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 TGFβ1 secretion. Telomerase reverse transcriptase (TERT) translocates to mitochondria and regulates ROS generation. Alternative splicing of TERT results in variants α-, β- and α-β-TERT, which may oppose functions of full-length (FL) TERT. This study tested if the protective functions of Ang-(1-7) or TGFβ1-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 TGFβ1-silencing. The prevalence of TERT splice variants, with predominant β-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 TGFβ1-silencing decreased TERT-splicing and increased FL-TERT. Blocking of β-splicing increased FL-TERT and protected mitoDNA in DB-cells. The findings suggest that diabetes induces TERT-splicing in CD34+ cells and that β-TERT splice variant largely contributes to the mitoDNA oxidative damage.

Integrin β1 is a key determinant of the expression of angiotensin-converting enzyme 2 (ACE2) in the kidney epithelial cells

The expression of the angiotensin-converting enzyme 2 (ACE2) is altered in multiple chronic kidney diseases like hypertension and renal fibrosis, where the signaling from the basal membrane proteins is critical for the development and progression of the various pathologies. Integrins are heterodimeric cell surface receptors that have important roles in the progression of these chronic kidney diseases by altering various cell signaling pathways in response to changes in the basement membrane proteins. It is unclear whether integrin or integrin-mediated signaling affects the ACE2 expression in the kidney. The current study tests the hypothesis that integrin β1 regulates the expression of ACE2 in kidney epithelial cells. The role of integrin β1 in ACE2 expression in renal epithelial cells was investigated by shRNA-mediated knockdown and pharmacological inhibition. In vivo studies were carried out using epithelial cell-specific deletion of integrin β1 in the kidneys. Deletion of integrin β1 from the mouse renal epithelial cells reduced the expression of ACE2 in the kidney. Furthermore, the downregulation of integrin β1 using shRNA decreased ACE2 expression in human renal epithelial cells. ACE2 expression levels were also decreased in renal epithelial cells and cancer cells when treated with an integrin α2β1 antagonist, BTT 3033. SARS-CoV-2 viral entry to human renal epithelial cells and cancer cells was also inhibited by BTT 3033. This study demonstrates that integrin β1 positively regulates the expression of ACE2, which is required for the entry of SARS-CoV-2 into kidney cells.

ACE2/ACE imbalance and impaired vasoreparative functions of stem/progenitor cells in aging

Aging increases risk for ischemic vascular diseases. Bone marrow–derived hematopoietic stem/progenitor cells (HSPCs) are known to stimulate vascular regeneration. Activation of either the Mas receptor (MasR) by angiotensin-(1-7) (Ang-(1-7)) or angiotensin-converting enzyme-2 (ACE2) stimulates vasoreparative functions in HSPCs. This study tested if aging is associated with decreased ACE2 expression in HSPCs and if Ang-(1-7) restores vasoreparative functions. Flow cytometric enumeration of Lin⁻CD45^lowCD34⁺ cells was carried out in peripheral blood of male or female individuals (22–83 years of age). Activity of ACE2 or the classical angiotensin-converting enzyme (ACE) was determined in lysates of HSPCs. Lin⁻Sca-1⁺cKit⁺ (LSK) cells were isolated from young (3–5 months) or old (20–22 months) mice, and migration and proliferation were evaluated. Old mice were treated with Ang-(1-7), and mobilization of HSPCs was determined following ischemia induced by femoral ligation. A laser Doppler blood flow meter was used to determine blood flow. Aging was associated with decreased number (Spearman r = − 0.598, P < 0.0001, n = 56), decreased ACE2 (r = − 0.677, P < 0.0004), and increased ACE activity (r = 0.872, P < 0.0001) (n = 23) in HSPCs. Migration or proliferation of LSK cells in basal or in response to stromal-derived factor-1α in old cells is attenuated compared to young, and these dysfunctions were reversed by Ang-(1-7). Ischemia increased the number of circulating LSK cells in young mice, and blood flow to ischemic areas was recovered. These responses were impaired in old mice but were restored by treatment with Ang-(1-7). These results suggest that activation of ACE2 or MasR would be a promising approach for enhancing ischemic vascular repair in aging.

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^-CD45^lowCD34⁺ 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.

Diabetic pre-programming of myelopoiesis impairs tissue repair

Bone marrow-derived monocyte-macrophages promote healing of injured tissue cooperatively with vasculogenic hematopoietic stem/progenitor cells. However, diabetes dysregulates hematopoiesis and attenuates bone marrow-derived tissue-reparative responses. In a recent issue of The Journal of Pathology, Barman et al extensively characterized myelopoietic responses in bone marrow following skin wounding in a type 2 model of diabetes. The study demonstrated that accumulation of monocyte-macrophages in the peripheral tissues is increased due to diabetic myelopoiesis that would oppose the reparative process following tissue injury. Interestingly, in this model, pathological myelopoiesis is independent of IL-1β. The potential prophylactic and therapeutic implications of these data are discussed in terms of paracrine signaling, macrophage polarization, and hematopoietic stem cell mobilization/retention. © 2019 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Hypoxic regulation of angiotensin-converting enzyme 2 and Mas receptor in human CD34+ cells

CD34⁺ hematopoietic stem/progenitor cells (HSPCs) are vasculogenic and hypoxia is a strong stimulus for the vasoreparative functions of these cells. Angiotensin-converting enzyme 2 (ACE2)/angiotensin-(1-7)/Mas receptor (MasR) pathway stimulates vasoprotective functions of CD34⁺ cells. This study tested if ACE2 and MasR are involved in the hypoxic stimulation of CD34⁺ cells. Cells were isolated from circulating mononuclear cells derived from healthy subjects (n = 46) and were exposed to normoxia (20% O₂ ) or hypoxia (1% O₂ ). Luciferase reporter assays were carried out in cells transduced with lentivirus carrying ACE2- or MasR- or a scramble-3'-untranslated region gene with a firefly luciferase reporter. Expressions or activities of ACE, angiotensin receptor Type 1 (AT1R), ACE2, and MasR were determined. In vitro observations were verified in HSPCs derived from mice undergoing hindlimb ischemia (HLI). In vitro exposure to hypoxia-increased proliferation and migration of CD34⁺ cells in basal conditions or in response to vascular endothelial growth factor (VEGF) or stromal-derived factor 1α (SDF) compared with normoxia. Expression of ACE2 or MasR was increased relative to normoxia while ACE or AT1R expressions were unaltered. Luciferase activity was increased by hypoxia in cells transfected with the luciferase reporter plasmids coding for the ACE2- or MasR promoters relatively to the control. The effects of hypoxia were mimicked by VEGF or SDF under normoxia. Hypoxia-induced ADAM17-dependent shedding of functional ACE2 fragments. In mice undergoing HLI, increased expression/activity of ACE2 and MasR were observed in the circulating HSPCs. This study provides compelling evidence for the hypoxic upregulation of ACE2 and MasR in CD34⁺ cells, which likely contributes to vascular repair.

Angiotensin converting enzyme versus angiotensin converting enzyme-2 selectivity of MLN-4760 and DX600 in human and murine bone marrow-derived cells

Angiotensin-converting enzymes, ACE and ACE2, are key members of renin angiotensin system. Activation of ACE2/Ang-(1-7) pathway enhances cardiovascular protective functions of bone marrow-derived stem/progenitor cells. The current study evaluated the selectivity of ACE2 inhibitors, MLN-4760 and DX-600, and ACE and ACE2 activities in human (hu) and murine (mu) bone marrow cells. Assays were carried out in hu and mu mononuclear cells (MNCs) and huCD34(+) cells or mu-lineage-depleted (muLin(-)) cells, human-recombinant (rh) enzymes, and mu-heart with enzyme-specific substrates. ACE or ACE2 inhibition by racemic MLN-4760, its isomers MLN-4760-A and MLN-4760-B, DX600 and captopril were characterized. MLN-4760-B is relatively less efficacious and less-selective than the racemate or MLN-4760-A at hu-rhACE2, and all three of them inhibited 43% rhACE. In huMNCs, MLN-4760-B detected 63% ACE2 with 28-fold selectivity over ACE. In huCD34(+) cells, MLN-4760-B detected 38% of ACE2 activity with 63-fold selectivity. In mu-heart and muMNCs, isomer B was 100- and 228-fold selective for ACE2, respectively. In muLin(-) cells, MLN-4760-B detected 25% ACE2 activity with a pIC50 of 6.3. The racemic mixture and MLN-4760-A showed lower efficacy and poor selectivity for ACE2 in MNCs and mu-heart. ACE activity detected by captopril was 32% and 19%, respectively, in huCD34(+) and muLin(-) cells. DX600 was less efficacious, and more selective for ACE2 compared to MLN-4760-B in all samples tested. These results suggest that MLN-4760-B is a better antagonist of ACE2 than DX600 at 10 µm concentration in human and murine bone marrow cells, and that these cells express more functional ACE2 than ACE.

Functional characterization of alpha1-adrenoceptor subtypes in human subcutaneous resistance arteries

The functional characteristics of the alpha1-adrenoceptor subtypes in human resistance arteries are still not clear. We recently reported that the alpha1A-adrenoceptor predominantly mediates contraction to norepinephrine in human skeletal muscle resistance arteries. In this study we extended these investigations to human subcutaneous resistance arteries. Arterial segments were isolated from the inguinal subcutaneous fat and mounted on a small vessel wire myograph. Potencies of agonists and antagonists were examined. N-[5-(4,5-dihydro-1H-imidazol-2yl)-2-hydroxy-5,6,7,8-tetrahydronaphthalen-1-yl]methanesulphonamide (A-61603) was found to be 10- and 54-fold more potent than norepinephrine and phenylephrine, respectively. Brimonidine (UK 14304) evoked significantly smaller contractile responses than norepinephrine and phenylephrine, showing the presence of a small population of alpha2-adrenoceptors in these arteries, and this was confirmed by the studies with selective alpha1- and alpha2-adrenoceptor antagonists prazosin and (8aR,12aS,13aS)-5,8,8a,9,10,11,12,12a,13a-decahydro-3-methoxyl-12-(ethylsulphonyl)-6H-isoquino[2,1-g][1,6]-naphthyridine (RS 79948). Prazosin, 5-methyl-urapidil, and 2-[2,6-dimethoxyphenoxyethyl]aminomethyl)-1,4-benzodioxane (WB 4101) shifted the potency of norepinephrine concentration dependently giving pA2 values of 9.4, 8.9, and 10.1, respectively, showing the presence of the alpha1A-subtype in these arteries. Pretreatment with 1 and 10 microM chloroethylclonidine did not affect the potency of and maximum responses to norepinephrine, ruling out the presence of the alpha1B-subtype in these arteries. 8-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-8-azaspiro[4.5]decane-7,9-dione (BMY 7378, 10 and 100 nM) did not affect the potency of norepinephrine but a small shift was observed by 1 microM BMY 7378, giving a pK(B) value of 7.1, much less than that reported for the alpha1D-subtype. These results suggest the predominant involvement of alpha1A-adrenoceptor in the contractile responses to norepinephrine in these arteries. The physiological role of this subtype in the maintenance of peripheral arterial resistance is yet to be confirmed.

The alpha(1A)-adrenoceptor subtype mediates contraction in rat femoral resistance arteries

In this study, alpha(1)-adrenoceptor subtypes were characterised in rat femoral resistance arteries mounted on a small vessel myograph. A-61603 was found to be more potent than noradrenaline and phenylephrine in these arteries. Brimonidine (UK 14304) could not evoke any contractile responses and the sensitivity to noradrenaline and phenylephrine was not affected by (8aR,12aS,13aS)-5,8,8a,9,10,11,12,12a,13a-decahydro-3-methoxy-12-(ethylsulphonyl)-6H-isoquino[2,1-g][1,6]-naphthyridine (RS 79948), ruling out the presence of alpha(2)-adrenoceptors. Prazosin, 5-methyl-urapidil and 2-([2,6-dimethoxyphenoxyethyl]aminomethyl)-1,4-benzodioxane (WB 4101) produced rightward shifts in the sensitivity to noradrenaline, giving pA(2) values of 9.6, 9.4 and 10.4, respectively, in agreement with the presence of alpha(1A)-adrenoceptors. (8-[2-[4-(2-Methoxyphenyl)-1-piperazinyl]ethyl]-8-azaspiro[4.5]decane-7,9-dione (BMY 7378; 1 microM) produced a small shift in the sensitivity of noradrenaline giving a pK(B) of 7.2. In the presence of 300 nM 5-methyl-urapidil, sensitivity to noradrenaline was not further shifted by 1 microM BMY 7378. Responses to noradrenaline were unaffected by the alpha(1B)-adrenoceptor alkylating agent chloroethylclonidine (1 microM). These results suggest alpha(1A)-adrenoceptors mediate contractile responses to noradrenaline in rat femoral resistance arteries.

Increased alpha(1)- and alpha(2)-adrenoceptor-mediated contractile responses of human skeletal muscle resistance arteries in chronic limb ischemia

OBJECTIVE

Recently, we have shown augmented contractile responses of skeletal muscle resistance arteries to noradrenaline in patients with critical limb ischemia. We investigated whether this increased sensitivity in skeletal muscle resistance arteries is due to either alpha(1)- or alpha(2)-adrenoceptor-mediated responses or both.

METHODS

Skeletal muscle resistance arteries were isolated from the proximal (non-ischemic) and distal (ischemic) parts of limbs amputated for critical limb ischemia and mounted on a small vessel wire myograph. Cumulative concentration response curves of the vessel segments to noradrenaline, phenylephrine and brimonidine were obtained in the presence or the absence of the selective antagonists, prazosin and RS79948.

RESULTS

Noradrenaline and phenylephrine produced almost equal maximal contractile responses. Brimonidine responses were smaller and were almost abolished by 0.1 microM RS 79948 while those of phenylephrine and noradrenaline were not affected. Prazosin reduced the maximum responses to brimonidine, shifted the concentration response curves of noradrenaline and phenylephrine rightwards giving pK(B) values of 9.86 and 9.33, respectively. Maximum responses produced by all three agonists in distal vessels were significantly higher than those obtained in proximal vessels.

CONCLUSIONS

Noradrenaline contractile responses in skeletal muscle resistance arteries are predominantly mediated by alpha(1)-adrenoceptors. Both alpha(1)- and alpha(2)-adrenoceptor-mediated responses are increased in the arteries from ischemic regions that may aggravate the decreased blood flow to the limbs due to arterial occlusion.

Evidence for the differential sensitivity to hypoxia of basal and agonist-induced nitric oxide release

Rat pulmonary arterial rings (phenylephrine pre-contracted), were relaxed by carbachol or thapsigargin, or were contracted by Nomega-nitro-L-arginine methyl ester (L-NAME). Mild hypoxia (41 mm Hg) attenuated the carbachol-induced relaxation, whereas the relaxant and contractile effects produced by thapsigargin and L-NAME were unaffected. More severe hypoxia (20 mm Hg) abolished thapsigargin-induced relaxation, with no further change in responses to carbachol or L-NAME. At 7 mm Hg, carbachol-induced relaxation was completely inhibited, and the L-NAME-induced contraction was attenuated but not abolished. The present data is consistent with the conclusion that nitric oxide (NO) synthase activity is less susceptible to oxygen deprivation under basal conditions than during activation.