Growth arrest specific protein 6 participates in DOCA-induced target-organ damage

Role of emerging vitamin K‑dependent proteins: Growth arrest‑specific protein 6, Gla‑rich protein and periostin (Review)

Vitamin K‑dependent proteins (VKDPs) are a group of proteins that need vitamin K to conduct carboxylation. Thus far, scholars have identified a total of 17 VKDPs in the human body. In this review, we summarize three important emerging VKDPs: Growth arrest‑specific protein 6 (Gas 6), Gla‑rich protein (GRP) and periostin in terms of their functions in physiological and pathological conditions. As examples, carboxylated Gas 6 and GRP effectively protect blood vessels from calcification, Gas 6 protects from acute kidney injury and is involved in chronic kidney disease, GRP contributes to bone homeostasis and delays the progression of osteoarthritis, and periostin is involved in all phases of fracture healing and assists myocardial regeneration in the early stages of myocardial infarction. However, periostin participates in the progression of cardiac fibrosis, idiopathic pulmonary fibrosis and airway remodeling of asthma. In addition, we discuss the relationship between vitamin K, VKDPs and cancer, and particularly the carboxylation state of VKDPs in cancer.

Innate Immune Cells Are Regulated by Axl in Hypertensive Kidney

The balance between adaptive and innate immunity in kidney damage in salt-dependent hypertension is unclear. We investigated early renal dysfunction and the influence of Axl, a receptor tyrosine kinase, on innate immune response in hypertensive kidney in mice with lymphocyte deficiency (Rag1^-/-). The data suggest that increased presence of CD11b⁺ myeloid cells in the medulla might explain intensified salt and water retention as well as initial hypertensive response in Rag1^-/- mice. Global deletion of Axl on Rag1^-/- background reversed kidney dysfunction and accumulation of myeloid cells in the kidney medulla. Chimeric mice that lack Axl in innate immune cells (in the absence of lymphocytes) significantly improved kidney function and abolished early hypertensive response. The bioinformatics analyses of Axl-related gene-gene interaction networks established tissue-specific variation in regulatory pathways. It was confirmed that complement C3 is important for Axl-mediated interactions between myeloid and vascular cells in hypertensive kidney. In summary, innate immunity is crucial for renal dysfunction in early hypertension, and is highly influenced by the presence of Axl.

Vitamin K Dependent Proteins in Kidney Disease

Patients with chronic kidney disease (CKD) have an increased risk of developing vascular calcifications, as well as bone dynamics impairment, leading to a poor quality of life and increased mortality. Certain vitamin K dependent proteins (VKDPs) act mainly as calcification inhibitors, but their involvement in the onset and progression of CKD are not completely elucidated. This review is an update of the current state of knowledge about the relationship between CKD and four extrahepatic VKDPs: matrix Gla protein, osteocalcin, growth-arrest specific protein 6 and Gla-rich protein. Based on published literature in the last ten years, the purpose of this review is to address fundamental aspects about the link between CKD and circulating VKDPs levels as well as to raise new topics about how the interplay between molecular weight and charge could influence the modifications of circulating VKDPs at the glomerular level, or whether distinct renal etiologies have effect on VKDPs. This review is the output of a systematic literature search and may open future research avenues in this niche domain.

Vitamin K‑dependent proteins involved in bone and cardiovascular health (Review)

In postmenopausal women and elderly men, bone density decreases with age and vascular calcification is aggravated. This condition is closely associated with vitamin K2 deficiency. A total of 17 different vitamin K-dependent proteins have been identified to date. Vitamin K-dependent proteins are located within the bone, heart and blood vessels. For instance, carboxylated osteocalcin is beneficial for bone and aids the deposition of calcium into the bone matrix. Carboxylated matrix Gla protein effectively protects blood vessels and may prevent calcification within the vascular wall. Furthermore, carboxylated Gla-rich protein has been reported to act as an inhibitor in the calcification of the cardiovascular system, while growth arrest-specific protein-6 protects endothelial cells and vascular smooth muscle cells, resists apoptosis and inhibits the calcification of blood vessels by inhibiting the apoptosis of vascular smooth muscle cells. In addition, periostin may promote the differentiation, aggregation, adhesion and proliferation of osteoblasts. Periostin also occurs in the heart and may be associated with the reconstruction of heart function. These vitamin K-dependent proteins may exert their functions following γ-carboxylation with vitamin K, and different vitamin K-dependent proteins may exhibit synergistic effects or antagonistic effects on each other. In the cardiovascular system with vitamin K antagonist supplement or vitamin K deficiency, calcification occurs in the endothelium of blood vessels and vascular smooth muscle cells are transformed into osteoblast-like cells, a phenomenon that resembles bone growth. Both the bone and cardiovascular system are closely associated during embryonic development. Thus, the present study hypothesized that embryonic developmental position and tissue calcification may have a certain association for the bone and the cardiovascular system. This review describes and briefly discusses several important vitamin K-dependent proteins that serve an important role in bone and the cardiovascular system. The results of the review suggest that the vascular calcification and osteogenic differentiation of vascular smooth muscle cells may be associated with the location of the bone and cardiovascular system during embryonic development.

Vaccarin alleviates hypertension and nephropathy in renovascular hypertensive rats

The kidney is an important organ in the regulation of blood pressure, and it is also one of the primary target organs of hypertension. Kidney damage in response to hypertension eventually leads to renal insufficiency. The authors previously demonstrated that vaccarin exhibits a protective role in endothelial injury. However, the effects of vaccarin on the two-kidney, one clip (2K1C) renovascular hypertension model and subsequent kidney injury have yet to be fully elucidated. The present study was designed to investigate the roles and mechanisms of vaccarin in attenuating hypertension and whether vaccarin had beneficial effects on kidney injury. The 2K1C rats had greater fibrosis, apoptosis, reactive oxygen species production, inflammation, angiotensin II (Ang II) and angiotensin type 1 (AT1) receptors in the right kidney compared with normotensive rats, which were alleviated by a high dose of vaccarin and captopril. Vaccarin treatment attenuated hypertension, reduced fibrosis markers, NADPH oxidase (NOX)-2, NOX-4, 3-nitrotyrosine, tumor necrosis factor-α, interleukin 1β (IL-1β), and IL-6 protein levels and altered pro-apoptotic protein levels including caspase-3, anti-apoptosis protein B cell lymphoma (Bcl)-2 and Bcl-2 associated X, apoptosis regulator in the right kidney of 2K1C rats. These findings suggest that the protective effects of vaccarin on the right kidney in renovascular hypertension are possibly due to downregulation of fibrosis, inflammatory molecules, oxidative stress, Ang II, and AT1 receptor levels.

Hyperaldosteronism induces left atrial systolic and diastolic dysfunction

Patients with hypertension and hyperaldosteronism show an increased risk of stroke compared with patients with essential hypertension. Aim of the study was to assess the effects of aldosterone on left atrial function in rats as a potential contributor to thromboembolism. Osmotic mini-pumps delivering 1.5 μg aldosterone/h were implanted in rats subcutaneously (Aldo, n = 39; controls, n = 38). After 8 wk, left ventricular pressure-volume analysis of isolated working hearts was performed, and left atrial systolic and diastolic function was also assessed by atrial pressure-diameter loops. Moreover, left atrial myocytes were isolated to investigate their global and local Ca2+ handling and contractility. At similar heart rates, pressure-volume analysis of isolated hearts and in vivo hemodynamic measurements revealed neither systolic nor diastolic left ventricular dysfunction in Aldo. In particular, atrial filling pressures and atrial size were not increased in Aldo. Aldo rats showed a significant reduction of atrial late diastolic A wave, atrial active work index, and increased V waves. Consistently, in Aldo rats, sarcomere shortening and the amplitude of electrically evoked global Ca2+ transients were substantially reduced. Sarcoplasmic reticulum-Ca2+ content and fractional Ca2+ release were decreased, substantiated by a reduced sarcoplasmic reticulum calcium ATPase activity, resulting from a reduced CAMKII-evoked phosphorylation of phospholamban. Hyperaldosteronism induced atrial systolic and diastolic dysfunction, while atrial size and left ventricular hemodynamics, including filling pressures, were unaffected in rats. The described model suggests a direct causal link between hyperaldosteronism and decreased atrial contractility and diastolic compliance.

Role of Axl in T-Lymphocyte Survival in Salt-Dependent Hypertension

OBJECTIVE

Survival of immune and nonimmune cells relies on Axl, a receptor tyrosine kinase, which is implicated in hypertension. Activated T lymphocytes are involved in regulation of high blood pressure. The goal of the study was to investigate the role of Axl in T-lymphocyte functions and its contribution to salt-dependent hypertension.

APPROACH AND RESULTS

We report increased apoptosis in peripheral blood from Axl(-/-) mice because of lower numbers of white blood cells mostly lymphocytes. In vitro studies showed modest reduction in interferon gamma production in Axl(-/-) type 1 T helper cells. Axl did not affect basic proliferation capacity or production of interleukin 4 in Axl(-/-) type 2 T helper cells. However, competitive repopulation of Axl(-/-) bone marrow or adoptive transfer of Axl(-/-) CD4(+) T cells to Rag1(-/-) mice showed robust effect of Axl on T lymphocyte expansion in vivo. Adoptive transfer of Axl(-/-) CD4(+) T cells was protective in a later phase of deoxycorticosterone-acetate and salt hypertension. Reduced numbers of CD4(+) T cells in circulation and in perivascular adventitia decreased vascular remodeling and increased vascular apoptosis in the late phase of hypertension.

CONCLUSIONS

These findings suggest that Axl is critical for survival of T lymphocytes, especially during vascular remodeling in hypertension.

Growth Arrest-Specific 6 Exacerbates Pressure Overload-Induced Cardiac Hypertrophy

Growth arrest-specific 6 (GAS6) is a member of the vitamin K-dependent protein family that is involved in the regulation of the cardiovascular system, including vascular remodeling, homeostasis, and atherosclerosis. However, there is still no study that systemically elucidates the role of GAS6 in cardiac hypertrophy. Here, we found that GAS6 was upregulated in human dilated cardiomyopathic hearts, hypertrophic murine hearts, and angiotensin II-treated cardiomyocytes. Next, we examined the influence of GAS6 expression in response to a cardiac stress by inducing chronic pressure overload with aortic banding in wild-type and GAS6-knockout mice or cardiac-specific GAS6 overexpressing mice. Under basal conditions, the GAS6-knockout mice had normal left ventricular structure and function but after aortic banding, the mice demonstrated less hypertrophy, fibrosis, and contractile dysfunction when compared with wild-type mice. Conversely, cardiac-specific overexpression of GAS6 exacerbated aortic banding-induced cardiac hypertrophy, fibrosis, and dysfunction. Furthermore, we demonstrated that GAS6 activated the mitogen-activated protein kinase kinase 1/2-extracellular signal-regulated kinase 1/2 pathway during pressure overload-induced cardiac hypertrophy, and the pharmacological mitogen-activated protein kinase kinase 1/2 inhibitor U0126 almost completely reversed GAS6 overexpression-induced cardiac hypertrophy and fibrosis, resulting in improved cardiac function. Collectively, our data support the notion that GAS6 impairs ventricular adaptation to chronic pressure overload by activating mitogen-activated protein kinase kinase 1/2-extracellular signal-regulated kinase 1/2 signaling. Our findings suggest that strategies to reduce GAS6 activity in cardiac tissue may be a novel approach to attenuate the development of congestive heart failure.

Postmortem serum protein growth arrest-specific 6 levels in sepsis-related deaths

Growth arrest-specific 6 (Gas6) is widely expressed in leukocytes, platelets, endothelial cells, and monocytes. It regulates various processes including granulocyte adhesion to the endothelium, cell migration, thrombus stabilization, and cytokine release. In humans, increased plasma Gas6 levels have been described in patients with sepsis and septic shock. In this study, Gas6 concentrations were measured in postmortem serum from femoral blood in a series of sepsis-related fatalities and control cases. The aims were twofold: first, to determine whether Gas6 can be reliably determined in postmortem serum; and second, to assess its diagnostic potential in identifying sepsis-related deaths. Two study groups were prospectively formed, a sepsis-related fatalities group (24 cases) and a control group (24 cases) including cases of deep vein thrombosis and fatal pulmonary embolism, cases of systemic inflammatory response syndrome in severe trauma, cases of end-stage renal failure, and cases of hanging (non-septic, non-SIRS, non-end stage renal failure cases). The preliminary results of this study seem to indicate that Gas6 can be effectively measured in postmortem serum. However, Gas6 levels in sepsis-related fatalities do not appear to be clearly distinguishable from concentrations in pulmonary embolism, severe trauma, and end-stage renal failure cases. These findings tend to support previous reports that indicated that Gas6 behaves as an acute phase reactant and can be considered a general marker of inflammation rather than a specific biomarker of sepsis.

Pharmacological inhibition of galectin-3 protects against hypertensive nephropathy

Galectin-3 activation is involved in the pathogenesis of renal damage and fibrogenesis. Limited data are available to suggest that galectin-3-targeted intervention is a potential therapeutic candidate for the prevention of chronic kidney disease. Homozygous TGR(mREN)27 (REN2) rats develop severe high blood pressure (BP) and hypertensive end-organ damage, including nephropathy and heart failure. Male REN2 rats were treated with N-acetyllactosamine [galectin-3 inhibitor (Gal3i)] for 6 wk; untreated REN2 and Sprague-Dawley rats served as controls. We measured cardiac function with echocardiogram and invasive hemodynamics before termination. BP and proteinuria were measured at baseline and at 3 and 6 wk. Plasma creatinine was determined at 6 wk. Renal damage was assessed for focal glomerular sclerosis, glomerular desmin expression, glomerular and interstitial macrophages, kidney injury molecule-1 expression, and α-smooth muscle actin expression. Inflammatory cytokines and extracellular matrix proteinases were quantified by quantitative real-time PCR. Systolic BP was higher in control REN2 rats, with no effect of Gal3i treatment. Plasma creatinine and proteinuria were significantly increased in control REN2 rats; Gal3i treatment reduced both. Renal damage (focal glomerular sclerosis, desmin, interstitial macrophages, kidney injury molecule-1, α-smooth muscle actin, collagen type I, and collagen type III) was also improved by Gal3i. All inflammatory markers (CD68, IL-68, galectin-3, and monocyte chemoattractant protein-1) were elevated in control REN2 rats and attenuated by Gal3i. Markers of extracellular matrix turnover were marginally altered in untreated REN2 rats compared with Sprague-Dawley rats. In conclusion, galectin-3 inhibition attenuated hypertensive nephropathy, as indicated by reduced proteinuria, improved renal function, and decreased renal damage. Drugs binding to galectin-3 may be therapeutic candidates for the prevention of chronic kidney disease.

Role of Axl in early kidney inflammation and progression of salt-dependent hypertension

The Gas6/Axl pathway regulates many cell functions and is implicated in hypertension. In this study, we aimed to investigate the role of Axl in immune cells on initiation and progression of salt-dependent hypertension. Deoxycorticosterone acetate (75 mg/60 days release)-salt hypertension was induced for 1 week or 6 weeks in Axl chimeras generated by bone marrow transplant to restrict Axl deficiency to hematopoietic or nonhematopoietic compartments. Depletion of Axl in hematopoietic cells (Axl(-/-) →Axl(+/+)) reduced (133 ± 2 mm Hg) increase in systolic blood pressure compared with other Axl chimeras (≈150 mm Hg) 1 week after deoxycorticosterone acetate-salt. Urine protein and renal oxidative stress were lowest in Axl(-/-) →Axl(+/+) at 1 week after deoxycorticosterone acetate-salt. Compensatory increase in Gas6 in kidneys of recipient Axl(-/-) may affect kidney function and blood pressure in early phase of hypertension. Flow cytometry on kidneys from Axl(-/-) →Axl(+/+) showed increase in total leukocytes, B, and dendritic cells and decrease in macrophages compared with Axl(+/+) →Axl(+/+). These immune changes were associated with decrease in proinflammatory gene expression, in particular interferon γ. Systolic blood pressure returned to baseline in Axl(-/-) →Axl(+/+) and Axl(-/-) →Axl(-/-) but remained increased in Axl(+/+) →Axl(+/+) and Axl(+/+) →Axl(-/-) chimeras after 6 weeks of deoxycorticosterone acetate-salt. Vascular apoptosis was increased in the global Axl(-/-) chimeras in the late phase of hypertension. In summary, we found that expression of Axl in hematopoietic cells is critical for kidney pathology in early phase of salt-dependent hypertension. However, Axl in both hematopoietic and nonhematopoietic lineages contributes to the late phase of hypertension.

OPN deficiency results in severe glomerulosclerosis in uninephrectomized mice

Osteopontin (OPN) expression has been reported to be elevated in experimental models of renal injury such as arterial hypertension or diabetic nephropathy finally leading to focal segmental glomerulosclerosis (FSGS). FSGS is characterized by glomerular matrix deposition and loss or damage of podocytes that represent the main constituents of the glomerular filtration barrier. To evaluate the role of OPN in the kidney we investigated WT and OPN knockout mice (OPN-/-) without treatment, after uninephrectomy (UNX), as well as after UNX and desoxycorticosterone acetate (DOCA)-salt treatment with respect to urine parameters, glomerular morphology, and expression of podocyte markers. OPN-/- mice showed normal urine parameters while a thickening of the glomerular basement membrane was evident. Intriguingly, following UNX, OPN-/- mice exhibited prominent FSGS, proteinuria, and glomerular matrix deposition. Electron microscopy revealed bulgings of the glomerular basement membrane and occasionally an effacement of podocytes. After UNX and DOCA-salt treatment, severe glomerular lesions as well as proteinuria and albuminuria were seen in WT and OPN-/- mice. Moreover, we found a reduction of specific markers such as Wilm's tumor-1, podocin, and synaptopodin in both experimental groups indicating a loss of podocytes. Podocyte damage was accompanied by increased number of Ki-67-positive cells in the parietal epithelium of Bowman's capsule. We conclude that OPN plays a crucial role in adaptation of podocytes following renal ablation and is renoprotective when glomerular mechanical load is increased.

Placental growth factor mediates aldosterone-dependent vascular injury in mice

In clinical trials, aldosterone antagonists reduce cardiovascular ischemia and mortality by unknown mechanisms. Aldosterone is a steroid hormone that signals through renal mineralocorticoid receptors (MRs) to regulate blood pressure. MRs are expressed and regulate gene transcription in human vascular cells, suggesting that aldosterone might have direct vascular effects. Using gene expression profiling, we identify the pro-proliferative VEGF family member placental growth factor (PGF) as an aldosterone-regulated vascular MR target gene in mice and humans. Aldosterone-activated vascular MR stimulated Pgf gene transcription and increased PGF protein expression and secretion in the mouse vasculature. In mouse vessels with endothelial damage and human vessels from patients with atherosclerosis, aldosterone enhanced expression of PGF and its receptor, FMS-like tyrosine kinase 1 (Flt1). In atherosclerotic human vessels, MR antagonists inhibited PGF expression. In vivo, aldosterone infusion augmented vascular remodeling in mouse carotids following wire injury, an effect that was lost in Pgf-/- mice. In summary, we have identified PGF as what we believe to be a novel downstream target of vascular MR that mediates aldosterone augmentation of vascular injury. These findings suggest a non-renal mechanism for the vascular protective effects of aldosterone antagonists in humans and support targeting the vascular aldosterone/MR/PGF/Flt1 pathway as a therapeutic strategy for ischemic cardiovascular disease.