Restoration of the gut barrier integrity and restructuring of the gut microbiome in aging by angiotensin-(1-7).

Compromised barrier function of colon epithelium with aging is largely due to gut microbial dysbiosis. Recent studies implicate an important role for angiotensin converting enzymes, ACE and ACE2, angiotensins, and the receptors, AT1 receptor (AT1R) and Mas receptor (MasR), in the regulation of colon functions. The present study tested the hypothesis that leaky gut in aging is associated with an imbalance in ACE2/ACE and that the treatment with angiotenisn-(1-7) (Ang-(1-7)) will restore gut barrier integrity and microbiome. Studies were carried out in Young (3-4 months) and old (20-24 months) male mice. Ang-(1-7) was administered by using osmotic pumps. Outcome measures included expressions of ACE, ACE2, AT1R, and MasR, intestinal permeability by using FITC-dextran, and immunohistochemistry of claudin 1 and occludin, and intestinal stem cells (ISCs). ACE2 protein and activity were decreased in Old group while that of ACE were unchanged. Increased intestinal permeability and plasma levels of zonulin-1 in the Old group were normalized by Ang-(1-7). Epithelial disintegrity, reduced number of goblet cells and ISCs in the old group were restored by Ang-(1-7). Expression of claudin 1 and occludin in the aging colon was increased by Ang-(1-7). Infiltration of CD11b+ or F4/80+ inflammatory cells in the old colons were decreased by Ang-(1-7). Gut microbial dysbiosis in aging was evident by decreased richness and altered beta diversity that were reversed by Ang-(1-7) with increased abundance of Lactobacillus or Lachnospiraceae. The present study shows that Ang-(1-7) restores gut barrier integrity and reduces inflammation in the aging colon by restoring the layer of ISCs and by restructuring the gut microbiome.

The role of telomerase reverse transcriptase in the mitochondrial protective functions of Angiotensin-(1-7) in diabetic CD34+ cells.

Angiotensin (Ang)-(1-7) stimulates vasoprotective functions of diabetic (DB) CD34+ hematopoietic stem/progenitor cells partly by decreasing reactive oxygen species (ROS), increasing nitric oxide (NO) levels and decreasing TGFß1 secretion. Telomerase reverse transcriptase (TERT) translocates to mitochondria and regulates ROS generation. Alternative splicing of TERT results in variants α-, ß- and α-ß-TERT, which may oppose functions of full-length (FL) TERT. This study tested if the protective functions of Ang-(1-7) or TGFß1-silencing are mediated by mitoTERT and that diabetes decreases FL-TERT expression by inducing splicing. CD34+ cells were isolated from the peripheral blood mononuclear cells of nondiabetic (ND, n = 68) or DB (n = 74) subjects. NO and mitoROS levels were evaluated by flow cytometry. TERT splice variants and mitoDNA-lesions were characterized by qPCR. TRAP assay was used for telomerase activity. Decoy peptide was used to block mitochondrial translocation (mitoXTERT). TERT inhibitor or mitoXTERT prevented the effects of Ang-(1-7) on NO or mitoROS levels in DB-CD34+ cells. FL-TERT expression and telomerase activity were lower and mitoDNA-lesions were higher in DB cells compared to ND and were reversed by Ang-(1-7) or TGFß1-silencing. The prevalence of TERT splice variants, with predominant ß-TERT expression, was higher and the expression of FL-TERT was lower in DB cells (n = 25) compared to ND (n = 30). Ang-(1-7) or TGFß1-silencing decreased TERT-splicing and increased FL-TERT. Blocking of ß-splicing increased FL-TERT and protected mitoDNA in DB-cells. The findings suggest that diabetes induces TERT-splicing in CD34+ cells and that ß-TERT splice variant largely contributes to the mitoDNA oxidative damage.

Reversal of aging-associated increase in myelopoiesis and expression of alarmins by angiotensin-(1-7).

Aging is associated with chronic systemic inflammation largely due to increased myelopoiesis, which in turn increases risk for vascular disease. We have previously shown evidence for the therapeutic potential of Angiotensin-(1-7) (Ang-(1-7)) in reversing vasoreparative dysfunction in aging. This study tested the hypothesis that ischemic vascular repair in aging by Ang-(1-7) involves attenuation of myelopoietic potential in the bone marrow and decreased mobilization of inflammatory cells. Young or Old male mice of age 3-4 and 22-24 months, respectively, received Ang-(1-7) (1 µg/kg/min, s.c.) for four weeks. Myelopoiesis was evaluated in the bone marrow (BM) cells by carrying out the colony forming unit (CFU-GM) assay followed by flow cytometry of monocyte-macrophages. Expression of pro-myelopoietic factors and alarmins in the hematopoietic progenitor-enriched BM cells was evaluated. Hindlimb ischemia (HLI) was induced by femoral ligation, and mobilization of monocytes into the blood stream was determined. Blood flow recovery was monitored by Laser Doppler imaging and infiltration of inflammatory cells was evaluated by immunohistochemistry. BM cells from Old mice generated a higher number of monocytes (Ly6G-CD11b+Ly6Chi) and M1 macrophages (Ly6ChiF4/80+) compared to that of Young, which was reversed by Ang-(1-7). Gene expression of selected myelopoietic factors, alarmins (S100A8, S100A9, S100A14 and HMGb1) and the receptor for alarmins, RAGE, was higher in the Old hematopoietic progenitor-enriched BM cells compared to the Young. Increased expressions of these factors were decreased by Ang-(1-7). Ischemia-induced mobilization of monocytes was higher in Old mice with decreased blood flow recovery and increased infiltration of monocyte-macrophages compared to the Young, all of which were reversed by Ang-(1-7). Enhanced ischemic vascular repair by Ang-(1-7) in aging is largely by decreasing the generation and recruitment of inflammatory monocyte-macrophages to the areas of ischemic injury. This is associated with decreased alarmin signaling in the BM-hematopoietic progenitor cells.

Transforming growth factor-ß1/Thrombospondin-1/CD47 axis mediates dysfunction in CD34+ cells derived from diabetic older adults.

Aging with diabetes is associated with impaired vasoprotective functions and decreased nitric oxide (NO) generation in CD34+ cells. Transforming growth factor- ß1 (TGF-ß1) is known to regulate hematopoietic functions. This study tested the hypothesis that transforming growth factor- ß1 (TGF-ß1) is upregulated in diabetic CD34+ cells and impairs NO generation via thrombospondin-1 (TSP-1)/CD47/NO pathway. CD34+ cells from nondiabetic (ND) (n=58) or diabetic older adults (DB) (both type 1 and type 2) (n=62) were isolated from peripheral blood. TGF-ß1 was silenced by using an antisense delivered as phosphorodiamidate morpholino oligomer (PMO-TGF-ß1). Migration and proliferation in response to stromal-derived factor-1α (SDF-1α) were evaluated. NO generation and eNOS phosphorylation were determined by flow cytometry. CD34+ cells from older, but not younger, diabetics have higher expression of TGF-ß1 compared to that observed in cells derived from healthy individuals (P<0.05, n=14). TSP-1 expression was higher (n=11) in DB compared to ND cells. TGFß1-PMO decreased the secretion of TGF-ß1, which was accompanied with decreased TSP-1 expression. Impaired proliferation, migration and NO generation in response to SDF-1α in DB cells were reversed by TGF-ß1-PMO (n=6). TSP-1 inhibited migration and proliferation of nondiabetic CD34+ cells that was reversed by CD47-siRNA, which also restored these responses in diabetic CD34+ cells. TSP-1 opposed SDF-1α-induced eNOS phosphorylation at Ser1177 that was reversed by CD47-siRNA. These results infer that increased TGF-ß1 expression in CD34+ cells induces dysfunction in CD34+ cells from diabetic older adults via TSP-1/CD47-dependent inhibition of NO generation.

Blood flow restriction exercise stimulates mobilization of hematopoietic stem/progenitor cells and increases the circulating ACE2 levels in healthy adults.

Adult CD34+ hematopoietic stem/progenitor cells (HSPC) in the systemic circulation are bone marrow-derived and have the propensity of maintaining cardiovascular health. Activation of angiotensin-converting enzyme-2 (ACE2)-angiotensin-(1-7)-Mas receptor pathway, the vascular protective axis of the renin-angiotensin system (RAS), stimulates vasculogenic functions of HSPCs. In a previous study, exposure to hypoxia increased the expressions of ACE2 and Mas, and stimulated ACE2 shedding. The current study tested if blood flow restriction exercise (BFR)-induced regional hypoxia recapitulates the in vitro observations in healthy adults. Hypoxia was induced by 80% limb occlusion pressure (LOP) via inflation cuff. Muscle oxygen saturation was determined using near-infrared spectroscopy. Peripheral blood was collected 30 min after quiet sitting (control) or after BFR. Lin-CD45lowCD34+ HSPCs were enumerated by flow cytometry, and ACE and ACE2 activities were determined in plasma and cell lysates and supernatants. Regional hypoxia resulted in muscle oxygen saturation of 17.5% compared with 49.7% in the control condition (P < 0.0001, n = 9). Circulating HSPCs were increased following BFR (834.8 ± 62.1/mL) compared with control (365 ± 59, P < 0.001, n = 7), which was associated with increased stromal-derived factor 1α and vascular endothelial growth factor receptor levels by four- and threefold, respectively (P < 0.001). ACE2 activity was increased in the whole cell lysates of HSPCs, resulting in an ACE2-to-ACE ratio of 11.7 ± 0.5 in BFR vs 9.1 ± 0.9 in control (P < 0.05). Cell supernatants have threefold increase in the ACE2-to-ACE ratio following BFR compared with control (P < 0.001). Collectively, these findings provide strong evidence for the upregulation of ACE2 by acute regional hypoxia in vivo. Hypoxic exercise regimens appear to be promising means of enhancing vascular regenerative capacity.NEW & NOTEWORTHY Although many studies have explored the mechanisms of skeletal muscle growth and adaptation with hypoxia exercise interventions, less attention has been given to the potential for vascular adaptation and regenerative capacity. This study shows for the first time an acute upregulation of the angiotensin-converting enzyme 2 and increase in CD34+ vasculogenic cells following an acute bout of blood flow restriction with low-intensity exercise. These rapid changes collectively promote skeletal muscle angiogenesis. Therefore, this study supports the potential of hypoxic exercise interventions with low intensity for vascular and muscle health.