Leukocyte integrin-dependent downregulation of the transcription factor FOXP1 is required for monocyte differentiation and macrophage functions, but the precise gene regulatory mechanism is unknown. ...Here, we identify multi-promoter structure (P1, P2, and P3) of the human FOXP1 gene. Clustering of the β2-leukocyte integrin Mac-1 downregulated transcription from these promoters. We extend our prior observation that IL-1 receptor-associated kinase 1 (IRAK1) is physically associated with Mac-1 and provide evidence that IRAK1 is a potent suppressor of human FOXP1 promoter. IRAK1 reduced phosphorylation of histone deacetylase 4 (HDAC4) via inhibiting phosphorylation of calcium/calmodulin dependent protein kinase II delta (CaMKIIδ), thereby promoting recruitment of HDAC4 to P1 chromatin. A novel human FOXP1 intronic transcript 1 (FOXP1-IT1) long non-coding RNA (lncRNA), whose gene is embedded within that of FOXP1, has been cloned and found to bind directly to HDAC4 and regulate FOXP1 in cis manner. Overexpression of FOXP1-IT1 counteracted Mac-1 clustering-dependent downregulation of FOXP1, reduced IRAK1 downregulation of HDAC4 phosphorylation, and attenuated differentiation of THP-1 monocytic cells. In contrast, Mac-1 clustering inhibited FOXP1-IT1 expression with reduced binding to HDAC4 as well as phosphorylation of CaMKIIδ to activate the IRAK1 signaling pathway. Importantly, both IRAK1 and HDAC4 inhibitors significantly reduced integrin clustering-triggered downregulation of FOXP1 expression in purified human blood monocytes. Identification of this Mac-1/IRAK-1/FOXP1-IT1/HDAC4 signaling network featuring crosstalk between lncRNA and epigenetic factor for the regulation of FOXP1 expression provides new targets for anti-inflammatory therapeutics.
•Identification of functional multi-promoter structure of the human FOXP1 gene•“Outside-in” integrin signaling downregulates promoter activity of FOXP1 via IRAK1.•IRAK1-CaMKIIδ-HDAC4 cascade enhances HDAC4 recruitment to FOXP1 promoter chromatin.•FOXP1-IT1 lncRNA associates with HDAC4 to mediate integrin-triggered IRAK1 pathway.•Integrin-IRAK1-HDAC4 regulation of FOXP1 exists in authentic human blood monocytes.
Diurnal variation in nitrogen homeostasis is observed across phylogeny. But whether these are endogenous rhythms, and if so, molecular mechanisms that link nitrogen homeostasis to the circadian clock ...remain unknown. Here, we provide evidence that a clock-dependent peripheral oscillator, Krüppel-like factor 15 transcriptionally coordinates rhythmic expression of multiple enzymes involved in mammalian nitrogen homeostasis. In particular, Krüppel-like factor 15-deficient mice exhibit no discernable amino acid rhythm, and the rhythmicity of ammonia to urea detoxification is impaired. Of the external cues, feeding plays a dominant role in modulating Krüppel-like factor 15 rhythm and nitrogen homeostasis. Further, when all behavioral, environmental and dietary cues were controlled in humans, nitrogen homeostasis exhibited an endogenous circadian rhythmicity. Thus, in mammals, nitrogen homeostasis exhibits circadian rhythmicity, and is orchestrated by Krüppel-like factor 15.
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► Nitrogen homeostasis exhibits circadian rhythmicity in mammals ► Klf 15 regulates rhythmic amino acid utilization and ammonia detoxification ► Krüppel-like factor 15 is regulated by the circadian clock ► Feeding is a major external cue regulating Klf15 rhythmicity and nitrogen homeostasis
The ability of skeletal muscle to enhance lipid utilization during exercise is a form of metabolic plasticity essential for survival. Conversely, metabolic inflexibility in muscle can cause organ ...dysfunction and disease. Although the transcription factor Kruppel-like factor 15 (KLF15) is an important regulator of glucose and amino acid metabolism, its endogenous role in lipid homeostasis and muscle physiology is unknown. Here we demonstrate that KLF15 is essential for skeletal muscle lipid utilization and physiologic performance. KLF15 directly regulates a broad transcriptional program spanning all major segments of the lipid-flux pathway in muscle. Consequently, Klf15-deficient mice have abnormal lipid and energy flux, excessive reliance on carbohydrate fuels, exaggerated muscle fatigue, and impaired endurance exercise capacity. Elucidation of this heretofore unrecognized role for KLF15 now implicates this factor as a central component of the transcriptional circuitry that coordinates physiologic flux of all three basic cellular nutrients: glucose, amino acids, and lipids.
Skeletal muscle is a major determinant of systemic metabolic homeostasis that plays a critical role in glucose metabolism and insulin sensitivity. By contrast, despite being a major user of fatty ...acids, and evidence that muscular disorders can lead to abnormal lipid deposition (e.g., nonalcoholic fatty liver disease in myopathies), our understanding of skeletal muscle regulation of systemic lipid homeostasis is not well understood. Here we show that skeletal muscle Krüppel-like factor 15 (KLF15) coordinates pathways central to systemic lipid homeostasis under basal conditions and in response to nutrient overload. Mice with skeletal muscle-specific KLF15 deletion demonstrated (a) reduced expression of key targets involved in lipid uptake, mitochondrial transport, and utilization, (b) elevated circulating lipids, (c) insulin resistance/glucose intolerance, and (d) increased lipid deposition in white adipose tissue and liver. Strikingly, a diet rich in short-chain fatty acids bypassed these defects in lipid flux and ameliorated aspects of metabolic dysregulation. Together, these findings establish skeletal muscle control of lipid flux as critical to systemic lipid homeostasis and metabolic health.
The mammalian heart, the body's largest energy consumer, has evolved robust mechanisms to tightly couple fuel supply with energy demand across a wide range of physiologic and pathophysiologic states, ...yet, when compared with other organs, relatively little is known about the molecular machinery that directly governs metabolic plasticity in the heart. Although previous studies have defined Kruppel-like factor 15 (KLF15) as a transcriptional repressor of pathologic cardiac hypertrophy, a direct role for the KLF family in cardiac metabolism has not been previously established. We show in human heart samples that KLF15 is induced after birth and reduced in heart failure, a myocardial expression pattern that parallels reliance on lipid oxidation. Isolated working heart studies and unbiased transcriptomic profiling in Klf15-deficient hearts demonstrate that KLF15 is an essential regulator of lipid flux and metabolic homeostasis in the adult myocardium. An important mechanism by which KLF15 regulates its direct transcriptional targets is via interaction with p300 and recruitment of this critical co-activator to promoters. This study establishes KLF15 as a key regulator of myocardial lipid utilization and is the first to implicate the KLF transcription factor family in cardiac metabolism.
Metabolic homeostasis is central to normal cardiac function. The molecular mechanisms underlying metabolic plasticity in the heart remain poorly understood.
Kruppel-like factor 15 (KLF15) is a direct and independent regulator of myocardial lipid flux.
KLF15 is a core component of the transcriptional circuitry that governs cardiac metabolism.
This work is the first to implicate the KLF transcription factor family in cardiac metabolism.
Abdominal aortic aneurysm (AAA) is a major cause of morbidity and mortality; however, the mechanisms that are involved in disease initiation and progression are incompletely understood. Extracellular ...matrix proteins play an integral role in modulating vascular homeostasis in health and disease. Here, we determined that the expression of the matricellular protein CCN3 is strongly reduced in rodent AAA models, including angiotensin II-induced AAA and elastase perfusion-stimulated AAA. CCN3 levels were also reduced in human AAA biopsies compared with those in controls. In murine models of induced AAA, germline deletion of Ccn3 resulted in severe phenotypes characterized by elastin fragmentation, vessel dilation, vascular inflammation, dissection, heightened ROS generation, and smooth muscle cell loss. Conversely, overexpression of CCN3 mitigated both elastase- and angiotensin II-induced AAA formation in mice. BM transplantation experiments suggested that the AAA phenotype of CCN3-deficient mice is intrinsic to the vasculature, as AAA was not exacerbated in WT animals that received CCN3-deficient BM and WT BM did not reduce AAA severity in CCN3-deficient mice. Genetic and pharmacological approaches implicated the ERK1/2 pathway as a critical regulator of CCN3-dependent AAA development. Together, these results demonstrate that CCN3 is a nodal regulator in AAA biology and identify CCN3 as a potential therapeutic target for vascular disease.
Recent studies implicate the Cyr61, CTGF, Nov (CCN) matricellular signaling protein family as emerging players in vascular biology, with NOV (alias CCN3) as an important regulator of vascular ...homeostasis. Herein, we examined the role of CCN3 in the pathogenesis of atherosclerosis. In response to a 15-week high-fat diet feeding, CCN3-deficient mice on the atherosclerosis-prone Apoe−/− background developed increased aortic lipid-rich plaques compared to control Apoe−/− mice, a result that was observed in the absence of alterations in plasma lipid content. To address the cellular contributor(s) responsible for the atherosclerotic phenotype, we performed bone marrow transplantation experiments. Transplantation of Apoe ; Ccn3 double-knockout bone marrow into Apoe−/− mice resulted in an increase of atherosclerotic plaque burden, whereas transplantation of Apoe−/− marrow to Apoe ; Ccn3 double-knockout mice caused a reduction of atherosclerosis. These results indicate that CCN3 deficiency, specifically in the bone marrow, plays a major role in the development of atherosclerosis. Mechanistically, cell-based studies in isolated peritoneal macrophages demonstrated that CCN3 deficiency leads to an increase of lipid uptake and foam cell formation, an effect potentially attributed to the increased expression of scavenger receptors CD36 and SRA1, key factors involved in lipoprotein uptake. These results suggest that bone marrow–derived CCN3 is an essential regulator of atherosclerosis and point to a novel role of CCN3 in modulating lipid accumulation within macrophages.
Vascular calcification is a multifaceted process involving gain of calcification inducers and loss of calcification inhibitors. One such inhibitor is inorganic pyrophosphate (PP(i)), and regulated ...generation and homeostasis of extracellular PP(i) is a critical determinant of soft-tissue mineralization. We recently described an autocrine mechanism of extracellular PP(i) generation in cultured rat aortic vascular smooth muscle cells (VSMC) that involves both ATP release coupled to the ectophosphodiesterase/pyrophosphatase ENPP1 and efflux of intracellular PP(i) mediated or regulated by the plasma membrane protein ANK. We now report that increased cAMP signaling and elevated extracellular inorganic phosphate (P(i)) act synergistically to induce calcification of these VSMC that is correlated with progressive reduction in ability to accumulate extracellular PP(i). Attenuated PP(i) accumulation was mediated in part by cAMP-dependent decrease in ANK expression coordinated with cAMP-dependent increase in expression of TNAP, the tissue nonselective alkaline phosphatase that degrades PP(i). Stimulation of cAMP signaling did not alter ATP release or ENPP1 expression, and the cAMP-induced changes in ANK and TNAP expression were not sufficient to induce calcification. Elevated extracellular P(i) alone elicited only minor calcification and no significant changes in ANK, TNAP, or ENPP1. In contrast, combined with a cAMP stimulus, elevated P(i) induced decreases in the ATP release pathway(s) that supports ENPP1 activity; this resulted in markedly reduced rates of PP(i) accumulation that facilitated robust calcification. Calcified VSMC were characterized by maintained expression of multiple SMC differentiation marker proteins including smooth muscle (SM) alpha-actin, SM22alpha, and calponin. Notably, addition of exogenous ATP (or PP(i) per se) rescued cAMP + phosphate-treated VSMC cultures from progression to the calcified state. These observations support a model in which extracellular PP(i) generation mediated by both ANK- and ATP release-dependent mechanisms serves as a critical regulator of VSMC calcification.
The metabolic myocardium is an omnivore and utilizes various carbon substrates to meet its energetic demand. While the adult heart preferentially consumes fatty acids (FAs) over carbohydrates, ...myocardial fuel plasticity is essential for organismal survival. This metabolic plasticity governing fuel utilization is under robust transcriptional control and studies over the past decade have illuminated members of the nuclear receptor family of factors (e.g., PPARα) as important regulators of myocardial lipid metabolism. However, given the complexity of myocardial metabolism in health and disease, it is likely that other molecular pathways are likely operative and elucidation of such pathways may provide the foundation for novel therapeutic approaches. We previously demonstrated that Kruppel-like factor 15 (KLF15) is an independent regulator of cardiac lipid metabolism thus raising the possibility that KLF15 and PPARα operate in a coordinated fashion to regulate myocardial gene expression requisite for lipid oxidation. In the current study, we show that KLF15 binds to, cooperates with, and is required for the induction of canonical PPARα-mediated gene expression and lipid oxidation in cardiomyocytes. As such, this study establishes a molecular module involving KLF15 and PPARα and provides fundamental insights into the molecular regulation of cardiac lipid metabolism.
The circadian glucocorticoid-Krüppel-like factor 15-branched-chain amino acid (GC-KLF15-BCAA) signaling pathway is a key regulatory axis in muscle, whose imbalance has wide-reaching effects on ...metabolic homeostasis. Spinal muscular atrophy (SMA) is a neuromuscular disorder also characterized by intrinsic muscle pathologies, metabolic abnormalities and disrupted sleep patterns, which can influence or be influenced by circadian regulatory networks that control behavioral and metabolic rhythms. We therefore set out to investigate the contribution of the GC-KLF15-BCAA pathway in SMA pathophysiology of Taiwanese Smn−/−;SMN2 and Smn2B/− mouse models. We thus uncover substantial dysregulation of GC-KLF15-BCAA diurnal rhythmicity in serum, skeletal muscle and metabolic tissues of SMA mice. Importantly, modulating the components of the GC-KLF15-BCAA pathway via pharmacological (prednisolone), genetic (muscle-specific Klf15 overexpression) and dietary (BCAA supplementation) interventions significantly improves disease phenotypes in SMA mice. Our study highlights the GC-KLF15-BCAA pathway as a contributor to SMA pathogenesis and provides several treatment avenues to alleviate peripheral manifestations of the disease. The therapeutic potential of targeting metabolic perturbations by diet and commercially available drugs could have a broader implementation across other neuromuscular and metabolic disorders characterized by altered GC-KLF15-BCAA signaling.
•SMA is a neuromuscular disease characterized by motoneuron loss, muscle abnormalities and metabolic perturbations.•The regulatory GC-KLF15-BCAA pathway is dysregulated in serum and skeletal muscle of SMA mice during disease progression.•Modulating GC-KLF15-BCAA signaling by pharmacological, dietary and genetic interventions improves phenotype of SMA mice.
Spinal muscular atrophy (SMA) is a devastating and debilitating childhood genetic disease. Although nerve cells are mainly affected, muscle is also severely impacted. The normal communication between the glucocorticoid (GC) hormone, the protein KLF15 and the dietary branched-chain amino acids (BCAAs) maintains muscle and whole-body health. In this study, we identified an abnormal activity of GC-KLF15- BCAA in blood and muscle of SMA mice. Importantly, targeting GC-KLF15-BCAA activity with an existing drug or a specific diet improved disease progression in SMA mice. Our research uncovers GCs, KLF15 and BCAAs as therapeutic targets to ameliorate SMA muscle and whole-body health.
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