Tet2-mediated clonal hematopoiesis in nonconditioned mice accelerates age-associated cardiac dysfunction

Clonal hematopoiesis of indeterminate potential is prevalent in elderly individuals and associated with increased risks of all-cause mortality and cardiovascular disease. However, mouse models to study the dynamics of clonal hematopoiesis and its consequences on the cardiovascular system under homeostatic conditions are lacking. We developed a model of clonal hematopoiesis using adoptive transfer of unfractionated ten-eleven translocation 2-mutant (Tet2-mutant) bone marrow cells into nonirradiated mice. Consistent with age-related clonal hematopoiesis observed in humans, these mice displayed a progressive expansion of Tet2-deficient cells in multiple hematopoietic stem and progenitor cell fractions and blood cell lineages. The expansion of the Tet2-mutant fraction was also observed in bone marrow-derived CCR2+ myeloid cell populations within the heart, but there was a negligible impact on the yolk sac-derived CCR2- cardiac-resident macrophage population. Transcriptome profiling revealed an enhanced inflammatory signature in the donor-derived macrophages isolated from the heart. Mice receiving Tet2-deficient bone marrow cells spontaneously developed age-related cardiac dysfunction characterized by greater hypertrophy and fibrosis. Altogether, we show that Tet2-mediated hematopoiesis contributes to cardiac dysfunction in a nonconditioned setting that faithfully models human clonal hematopoiesis in unperturbed bone marrow. Our data support clinical findings that clonal hematopoiesis per se may contribute to diminished health span.

Acute and Chronic Increases of Circulating FSTL1 Normalize Energy Substrate Metabolism in Pacing-Induced Heart Failure

BACKGROUND

FSTL1 (follistatin-like protein 1) is an emerging cardiokine/myokine that is upregulated in heart failure (HF) and is found to be cardioprotective in animal models of cardiac injury. We tested the hypothesis that circulating FSTL1 can affect cardiac function and metabolism under baseline physiological conditions and in HF.

METHODS AND RESULTS

FSTL1 was acutely (10 minutes) or chronically (2 weeks) infused to attain clinically relevant blood levels in conscious dogs with cardiac tachypacing-induced HF. Dogs with no cardiac pacing and FSTL1 infusion served as control. ³H-oleate and ¹⁴C-glucose were infused to track the metabolic fate of free fatty acids and glucose. Cardiac uptake of lactate and ketone bodies and systemic respiratory quotient were also measured. HF caused a shift from prevalent cardiac and systemic fat to carbohydrate oxidation. Although acute FSTL1 administration caused minimal hemodynamic changes at baseline, in HF dogs it enhanced cardiac oxygen consumption and transiently reversed the changes in free fatty acid and glucose oxidation and systemic respiratory quotient. In HF, chronic FSTL1 infusion stably normalized cardiac free fatty acid, glucose, ketone body consumption, and systemic respiratory quotient, while moderately improving diastolic and contractile function. Consistently, FSTL1 prevented the downregulation of medium-chain acyl-CoA dehydrogenase-a representative enzyme of the free fatty acid oxidation pathway. Complementary in vitro experiments in primary cardiac and skeletal muscle myocytes showed that FSTL1 stimulated oxygen consumption through AMPK (AMP-activated kinase) activation.

CONCLUSIONS

These findings support a novel function for FSTL1 and provide the first direct evidence that a circulating cardiokine/myokine can alter myocardial and systemic energy substrate metabolism, in vivo.

Abstract 018: TET2 Loss of Function-driven Clonal Hematopoiesis Promotes Age-related Vascular and Systemic Inflammation and Metabolic Dysfunction in Mice

Background: Acquired mutations in the hematopoietic system and subsequent clonal hematopoiesis are emerging as potential new drivers of atherosclerotic cardiovascular disease. TET2 was the first gene reported to exhibit acquired mutations in blood cells of cancer-free elderly individuals and we recently reported that the clonal expansion of TET2-mutant hematopoietic cells accelerates atherogenesis in mouse models by exacerbating inflammatory responses in the atherosclerotic plaque. The objective of this study was to examine whether TET2 loss of function-driven clonal hematopoiesis also has systemic effects on age-related inflammation and metabolic function beyond its direct actions on the plaque.

Methods: An adoptive transfer technique was used to introduce a small percentage of Tet2-/- hematopoietic cells in non-irradiated C57Bl/6J mice, which were monitored for 16 months following transfer. Flow cytometry techniques were used to follow the expansion of Tet2-/- cells in the blood.

Results: Tet2-/- hematopoietic cells expanded progressively over time after adoptive transfer, with a mild myeloid bias. This was paralleled by increased expression of the pro-inflammatory cytokines IL-1β and IL-6 in the white adipose tissue and the aortic wall, as well as by increased serum levels of IL-6. Tet2-/- expansion also led to exacerbated systemic insulin resistance, as revealed by insulin tolerance tests.

Conclusion: TET2-deficient hematopoietic cell expansion promotes vascular and systemic inflammation, as well as metabolic dysfunction in aging mice. These results support a causal role for TET2 mutation-driven clonal hematopoiesis in age-related cardiometabolic disease, and suggest that somatic TET2 mutations may contribute to atherosclerosis by promoting inflammation both systemically and locally in the atherosclerotic plaque.

Genetic deficiency of Wnt5a diminishes disease severity in a murine model of rheumatoid arthritis

BACKGROUND

Rheumatoid arthritis (RA) is a common autoimmune disease characterized by chronic inflammation of the joints, leading to bone erosion and joint dysfunction. Despite the recent successes of disease-modifying anti-rheumatic drugs (DMARDs), there is still clinical need for understanding the development and molecular etiology of RA. Wnts are developmental morphogens whose roles in adult pathology are poorly characterized. Wnt5a is a member of the non-canonical family of Wnts that modulates a wide range of cell processes, including differentiation, migration, and inflammation. Wnt5a has been implicated as a possible contributor to arthritis and it is upregulated in synovial fibroblasts from RA patients.

METHODS

We investigated the role of endogenous Wnt5a in RA. Tamoxifen-inducible, Wnt5a knockout (Wnt5a cKO) mice and littermate controls were monitored for arthritis development and joint pathology using the K/BxN serum transfer-induced arthritis (STIA) model. To explore a role of Wnt5a in osteoclast fusion, bone marrow-derived monocytes (BMDMs) were differentiated in vitro.

RESULTS

Wnt5a cKO mice were resistant to arthritis development compared to control littermates as assessed by ankle thickness and histologic measurements. Some parameters of inflammation were reduced in the Wnt5a cKO mice, including the extent of polymononuclear cell infiltration and extra-articular inflammation. Wnt5a cKO mice also exhibited less cartilage destruction and a reduction in osteoclast activity with concomitant reduction in tartrate-resistant acid phosphatase (TRAP), cathepsin K (CTSK), macrophage colony-stimulating factor (MCSF), matrix metalloproteinase (MMP)2 and MMP9 in the arthritic joints. Treatment of BMDMs with Wnt5a enhanced osteoclast fusion and increased the expression of dendrocyte-expressed seven transmembrane protein (DCSTAMP) and MMP9, that are necessary for osteoclast formation and activity.

CONCLUSIONS

These data suggest that Wnt5a modulates the development of arthritis by promoting inflammation and osteoclast fusion, and provide the first mouse genetic evidence of a role for endogenous Wnt5a in autoimmune disease.

Humans and Mice Display Opposing Patterns of "Browning" Gene Expression in Visceral and Subcutaneous White Adipose Tissue Depots

Visceral adiposity is much more strongly associated with cardiometabolic disease in humans than subcutaneous adiposity. Browning, the appearance of brown-like adipocytes in the white adipose tissue (WAT), has been shown to protect mice against metabolic dysfunction, suggesting the possibility of new therapeutic approaches to treat obesity and type 2 diabetes. In mice, subcutaneous WAT depots express higher levels of browning genes when compared with visceral WAT, further suggesting that differences in WAT browning could contribute to the differences in the pathogenicity of the two depots. However, the expression of browning genes in different WAT depots of human has not been characterized. Here, it is shown that the expression of browning genes is higher in visceral than in subcutaneous WAT in humans, a pattern that is opposite to what is observed in mice. These results suggest that caution should be applied in extrapolating the results of murine browning gene expression studies to human pathophysiology.

Corrigendum: Ionizing Particle Radiation as a Modulator of Endogenous Bone Marrow Cell Reprogramming: Implications for Hematological Cancers

[This corrects the article on p. 231 in vol. 5, PMID: 26528440.].

Ionizing Particle Radiation as a Modulator of Endogenous Bone Marrow Cell Reprogramming: Implications for Hematological Cancers

Exposure of individuals to ionizing radiation (IR), as in the case of astronauts exploring space or radiotherapy cancer patients, increases their risk of developing secondary cancers and other health-related problems. Bone marrow (BM), the site in the body where hematopoietic stem cell (HSC) self-renewal and differentiation to mature blood cells occurs, is extremely sensitive to low-dose IR, including irradiation by high-charge and high-energy particles. Low-dose IR induces DNA damage and persistent oxidative stress in the BM hematopoietic cells. Inefficient DNA repair processes in HSC and early hematopoietic progenitors can lead to an accumulation of mutations whereas long-lasting oxidative stress can impair hematopoiesis itself, thereby causing long-term damage to hematopoietic cells in the BM niche. We report here that low-dose ¹H- and ⁵⁶Fe-IR significantly decreased the hematopoietic early and late multipotent progenitor (E- and L-MPP, respectively) cell numbers in mouse BM over a period of up to 10 months after exposure. Both ¹H- and ⁵⁶Fe-IR increased the expression of pluripotent stem cell markers Sox2, Nanog, and Oct4 in L-MPPs and 10 months post-IR exposure. We postulate that low doses of ¹H- and ⁵⁶Fe-IR may induce endogenous cellular reprogramming of BM hematopoietic progenitor cells to assume a more primitive pluripotent phenotype and that IR-induced oxidative DNA damage may lead to mutations in these BM progenitors. This could then be propagated to successive cell lineages. Persistent impairment of BM progenitor cell populations can disrupt hematopoietic homeostasis and lead to hematologic disorders, and these findings warrant further mechanistic studies into the effects of low-dose IR on the functional capacity of BM-derived hematopoietic cells including their self-renewal and pluripotency.

Abstract 134: Low Dose Particle Radiation Affects Long-Term Survival of Bone Marrow Progenitor Cell Populations

Radiation-induced decreases in the number of bone marrow (BM)-derived endothelial progenitor cell (BM-EPCs) and their lineage precursors which include Early- and Late-Multi-Potent Progenitor cells (E-MPP and L-MPP) could contribute to the pathogenesis of ischemic and vascular diseases. We examined the effect of full-body single dose of proton (1H) at 0.5 Gy, 1 GeV and 0.15 Gy, 1 GeV/nucleon of iron (56Fe) - ionizing radiation (IR) on survival and proliferation of BM-EPCs. The survival of E-MPPs and L-MPPs in the BM after particle IR in C57BL/6 mice were determined at 1, 2, 4, 8, 12, 28 and 40 weeks post-IR. BM-derived mononuclear cells were triple-stained with RAM34 (CD34, c-kit, and Sca1), AC133, and hematopoietic lineage negative cocktail, then sorted by FASC for E- and L-MPP. BM EPCs ex-vivo - There was a transient 2.5-3.5-fold increase in BM-EPC apoptosis, with 3.5-fold increases for 56Fe and 1H at 5hrs and 24hrs, respectively that was no longer detected by day 7. Subsequently, there was a 3-fold increase in BM-EPC apoptosis on day 28 for both ion-IR mice. Compared to 24 hrs, there was a ~20% (1H) and ~45% (56Fe) increase in the rate of EPC proliferation on day 14 that returned to control levels on day 28. BM E-MPP and L-MPP in vivo - Compared to control mice, 1H-IR increased the number of both E-MPPs (665%) and L-MPPs (203%), whereas 56Fe-IR decreased E-MPP (74%) and L-MPPs (65%) at 1 week post-IR, suggesting stimulation by 1H but overt damage by 56Fe in the BM milieu. In 56Fe-IR mice, E-MPPs recovered between 4 and 12 weeks, followed by declines at later time points. In 1H-IR mice, E-MPPs were near control levels up to 4 weeks, but declined at later time points. The long-lasting and cyclical effects of IR on the BM E- and L-MPPs after a single 1H or 56Fe IR dose suggests the presence of prolonged and non-targeted effects in BM milieu, that occur in cells that were not traversed by IR, rather induced by signals from IR cells. Our studies showed that, both 1H- and 56Fe-IR has profound and long-lasting (28-40 months) negative effects on the number of E- and L-MPPs. Future longitudinal studies are necessary to determine whether BM progenitor cells may be affected after terrestrial IR exposure, such as cancer radiotherapy, CT and PET scans, and in astronauts after exploration-type space missions.

Abstract 290: Noncanonical Wnt Signaling Contributes to Angiotensin II-Induced Vascular Inflammation and Abdominal Aortic Aneurysm Formation

Background: Abdominal aortic aneurysms (AAA) are life-threatening localized dilations of the abdominal aorta. A precise knowledge of the molecular mechanisms underlying this disease is required, especially because there are no validated drugs for its treatment. Wnt proteins are secreted signaling molecules that play fundamental roles during embryo development and in the adult. There are 19 Wnt family members in mammals, which frequently have overlapping or redundant functions. Wnt5a is a particularly unique Wnt protein that induces non-canonical Wnt signaling and appears to modulate innate immunity and several signaling pathways involved in vascular inflammation. However, its role in the development of macrovascular pathologies remains unexplored. HYPOTHESIS. Wnt5a-mediated non-canonical Wnt signaling contributes to vascular inflammation and AAA development.

METHODS: Cre-loxP strategies were used to generate whole-body Wnt5a-deficient mice, myeloid- Wnt5a-deficient mice and myeloid Wnt5a-overexpressing mice. AAAs were induced in these mouse strains in an apolipoprotein E deficient (apoE-KO) or wild-type (apoE-WT) background by Angiotensin II (Ang II) infusion. Ultrasonography was used to evaluate AAA progression. AAA samples were harvested for histology and gene expression analysis. RESULTS. Whole-body ablation of Wnt5a inhibited Ang II-induced vascular inflammation and AAA formation in apoE-KO mice. Myeloid-specific Wnt5a ablation reduced AAA size, incidence rate and severity, suggesting that myeloid cells are a significant source of pathogenic Wnt5a. Conversely, myeloid-restricted Wnt5a-overexpression led to rapid formation and rupture of dissecting AAAs in Ang II-infused apoE-KO and apoE-WT mice. In human AAAs, Wnt5a expression is significantly increased both at the transcript and protein levels. Mechanistically, Wnt5a appears to promote AAA formation at least in part by promoting vascular inflammation and extracellular matrix remodeling via augmented recruitment of immune cells to the vessel wall.

CONCLUSION: Wnt5a-mediated non-canonical Wnt signaling plays a major role in inflammatory AAA formation and may be a potential target for novel AAA therapies.

Divergent roles for adiponectin receptor 1 (AdipoR1) and AdipoR2 in mediating revascularization and metabolic dysfunction in vivo

Adiponectin is a well described anti-inflammatory adipokine that is highly abundant in serum. Previous reports have found that adiponectin deficiency promotes cardiovascular and metabolic dysfunction in murine models, whereas its overexpression is protective. Two candidate adiponectin receptors, AdipoR1 and AdipoR2, are uncharacterized with regard to cardiovascular tissue homeostasis, and their in vivo metabolic functions remain controversial. Here we subjected AdipoR1- and AdipoR2-deficient mice to chronic hind limb ischemic surgery. Blood flow recovery in AdipoR1-deficient mice was similar to wild-type; however, revascularization in AdipoR2-deficient mice was severely attenuated. Treatment with adiponectin enhanced the recovery of wild-type mice but failed to rescue the impairment observed in AdipoR2-deficient mice. In view of this divergent receptor function in the hind limb ischemia model, AdipoR1- and AdipoR2-deficient mice were also evaluated in a model of diet-induced obesity. Strikingly, AdipoR1-deficient mice developed severe metabolic dysfunction compared with wild type, whereas AdipoR2-deficient mice were protected from diet-induced weight gain and metabolic perturbations. These data show that AdipoR2, but not AdipoR1, is functionally important in an in vivo model of ischemia-induced revascularization and that its expression is essential for the revascularization actions of adiponectin. These data also show that, in contrast to revascularization responses, AdipoR1, but not AdipoR2 deficiency, leads to diet-induced metabolic dysfunction, revealing that these receptors have highly divergent roles in vascular and metabolic homeostasis.

Cyclooxygenase inhibition improves endothelial vasomotor dysfunction of visceral adipose arterioles in human obesity

OBJECTIVE

The purpose of this study was to determine whether cyclooxygenase inhibition improves vascular dysfunction of adipose microvessels from obese humans.

DESIGN AND METHODS

In 20 obese subjects (age 37 ± 12 years, BMI 47 ± 8 kg/m²), subcutaneous and visceral fat were collected during bariatric surgery and characterized for adipose depot-specific gene expression, endothelial cell phenotype, and microvascular function. Vasomotor function was assessed in response to endothelium-dependent agonists using videomicroscopy of small arterioles from fat.

RESULTS

Arterioles from visceral fat exhibited impaired endothelium-dependent, acetylcholine-mediated vasodilation, compared to the subcutaneous depot (P < 0.001). Expression of mRNA transcripts relevant to the cyclooxygenase pathway was upregulated in visceral compared to subcutaneous fat. Pharmacological inhibition of cyclooxygenase with indomethacin improved endothelium-dependent vasodilator function of arterioles from visceral fat by twofold (P = 0.01), whereas indomethacin had no effect in the subcutaneous depot. Indomethacin increased activation via serine-1177 phosphorylation of endothelial nitric oxide synthase in response to acetylcholine in endothelial cells from visceral fat. Inhibition of endothelial nitric oxide synthase with N(ω)-nitro-L-arginine methyl ester abrogated the effects of cyclooxygenase-inhibition suggesting that vascular actions of indomethacin were related to increased nitric oxide bioavailability.

CONCLUSIONS

Our findings suggest that cyclooxygenase-mediated vasoconstrictor prostanoids partly contribute to endothelial dysfunction of visceral adipose arterioles in human obesity.