonies emerging as early as 1 wk after induction. These mouse lines serve as a powerful tool to explore sources of variability in reprogramming and the mechanistic underpinnings of efficient reprogramming systems.

The gut hormone receptor GIPR links energy availability to the control of hematopoiesis.

OBJECTIVE: Glucose-dependent insulinotropic polypeptide (GIP) conveys information from ingested nutrients to peripheral tissues, signaling energy availability. The GIP Receptor (GIPR) is also expressed in the bone marrow, notably in cells of the myeloid lineage. However, the importance of gain and loss of GIPR signaling for diverse hematopoietic responses remains unclear. METHODS: We assessed the expression of the Gipr in bone marrow (BM) lineages and examined functional roles for the GIPR in control of hematopoiesis. Bone marrow responses were studied in (i) mice fed regular or energy-rich diets, (ii) mice treated with hematopoietic stressors including acute 5-fluorouracil (5-FU), pamsaccharide (LPS), and Pam3CysSerLys4 (Pam3CSK4), with or without pharmacological administration of a GIPR agonist, and (iii) mice with global (Gipr-/-) or selective deletion of the GIPR (GiprTie2-/-) with and without bone marrow transplantation (BMT). RESULTS: Gipr is expressed within T cells, myeloid cells, and myeloid precursors; however, these cell populations were not different in peripheral blood, spleen, or BM of Gipr-/- and GiprTie2-/- mice. Nevertheless, gain and loss of function studies revealed that GIPR signaling controls the expression of BM Toll-like receptor (TLR) and Notch-related genes regulating hematopoiesis. Loss of the BM GIPR attenuates the extent of adipose tissue inflammation and dysregulates the hematopoietic response to BMT. GIPR agonism modified BM gene expression profiles following 5-FU and Pam3CSK4 whereas loss of the Gipr altered the hematopoietic responses to energy excess, two TLR ligands, and 5-FU. However, the magnitude of the cellular changes in hematopoiesis in response to gain or loss of GIPR signaling was relatively modest. CONCLUSION: These studies identify a functional gut hormone-BM axis positioned for the transduction of signals linking nutrient availability to the control of TLR and Notch genes regulating hematopoiesis. Nevertheless, stimulation or loss of GIPR signaling has minimal impact on basal hematopoiesis or the physiological response to hematopoietic stress.

Analysis of procoagulant phosphatidylserine-exposing platelets by imaging flow cytometry.

BACKGROUND: Upon platelet activation, a subpopulation of procoagulant platelets is formed, characterized by the exposure of the anionic aminophospholipid phosphatidylserine (PS) on the surface membrane. OBJECTIVE: To evaluate procoagulant PS-exposing platelets by imaging flow cytometry. METHODS: Platelet ultrastructure was examined by transmission electron microscopy, and a comprehensive analysis of procoagulant platelets was performed using imaging flow cytometry; platelets were fluorescently labeled for the markers glycoprotein (GP)IX, activated integrin αIIbß3, CD62P, and PS exposure. RESULTS: A subpopulation of platelets stimulated in suspension by the physiological agonists thrombin+collagen, and all platelets stimulated by the calcium ionophore A23187, had a distinct round morphology. These platelets were PS-exposing, larger in size, had an increased circularity index, and had reduced internal complexity compared with non-PS-exposing platelets. They expressed CD62P and αIIbß3 in an inactive conformation on the surface, and demonstrated depolarized inner mitochondrial membranes. For the first time, using imaging flow cytometry, a large proportion of PS-exposing platelets possessing platelet-associated extracellular vesicles (EVs) was observed, which demonstrated heterogeneous platelet marker expression that was different from free released EVs. CONCLUSIONS: Innovative imaging flow cytometry allowed detailed fluorescence-based, quantitative morphometric analysis of PS-exposing platelets; in becoming procoagulant, platelets undergo remarkable morphological changes, transforming into spherical "balloons," almost devoid of their normal internal architecture. Almost all PS-exposing platelets have associated EVs that are not detectable by traditional flow cytometry. While their functions have yet to be fully elucidated, the heterogeneity of platelet-associated and released EVs suggests that they may contribute to different aspects of hemostasis and of thrombosis.

Young steady-state rabbit platelets do not have an enhanced capacity to expose procoagulant phosphatidylserine.

Platelets are recognized to be physiologically and functionally heterogeneous. An example of the diversity in reactivity is the formation of a distinct subpopulation of procoagulant phosphatidylserine (PS)-exposing platelets upon activation. Platelet age has been proposed as a determinant of platelet function, and it has been reported that young platelets are more reactive in exposing PS; using the same methodology of thiazole orange (TO) staining to distinguish young and old platelets, the percentages of procoagulant platelets produced by thrombin plus collagen activation of platelets from healthy controls were examined by flow cytometry. The procoagulant subpopulation formed by TO-positive platelets (with high TO fluorescence), purported to be young reticulated platelets, was observed to be significantly larger than that formed by TO-negative platelets (with low TO fluorescence), purported to be older platelets. However, it was noted that TO fluorescence in the total platelet population was unimodal and increased with platelet size, assessed by forward scatter. This observation raised the concern that TO-positive platelets are not necessarily the youngest platelets in the condition of steady-state platelet production. Thus, to unequivocally determine whether platelet age is a factor in procoagulant platelet formation, a different approach to identify young, steady-state platelets was employed. Rabbits were injected with biotin to label >95% of circulating platelets in vivo; 24 hours post-biotinylation, the non-biotinylated platelets in the circulation, detected flow cytometrically, are the youngest, newly-formed platelets. It was demonstrated that these youngest platelets were not larger in size than older, biotinylated platelets, and that they did not have an enhanced capacity to expose PS.

Cellular Sites and Mechanisms Linking Reduction of Dipeptidyl Peptidase-4 Activity to Control of Incretin Hormone Action and Glucose Homeostasis.

Pharmacological inhibition of the dipeptidyl peptidase-4 (DPP4) enzyme potentiates incretin action and is widely used to treat type 2 diabetes. Nevertheless, the precise cells and tissues critical for incretin degradation and glucose homeostasis remain unknown. Here, we use mouse genetics and pharmacologic DPP4 inhibition to identify DPP4+ cell types essential for incretin action. Although enterocyte DPP4 accounted for substantial intestinal DPP4 activity, ablation of enterocyte DPP4 in Dpp4Gut-/- mice did not produce alterations in plasma DPP4 activity, incretin hormone levels, and glucose tolerance. In contrast, endothelial cell (EC)-derived DPP4 contributed substantially to levels of soluble plasma DPP4 activity, incretin degradation, and glucose control. Surprisingly, DPP4+ cells of bone marrow origin mediated the selective degradation of fasting GIP, but not GLP-1. Collectively, these findings identify distinct roles for DPP4 in the EC versus the bone marrow compartment for selective incretin degradation and DPP4i-mediated glucoregulation.

Inhibition of Dipeptidyl Peptidase-4 Impairs Ventricular Function and Promotes Cardiac Fibrosis in High Fat-Fed Diabetic Mice.

Dipeptidyl peptidase-4 (DPP4) inhibitors used for the treatment of type 2 diabetes are cardioprotective in preclinical studies; however, some cardiovascular outcome studies revealed increased hospitalization rates for heart failure (HF) among a subset of DPP4 inhibitor-treated subjects with diabetes. We evaluated cardiovascular function in young euglycemic Dpp4(-/-) mice and in older, high fat-fed, diabetic C57BL/6J mice treated with either the glucagon-like peptide 1 receptor (GLP-1R) agonist liraglutide or the highly selective DPP4 inhibitor MK-0626. We assessed glucose metabolism, ventricular function and remodeling, and cardiac gene expression profiles linked to inflammation and fibrosis after transverse aortic constriction (TAC) surgery, a pressure-volume overload model of HF. Young euglycemic Dpp4(-/-) mice exhibited a cardioprotective response after TAC surgery or doxorubicin administration, with reduced fibrosis; however, cardiac mRNA analysis revealed increased expression of inflammation-related transcripts. Older, diabetic, high fat-fed mice treated with the GLP-1R agonist liraglutide exhibited preservation of cardiac function. In contrast, diabetic mice treated with MK-0626 exhibited modest cardiac hypertrophy, impairment of cardiac function, and dysregulated expression of genes and proteins controlling inflammation and cardiac fibrosis. These findings provide a model for the analysis of mechanisms linking fibrosis, inflammation, and impaired ventricular function to DPP4 inhibition in preclinical studies.

Adult Neural Stem Cells from the Subventricular Zone Give Rise to Reactive Astrocytes in the Cortex after Stroke.

Reactive astrocytes (RAs) have been reported to convert to multipotent neural stem cells (NSCs) capable of neurosphere (NS) formation and multilineage differentiation in vitro. Using genetic tagging, we determined that subventricular zone (SVZ) NSCs give rise to NSs derived from the stroke-injured cortex. We demonstrate that these cells can be isolated from the cortex in two different models of stroke and from different stroke-lesioned cortical regions. Interestingly, SVZ NSCs give rise to a subpopulation of RAs in the cortex that contribute to astrogliosis and scar formation. Last, we show that these SVZ derived RAs can be converted to neurons in vivo by forced expression of Ascl1. Identifying the contribution of cells originating from the SVZ to injury repair has implications for neural regeneration strategies.

GLP-1R Agonists Modulate Enteric Immune Responses Through the Intestinal Intraepithelial Lymphocyte GLP-1R.

Obesity and diabetes are characterized by increased inflammation reflecting disordered control of innate immunity. We reveal a local intestinal intraepithelial lymphocyte (IEL)-GLP-1 receptor (GLP-1R) signaling network that controls mucosal immune responses. Glp1r expression was enriched in intestinal IEL preparations and copurified with markers of Tαß and Tγδ IELs, the two main subsets of intestinal IELs. Exendin-4 increased cAMP accumulation in purified IELs and reduced the production of cytokines from activated IELs but not from splenocytes ex vivo. These actions were mimicked by forskolin, absent in IELs from Glp1r(-/-) mice, and attenuated by the GLP-1R agonist exendin (9-39) consistent with a GLP-1R-dependent mechanism of action. Furthermore, Glp1r(-/-) mice exhibited dysregulated intestinal gene expression, an abnormal representation of microbial species in feces, and enhanced sensitivity to intestinal injury following administration of dextran sodium sulfate. Bone marrow transplantation using wild-type C57BL/6 donors normalized expression of multiple genes regulating immune function and epithelial integrity in Glp1r(-/-) recipient mice, whereas acute exendin-4 administration robustly induced the expression of genes encoding cytokines and chemokines in normal and injured intestine. Taken together, these findings define a local enteroendocrine-IEL axis linking energy availability, host microbial responses, and mucosal integrity to the control of innate immunity.

Phosphatidylserine exposure and other apoptotic-like events in Bernard-Soulier syndrome platelets.

In the Bernard-Soulier syndrome (BSS), the giant platelets are said to have increased phosphatidylserine (PS) surface exposure in the resting state and shortened survival in the circulation. When normal platelets are activated, they undergo many biochemical and morphological changes, some of which are apoptotic. Herein, we investigated apoptotic-like events in BSS platelets upon activation, specifically, PS exposure, microparticle (MP) formation, cell shrinkage, and loss of mitochondrial inner membrane potential (DeltaPsi(m)). Platelets from two unrelated BSS patients were examined in whole blood; agonists used were collagen, thrombin, PAR1- or PAR4-activating peptides (APs), or combinations of collagen with thrombin, and the PAR-APs. Flow cytometry was used to measure PS exposure (annexin A5 binding), platelet-derived MPs (forward scatter; events <0.75 microm size), and DeltaPsi(m) (TMRM fluorescence). PS exposure was increased on resting and activated BSS platelets, and this was independent of the platelet size. MP formation by BSS platelets was generally enhanced. Cell shrinkage occurred on activation to form smaller, PS-exposing platelets in BSS and controls. A proportion of PS-exposing BSS and control platelets exhibited DeltaPsi(m) loss, but unlike controls, there was also loss of DeltaPsi(m) in the BSS platelets not exposing PS. Thus, BSS platelets undergo apoptotic-like events upon activation, with PS exposure and MP formation being enhanced. These events may play a role in the shortened survival in BSS, as well as affecting thrombin generation.

Effects of distal embolization on the timing of platelet and inflammatory cell activation in interventional coronary no-reflow.

INTRODUCTION: Myocardial hypoperfusion following percutaneous coronary intervention, termed "no-reflow", may be initiated by distal coronary embolization. This study examined the effects of distal embolization on the extent and timing of inflammation and platelet activation in an experimental model of coronary no-reflow. MATERIAL AND METHODS: A no-reflow model was established in 9 Yorkshire pigs by injecting incremental doses of biologically inert polystyrene microspheres into the left anterior descending artery every 20 minutes via a transit catheter. A control group included 3 pigs that received corresponding intra-coronary boluses of normal saline. At predefined time points, coronary sinus blood samples were drawn and immediately analyzed by flow cytometry analysis for a panel of white blood cell and platelet activation markers, and the inflammatory cytokine TNFalpha. RESULTS: No-reflow was achieved after delivery of 1,169,000+/-303,000 (range: 680,000 to 2,600,000) microspheres. In the distal embolization group, there were significant increases above baseline values in polymorphonuclear-platelet aggregates (146%-218%), in monocyte-platelet aggregates (51%-94%) and in TNFalpha levels (54%-84%) at multiple time points prior to no- reflow (15% cumulative dose and higher). For Annexin A5, there was a significant increase at 52% of cumulative dose (177% above baseline). Controls only showed one significant increase above baseline value for polymorphonuclear-platelet aggregates at the time of the last injection. CONCLUSIONS: Widespread activation of interacting inflammatory and coagulation pathways following microsphere embolization occurred prior to the onset of angiographic no-reflow. This activation pattern cannot be attributed to prolonged coronary sinus instrumentation. Interactions between white blood cells (polymorphonuclears and monocytes) and platelets likely play an important role in the pathogenesis of no-reflow following distal embolization and may represent important therapeutic targets.

Calpain inhibition by calpeptin does not prevent APLT activity reduction in PS-exposing platelets, but calpeptin has independent pro-apoptotic effects.

Exposure of procoagulant phosphatidylserine (PS) on the surface of activated platelets is not readily reversible and this may propagate thrombosis. Persistence of PS exposure may be attributed, at least in part, to a continued reduction of the activity of aminophospholipid translocase (APLT), that transports PS from the outer to the inner membrane leaflet. We investigated whether calpain is involved in the inhibition of APLT activity. In flow cytometric investigations, using the inhibitors calpeptin or E64d at a concentration that blocks calpain activation, we found that calpain is not responsible for the reduction in APLT activity that results in persistence of PS exposure. Unexpectedly, we found that the inhibitors had additional effects independent of blocking calpain. Incubation of resting platelets with calpeptin resulted in a subpopulation of platelets with increased intracellular Ca(2+) and persistent PS exposure. The inhibitors also increased the proportion of platelets with persistent PS exposure in suspensions stimulated with thrombin and/or collagen or the Ca(2+)-ionophore A23187 under conditions in which calpain was not activated or in which its activation was completely blocked; P-selectin expression on thrombin and/or collagen-stimulated platelets was inhibited. Furthermore, in stimulated platelets, calpeptin increased the proportion of the PS-exposing platelets expressing a second apoptotic hallmark, collapsed mitochondrial inner membrane potential (DeltaPsi(m)). These additional effects of calpeptin on platelet regulation of intracellular Ca(2+) levels and apoptotic-like events should be taken into account when it is used as an inhibitor of calpain.

Amplified inflammatory response to sequential hemorrhage, resuscitation, and pulmonary fat embolism: an animal study.

BACKGROUND: The objective of this study was to assess the role of pulmonary fat embolism caused by intramedullary pressurization of the femoral canal in the development of acute lung injury in the setting of acute hemorrhagic shock and resuscitation. METHODS: Thirty New Zealand White rabbits were randomly assigned to one of four groups: (1) nine animals in which hemorrhagic shock was induced by carotid bleeding, resuscitation was performed, and the femoral canal was reamed and pressurized with bone cement to induce fat embolism (hemorrhagic shock and resuscitation/fat embolism [HR/FE] group); (2) six animals in which shock was induced by carotid bleeding, resuscitation was performed, and a sham knee incision was made and closed without drilling, reaming, or pressurization (hemorrhagic shock and resuscitation [HR] group); (3) eight animals in which no hemorrhage or shock was induced but the femoral canal was reamed and pressurized with bone cement to induce fat embolism (fat embolism [FE] group); and (4) seven animals that had a three-hour ventilation period followed by a sham knee incision (control group). The animals were ventilated for four hours following closure. Flow cytometry with use of antibodies against CD45 and CD11b was performed to test neutrophil activation in whole blood. Histological examination of lung specimens was also performed. Plasma and bronchoalveolar lavage fluid were analyzed for monocyte chemotactic peptide-1 and interleukin-8 levels with use of the ELISA (enzyme-linked immunosorbent assay) method. RESULTS: Three animals in the HR/FE group died immediately after canal pressurization and were excluded. CD11b mean channel fluorescence was significantly elevated, as compared with baseline, only in the HR/FE group at two hours (p = 0.025) and four hours (p = 0.024) after knee closure. Histological analysis showed that only the HR/FE (p < 0.001) and HR (p = 0.010) groups had significantly greater infiltration of alveoli by polymorphonuclear leukocytes as compared with that in the controls. No significant differences in plasma cytokine levels were found between the groups. Only the HR/FE group had significantly higher interleukin-8 (p = 0.020) and monocyte chemotactic peptide-1 (p = 0.004) levels in the bronchoalveolar lavage fluid as compared with those in the controls. CONCLUSIONS: Fat embolism from canal pressurization alone did not activate a pulmonary inflammatory response. The combination of hemorrhagic shock, resuscitation, and fat embolism elicited neutrophil activation, infiltration of alveoli by polymorphonuclear leukocytes, and inflammatory cytokine expression in bronchoalveolar lavage fluid.

Adiponectin deficiency promotes endothelial activation and profoundly exacerbates sepsis-related mortality.

Sepsis is a multifactorial, and often fatal, disorder typically characterized by widespread inflammation and immune activation with resultant endothelial activation. In the present study, we postulated that the adipokine adiponectin serves as a critical modulator of survival and endothelial activation in sepsis. To this aim, we evaluated both loss-of-function (adiponectin gene-deficient mice) and subsequent gain-of-function (recombinant adiponectin reconstitution) strategies in two well-established inflammatory models, cecal ligation perforation (CLP) and thioglyocollate-induced peritonitis. Adipoq(-/-) mice, subjected to CLP, exhibited a profound ( approximately 8-fold) reduction in survival compared with their wild-type Adipoq(+/+) littermates after 48 h. Furthermore, compared with wild-type controls, thioglycollate challenge resulted in a markedly greater influx of peritoneal neutrophils in Adipoq(-/-) mice accompanied by an excess production of key chemoattractant cytokines (IL-12p70, TNFalpha, MCP-1, and IL-6) and upregulation of aortic endothelial adhesion molecule VCAM-1 and ICAM-1 expressions. Importantly, all of these effects were blunted by recombinant total adiponectin administration given 3 days prior to thioglycollate challenge. The protective effects of adiponectin were ascribed largely to higher-order adiponectin oligomers, since administration of recombinant C39A trimeric adiponectin did not attenuate endothelial adhesion molecule expression in thioglycollate-challenged Adipoq(-/-) mice. These data suggest a critical role of adiponectin as a modulator of survival and endothelial inflammation in experimental sepsis and a potential mechanistic link between adiposity and increased sepsis.

Platelet Toll-like receptor expression modulates lipopolysaccharide-induced thrombocytopenia and tumor necrosis factor-alpha production in vivo.

Toll-like receptors (TLRs) play a critical role in stimulating innate immunity by recognizing pathogen-associated molecular patterns (PAMPs) on invading microorganisms. Platelets also play a role in innate immunity, and we studied whether they express TLR. Results show that human and murine platelets variably expressed TLR2, TLR4, and TLR9 by flow cytometry and Western blotting. TLR4 expression was confirmed by demonstrating murine platelet binding to lipopolysaccharide (LPS). Thrombin activation of the platelets significantly enhanced the expression of TLR9, suggesting that at least some TLRs may derive from intracellular compartments. When LPS was administered to LPS-sensitive C3H/HeN and LPS-resistant C3H/HeJ mice, functional TLR4 expression in vivo was shown to be responsible for LPS-induced thrombocytopenia. However, when the C3H/HeN mice were first rendered thrombocytopenic by an antiplatelet antibody and then administered LPS, a significant reduction occurred in their ability to produce TNF-alpha. The decreased cytokine production in the thrombocytopenic mice was restored with platelet transfusion. These results suggest that platelets express various TLRs and that the functional significance of one of these, TLR4, appears to be a role in the modulation of LPS-induced thrombocytopenia and TNF-alpha production. This work implicates platelets as important mediators of innate immune responses against invading microorganisms.