Clemens Duerrschmid

TNF receptor 1 signaling is critically involved in mediating angiotensin-II-induced cardiac fibrosis

Angiotensin-II (Ang-II) is associated with many conditions involving heart failure and pathologic hypertrophy. Ang-II induces the synthesis of monocyte chemoattractant protein-1 that mediates the uptake of CD34(+)CD45(+) monocytic cells into the heart. These precursor cells differentiate into collagen-producing fibroblasts and are responsible for the Ang-II-induced development of non-adaptive cardiac fibrosis. In this study, we demonstrate that in vitro, using a human monocyte-to-fibroblast differentiation model, Ang-II required the presence of tumor necrosis factor-alpha (TNF) to induce fibroblast maturation from monocytes. In vivo, mice deficient in both TNF receptors did not develop cardiac fibrosis in response to 1week Ang-II infusion. We then subjected mice deficient in either TNF receptor 1 (TNFR1-KO) or TNF receptor 2 (TNFR2-KO) to continuous Ang-II infusion. Compared to wild-type, in TNFR1-KO, but not in TNFR2-KO hearts, collagen deposition was greatly attenuated, and markedly fewer CD34(+)CD45(+) cells were present. Quantitative RT-PCR demonstrated a striking reduction of key fibrosis-related, as well as inflammation-related mRNA expression in Ang-II-treated TNFR1-KO hearts. TNFR1-KO animals also developed less cardiac remodeling, cardiac hypertrophy, and hypertension compared to wild-type and TNFR2-KO in response to Ang-II. Our data suggest that TNF induced Ang-II-dependent cardiac fibrosis by signaling through TNFR1, which enhances the generation of monocytic fibroblast precursors in the heart.

Th1/M1 Conversion to Th2/M2 Responses in Models of Inflammation Lacking Cell Death Stimulates Maturation of Monocyte Precursors to Fibroblasts

We have demonstrated that cardiac fibrosis arises from the differentiation of monocyte-derived fibroblasts. We present here evidence that this process requires sequential Th1 and Th2 induction promoting analogous M1 (classically activated) and M2 (alternatively activated) macrophage polarity. Our models are: (1) mice subjected to daily repetitive ischemia and reperfusion (I/R) without infarction and (2) the in vitro transmigration of human mononuclear leukocytes through human cardiac microvascular endothelium. In the mouse heart, leukocytes entered after I/R in response to monocyte chemoattractant protein-1 (MCP-1), which is the major cytokine induced by this protocol. Monocytes within the heart then differentiated into fibroblasts making collagen while bearing the markers of M2 macrophages. T cells were seen in these hearts as well as in the human heart with cardiomyopathy. In the in vitro model, transmigration of the leukocytes was likewise induced by MCP-1 and some monocytes matured into fibroblasts bearing M2 markers. In this model, the MCP-1 stimulus induced a transient Th1 and M1 response that developed into a predominantly Th2 and M2 response. An increase in the Th2 product IL-13 was present in both the human and the mouse models, consistent with its known role in fibrosis. In these simplified models, in which there is no cell death to stimulate an anti-inflammatory response, there is nonetheless a resolution of inflammation enabling a profibrotic environment. This induces the maturation of monocyte precursors into fibroblasts.

Tumor Necrosis Factor: A Mechanistic Link between Angiotensin-II-Induced Cardiac Inflammation and Fibrosis

Background—Continuous angiotensin-II infusion induced the uptake of monocytic fibroblast precursors that initiated the development of cardiac fibrosis; these cells and concurrent fibrosis were absent in mice lacking tumor necrosis factor receptor 1 (TNFR1). We now investigated their cellular origin and temporal uptake and the involvement of TNFR1 in monocyte-to-fibroblast differentiation. Methods and Results—Within a day, angiotensin-II induced a proinflammatory environment characterized by production of inflammatory chemokines, cytokines, and TH1-interleukins and uptake of bone marrow-derived M1 cells. After a week, the cardiac environment changed to profibrotic with growth factor and TH2-interleukin synthesis, uptake of bone marrow–derived M2 cells, and the presence of M2-related fibroblasts. TNFR1 signaling was not necessary for early M1 uptake, but its absence diminished the amount of M2 cells. TNFR1-knockout hearts also showed reduced levels of cytokine expression, but not of TH-related lymphokines. Reconstitution of wild-type bone marrow into TNFR1-knockout mice was sufficient to restore M2 uptake, upregulation of proinflammatory and profibrotic genes, and development of fibrosis in response to angiotensin-II. We also developed an in vitro mouse monocyte-to-fibroblast maturation assay that confirmed the essential role of TNFR1 in the sequential progression of monocyte activation and fibroblast formation. Conclusions—Development of cardiac fibrosis in response to angiotensin-II was mediated by myeloid precursors and consisted of 2 stages. A primary M1 inflammatory response was followed by a subsequent M2 fibrotic response. Although the first phase seemed to be independent of TNFR1 signaling, the later phase (and development of fibrosis) was abrogated by deletion of TNFR1.Background— Continuous angiotensin-II infusion induced the uptake of monocytic fibroblast precursors that initiated the development of cardiac fibrosis; these cells and concurrent fibrosis were absent in mice lacking tumor necrosis factor receptor 1 (TNFR1). We now investigated their cellular origin and temporal uptake and the involvement of TNFR1 in monocyte-to-fibroblast differentiation. Methods and Results— Within a day, angiotensin-II induced a proinflammatory environment characterized by production of inflammatory chemokines, cytokines, and TH1-interleukins and uptake of bone marrow-derived M1 cells. After a week, the cardiac environment changed to profibrotic with growth factor and TH2-interleukin synthesis, uptake of bone marrow–derived M2 cells, and the presence of M2-related fibroblasts. TNFR1 signaling was not necessary for early M1 uptake, but its absence diminished the amount of M2 cells. TNFR1-knockout hearts also showed reduced levels of cytokine expression, but not of TH-related lymphokines. Reconstitution of wild-type bone marrow into TNFR1-knockout mice was sufficient to restore M2 uptake, upregulation of proinflammatory and profibrotic genes, and development of fibrosis in response to angiotensin-II. We also developed an in vitro mouse monocyte-to-fibroblast maturation assay that confirmed the essential role of TNFR1 in the sequential progression of monocyte activation and fibroblast formation. Conclusions— Development of cardiac fibrosis in response to angiotensin-II was mediated by myeloid precursors and consisted of 2 stages. A primary M1 inflammatory response was followed by a subsequent M2 fibrotic response. Although the first phase seemed to be independent of TNFR1 signaling, the later phase (and development of fibrosis) was abrogated by deletion of TNFR1.

Asprosin is a centrally acting orexigenic hormone

Asprosin is a recently discovered fasting-induced hormone that promotes hepatic glucose production. Here we demonstrate that asprosin in the circulation crosses the blood–brain barrier and directly activates orexigenic AgRP+ neurons via a cAMP-dependent pathway. This signaling results in inhibition of downstream anorexigenic proopiomelanocortin (POMC)-positive neurons in a GABA-dependent manner, which then leads to appetite stimulation and a drive to accumulate adiposity and body weight. In humans, a genetic deficiency in asprosin causes a syndrome characterized by low appetite and extreme leanness; this is phenocopied by mice carrying similar mutations and can be fully rescued by asprosin. Furthermore, we found that obese humans and mice had pathologically elevated concentrations of circulating asprosin, and neutralization of asprosin in the blood with a monoclonal antibody reduced appetite and body weight in obese mice, in addition to improving their glycemic profile. Thus, in addition to performing a glucogenic function, asprosin is a centrally acting orexigenic hormone that is a potential therapeutic target in the treatment of both obesity and diabetes.

TNF/Ang‐II synergy is obligate for fibroinflammatory pathology, but not for changes in cardiorenal function

Angiotensin‐II (Ang‐II) infusion is associated with the development of interstitial fibrosis in both heart and kidney as a result of chemokine‐dependent uptake of monocytes and subsequent development of myeloid fibroblasts. This study emphasizes on the synergistic role of tumor necrosis factor (TNF) on the time course of Ang‐II‐induced fibrosis and inflammation in heart and kidney. In wild‐type (WT) hearts, Ang‐II‐induced fibrosis peaked within 1 week of infusion and remained stable over a 6‐week period, while the myeloid fibroblasts disappeared; TNF receptor‐1‐knockout (TNFR1‐KO) hearts did not develop a myeloid response or cardiac fibrosis during this time. WT hearts developed more accelerated cardiac hypertrophy and remodeling than TNFR1‐KO. In the kidney, 1‐week Ang‐II infusion did not evoke a fibrotic response; however, after 6 weeks, WT kidneys displayed modest but significant tubulointerstitial collagen deposition associated with the appearance of myeloid cells and profibrotic gene activation. Renal fibrosis was not seen in Ang‐II‐infused TNFR1‐KO. By contrast, while hypertension increased and cardiac function decreased more slowly in TNFR1‐KO than WT, they were equivalently abnormal at 6 weeks. Similarly, serum markers for renal dysfunction were not different after 6 weeks. In conclusion, Ang‐II infusion initiated fibroinflammatory responses with different time courses in heart and kidney, both requiring TNFR1 signaling, and both associated with monocyte‐derived myeloid fibroblasts. TNFR1 deletion obviated the fibroinflammatory effects of Ang‐II, but did not alter changes in blood pressure and cardiorenal function after 6 weeks. Thus, the synergy of TNF with Ang‐II targets the fibroinflammatory component of Ang‐II signaling.

Tumor Necrosis FactorClinical Perspective

Background—Continuous angiotensin-II infusion induced the uptake of monocytic fibroblast precursors that initiated the development of cardiac fibrosis; these cells and concurrent fibrosis were absent in mice lacking tumor necrosis factor receptor 1 (TNFR1). We now investigated their cellular origin and temporal uptake and the involvement of TNFR1 in monocyte-to-fibroblast differentiation. Methods and Results—Within a day, angiotensin-II induced a proinflammatory environment characterized by production of inflammatory chemokines, cytokines, and TH1-interleukins and uptake of bone marrow-derived M1 cells. After a week, the cardiac environment changed to profibrotic with growth factor and TH2-interleukin synthesis, uptake of bone marrow–derived M2 cells, and the presence of M2-related fibroblasts. TNFR1 signaling was not necessary for early M1 uptake, but its absence diminished the amount of M2 cells. TNFR1-knockout hearts also showed reduced levels of cytokine expression, but not of TH-related lymphokines. Reconstitution of wild-type bone marrow into TNFR1-knockout mice was sufficient to restore M2 uptake, upregulation of proinflammatory and profibrotic genes, and development of fibrosis in response to angiotensin-II. We also developed an in vitro mouse monocyte-to-fibroblast maturation assay that confirmed the essential role of TNFR1 in the sequential progression of monocyte activation and fibroblast formation. Conclusions—Development of cardiac fibrosis in response to angiotensin-II was mediated by myeloid precursors and consisted of 2 stages. A primary M1 inflammatory response was followed by a subsequent M2 fibrotic response. Although the first phase seemed to be independent of TNFR1 signaling, the later phase (and development of fibrosis) was abrogated by deletion of TNFR1.Background— Continuous angiotensin-II infusion induced the uptake of monocytic fibroblast precursors that initiated the development of cardiac fibrosis; these cells and concurrent fibrosis were absent in mice lacking tumor necrosis factor receptor 1 (TNFR1). We now investigated their cellular origin and temporal uptake and the involvement of TNFR1 in monocyte-to-fibroblast differentiation. Methods and Results— Within a day, angiotensin-II induced a proinflammatory environment characterized by production of inflammatory chemokines, cytokines, and TH1-interleukins and uptake of bone marrow-derived M1 cells. After a week, the cardiac environment changed to profibrotic with growth factor and TH2-interleukin synthesis, uptake of bone marrow–derived M2 cells, and the presence of M2-related fibroblasts. TNFR1 signaling was not necessary for early M1 uptake, but its absence diminished the amount of M2 cells. TNFR1-knockout hearts also showed reduced levels of cytokine expression, but not of TH-related lymphokines. Reconstitution of wild-type bone marrow into TNFR1-knockout mice was sufficient to restore M2 uptake, upregulation of proinflammatory and profibrotic genes, and development of fibrosis in response to angiotensin-II. We also developed an in vitro mouse monocyte-to-fibroblast maturation assay that confirmed the essential role of TNFR1 in the sequential progression of monocyte activation and fibroblast formation. Conclusions— Development of cardiac fibrosis in response to angiotensin-II was mediated by myeloid precursors and consisted of 2 stages. A primary M1 inflammatory response was followed by a subsequent M2 fibrotic response. Although the first phase seemed to be independent of TNFR1 signaling, the later phase (and development of fibrosis) was abrogated by deletion of TNFR1.

Tumor Necrosis FactorClinical Perspective: A Mechanistic Link Between Angiotensin-II–Induced Cardiac Inflammation and Fibrosis

Background—Continuous angiotensin-II infusion induced the uptake of monocytic fibroblast precursors that initiated the development of cardiac fibrosis; these cells and concurrent fibrosis were absent in mice lacking tumor necrosis factor receptor 1 (TNFR1). We now investigated their cellular origin and temporal uptake and the involvement of TNFR1 in monocyte-to-fibroblast differentiation. Methods and Results—Within a day, angiotensin-II induced a proinflammatory environment characterized by production of inflammatory chemokines, cytokines, and TH1-interleukins and uptake of bone marrow-derived M1 cells. After a week, the cardiac environment changed to profibrotic with growth factor and TH2-interleukin synthesis, uptake of bone marrow–derived M2 cells, and the presence of M2-related fibroblasts. TNFR1 signaling was not necessary for early M1 uptake, but its absence diminished the amount of M2 cells. TNFR1-knockout hearts also showed reduced levels of cytokine expression, but not of TH-related lymphokines. Reconstitution of wild-type bone marrow into TNFR1-knockout mice was sufficient to restore M2 uptake, upregulation of proinflammatory and profibrotic genes, and development of fibrosis in response to angiotensin-II. We also developed an in vitro mouse monocyte-to-fibroblast maturation assay that confirmed the essential role of TNFR1 in the sequential progression of monocyte activation and fibroblast formation. Conclusions—Development of cardiac fibrosis in response to angiotensin-II was mediated by myeloid precursors and consisted of 2 stages. A primary M1 inflammatory response was followed by a subsequent M2 fibrotic response. Although the first phase seemed to be independent of TNFR1 signaling, the later phase (and development of fibrosis) was abrogated by deletion of TNFR1.Background— Continuous angiotensin-II infusion induced the uptake of monocytic fibroblast precursors that initiated the development of cardiac fibrosis; these cells and concurrent fibrosis were absent in mice lacking tumor necrosis factor receptor 1 (TNFR1). We now investigated their cellular origin and temporal uptake and the involvement of TNFR1 in monocyte-to-fibroblast differentiation. Methods and Results— Within a day, angiotensin-II induced a proinflammatory environment characterized by production of inflammatory chemokines, cytokines, and TH1-interleukins and uptake of bone marrow-derived M1 cells. After a week, the cardiac environment changed to profibrotic with growth factor and TH2-interleukin synthesis, uptake of bone marrow–derived M2 cells, and the presence of M2-related fibroblasts. TNFR1 signaling was not necessary for early M1 uptake, but its absence diminished the amount of M2 cells. TNFR1-knockout hearts also showed reduced levels of cytokine expression, but not of TH-related lymphokines. Reconstitution of wild-type bone marrow into TNFR1-knockout mice was sufficient to restore M2 uptake, upregulation of proinflammatory and profibrotic genes, and development of fibrosis in response to angiotensin-II. We also developed an in vitro mouse monocyte-to-fibroblast maturation assay that confirmed the essential role of TNFR1 in the sequential progression of monocyte activation and fibroblast formation. Conclusions— Development of cardiac fibrosis in response to angiotensin-II was mediated by myeloid precursors and consisted of 2 stages. A primary M1 inflammatory response was followed by a subsequent M2 fibrotic response. Although the first phase seemed to be independent of TNFR1 signaling, the later phase (and development of fibrosis) was abrogated by deletion of TNFR1.