Elevated Systemic Hepcidin and Iron Depletion in Obese Premenopausal Females

Hepcidin, the body's main regulator of systemic iron homeostasis, is upregulated in response to inflammation and is thought to play a role in the manifestation of iron deficiency (ID) observed in obese populations. We determined systemic hepcidin levels and its association with body mass, inflammation, erythropoiesis, and iron status in premenopausal obese and nonobese women (n = 20/group) matched for hemoglobin (Hb). The obese participants also had liver and abdominal visceral and subcutaneous adipose tissue assessed for tissue iron accumulation and hepcidin mRNA expression. Despite similar Hb levels, the obese women had significantly higher serum hepcidin (88.02 vs. 9.70 ng/ml; P < 0.0001) and serum transferrin receptor (sTfR) (P = 0.001) compared to nonobese. In the obese women hepcidin was not correlated with serum iron (r = ?0.02), transferrin saturation (Tsat) (r = 0.17) or sTfR (r = ?0.12); in the nonobese it was significantly positively correlated with Tsat (r = 0.70) and serum iron (r = 0.58), and inversely with sTfR (r = ?0.63). Detectable iron accumulation in the liver and abdominal adipose tissue of the obese women was minimal. Liver hepcidin mRNA expression was ～700 times greater than adipose tissue production and highly correlated with circulating hepcidin levels (r = 0.61). Serum hepcidin is elevated in obese women despite iron depletion, suggesting that it is responding to inflammation rather than iron status. The source of excess hepcidin appears to be the liver and not adipose tissue. The ID of obesity is predominantly a condition of a true body iron deficit rather than maldistribution of iron due to inflammation. However, these findings suggest inflammation may perpetuate this condition by hepcidin‐mediated inhibition of dietary iron absorption.     

Inflammation Regulates TMPRSS6 Expression via STAT5

TMPRSS6 is a regulated gene, with a crucial role in the regulation of iron homeostasis by inhibiting hepcidin expression. The main regulator of iron homeostasis, the antimicrobial peptide hepcidin, which also has a role in immunity, is directly upregulated by inflammation. In this study, we analyzed whether inflammation is also a modulator of TMPRSS6 expression in vitro and in vivo and we determined the mechanism of this regulation A Human Hepatoma cell line was treated with interleukin-6 and mice were injected with lipopolysaccharide and TMPRSS6 expression and the regulatory mechanism were addressed. In this study, we demonstrate that inflammation downregulates TMPRSS6 expression in vitro and in vivo. The downregulation of Tmprss6 by inflammation in mice is not dependent on the Bmp-Smad pathway but occurs through a decrease in Stat5 phosphorylation. Moreover, Stat5 positively regulates Tmprss6 expression directly by binding to a Stat5 element located on the Tmprss6 promoter. Importantly, our results highlight the functional role of inflammatory modulation of TMPRSS6 expression in the regulation of hepcidin. TMPRSS6 inhibition via decreased STAT5 phosphorylation may be an additional mechanism by which inflammation stimulates hepcidin expression to regulate iron homeostasis and immunity.     

Bmp6 Expression in Murine Liver Non Parenchymal Cells: A Mechanism to Control their High Iron Exporter Activity and Protect Hepatocytes from Iron Overload?

Bmp6 is the main activator of hepcidin, the liver hormone that negatively regulates plasma iron influx by degrading the sole iron exporter ferroportin in enterocytes and macrophages. Bmp6 expression is modulated by iron but the molecular mechanisms are unknown. Although hepcidin is expressed almost exclusively by hepatocytes (HCs), Bmp6 is produced also by non-parenchymal cells (NPCs), mainly sinusoidal endothelial cells (LSECs). To investigate the regulation of Bmp6 in HCs and NPCs, liver cells were isolated from adult wild type mice whose diet was modified in iron content in acute or chronic manner and in disease models of iron deficiency (Tmprss6 KO mouse) and overload (Hjv KO mouse). With manipulation of dietary iron in wild-type mice, Bmp6 and Tfr1 expression in both HCs and NPCs was inversely related, as expected. When hepcidin expression is abnormal in murine models of iron overload (Hjv KO mice) and deficiency (Tmprss6 KO mice), Bmp6 expression in NPCs was not related to Tfr1. Despite the low Bmp6 in NPCs from Tmprss6 KO mice, Tfr1 mRNA was also low. Conversely, despite body iron overload and high expression of Bmp6 in NPCs from Hjv KO mice, Tfr1 mRNA and protein were increased. However, in the same cells ferritin L was only slightly increased, but the iron content was not, suggesting that Bmp6 in these cells reflects the high intracellular iron import and export. We propose that NPCs, sensing the iron flux, not only increase hepcidin through Bmp6 with a paracrine mechanism to control systemic iron homeostasis but, controlling hepcidin, they regulate their own ferroportin, inducing iron retention or release and further modulating Bmp6 production in an autocrine manner. This mechanism, that contributes to protect HC from iron loading or deficiency, is lost in disease models of hepcidin production.     

Glucose acts as a regulator of serum iron by increasing serum hepcidin concentrations

Mutual clinical and molecular interactions between iron and glucose metabolism have been reported. We aimed to investigate a potential effect of glucose on iron homeostasis. We found that serum iron concentrations gradually decreased over 180 min after the administration of 75 g of glucose from 109.8±45.4 mg/L to 94.4±40.4 mg/L (P<.001; N= 40) but remained unchanged in control subjects receiving tap water (N= 21). Serum hepcidin, the key iron regulatory hormone which is mainly derived from hepatocytes but also expressed in pancreatic β-cells, increased within 120 min after glucose ingestion from 19.7±9.9 nmol/L to 31.4±21.0 nmol/L (P<.001). In cell culture, glucose induced the secretion of hepcidin and insulin into the supernatant of INS-1E cultures, but did not change the amount of hepcidin detectable in the hepatocyte cell culture HepG2. We additionally confirmed the expression of hepcidin in a human islet cell preparation. These results suggest that glucose acts as a regulator of serum iron concentrations, most likely by triggering the release of hepcidin from β-cells.     

Smad6 and Smad7 are co-regulated with hepcidin in mouse models of iron overload

The inhibitory Smad7 acts as a critical suppressor of hepcidin, the major regulator of systemic iron homeostasis. In this study we define the mRNA expression of the two functionally related Smad proteins, Smad6 and Smad7, within pathways known to regulate hepcidin levels. Using mouse models for hereditary hemochromatosis (Hfe-, TfR2-, Hfe/TfR2-, Hjv- and hepcidin1-deficient mice) we show that hepcidin, Smad6 and Smad7 mRNA expression is coordinated in such a way that it correlates with the activity of the Bmp/Smad signaling pathway rather than with liver iron levels. This regulatory circuitry is disconnected by iron treatment of Hfe ?/? and Hfe/TfR2 mice that significantly increases hepatic iron levels as well as hepcidin, Smad6 and Smad7 mRNA expression but fails to augment pSmad1/5/8 levels. This suggests that additional pathways contribute to the regulation of hepcidin, Smad6 and Smad7 under these conditions which do not require Hfe.     

Decreased Serum Hepcidin and Improved Functional Iron Status 6 Months After Restrictive Bariatric Surgery

Excess adiposity is associated with low‐grade inflammation and decreased iron status. Iron depletion in obesity is thought to be mediated by an inflammation‐induced increase in the body's main regulator of iron homeostasis, hepcidin. Elevated hepcidin can result in iron depletion as it prevents the release of dietary iron absorbed into the enterocytes, limiting replenishment of body iron losses. Weight reduction is associated with decreased inflammation; however, the impact of reduced inflammation on iron status and systemic hepcidin in obese individuals remains unknown. We determined prospectively the impact of weight loss on iron status parameters, serum hepcidin, inflammation, and dietary iron in 20 obese premenopausal females 6 months after restrictive bariatric surgery. At baseline, the presence of iron depletion was high with 45% of the women having serum transferrin receptor (sTfR) >28.1 nmol/l. Differences between baseline and 6 months after surgery for BMI (47.56 vs. 39.55 kg/m²; P < 0.0001), C‐reactive protein (CRP) (10.83 vs. 5.71 mg/l; P < 0.0001), sTfR (29.97 vs. 23.08 nmol/l; P = 0.001), and serum hepcidin (111.25 vs. 31.35 ng/ml; P < 0.0001) were significantly lower, whereas hemoglobin (Hb) (12.10 vs. 13.30 g/dl; P < 0.0001) and hematocrit (Hct) (36.58 vs. 38.78%; P = 0.001) were significantly higher. Ferritin and transferrin saturation (Tsat) showed minimal improvement at follow‐up. At baseline, hepcidin was not correlated with sTfR (r = 0.02); however, at follow‐up, significant correlations were found (r = ?0.58). Change in interleukin‐6 (IL‐6) from baseline was marginally associated with decreased log serum hepcidin (Δ IL‐6: β = ?0.22; P = 0.15), whereas change in BMI or weight was not. No significant difference in dietary iron was noted after surgery. Weight loss in obese premenopausal women is associated with reduced serum hepcidin and inflammation. Reduction in inflammation and hepcidin likely allow for enhanced dietary iron absorption resulting in an improved functional iron profile.     

The dietary flavonoid myricetin regulates iron homeostasis by suppressing hepcidin expression

Hepcidin, a master regulator of iron homeostasis, is a promising target in treatment of iron disorders such as hemochromatosis, anemia of inflammation and iron-deficiency anemia. We previously reported that black soybean seed coat extract could inhibit hepcidin expression. Based on this finding, we performed a screen in cultured cells in order to identify the compounds in black soybeans that inhibit hepcidin expression. We found that the dietary flavonoid myricetin significantly inhibited the expression of hepcidin both in vitro and in vivo. Treating cultured cells with myricetin decreased both HAMP mRNA levels and promoter activity by reducing SMAD1/5/8 phosphorylation. This effect was observed even in the presence of bone morphogenic protein-6 (BMP6) and interleukin-6 (IL-6), two factors that stimulate hepcidin expression. Furthermore, mice that were treated with myricetin (either orally or systemically) had reduced hepatic hepcidin expression, decreased splenic iron levels and increased serum iron levels. Notably, myricetin-treated mice increased red blood cell counts and hemoglobin levels. In addition, pretreating mice with myricetin prevented LPS-induced hypoferremia. We conclude that myricetin potently inhibits hepcidin expression both in vitro and in vivo, and this effect is mediated by altering BMP/SMAD signaling. These experiments highlight the feasibility of identifying and characterizing bioactive phytochemicals to suppress hepcidin expression. These results also suggest that myricetin may represent a novel therapy for treating iron deficiency-related diseases.     

The Role of Hepatocyte Hemojuvelin in the Regulation of Bone Morphogenic Protein-6 and Hepcidin Expression in Vivo

Both hemojuvelin (HJV) and bone morphogenic protein-6 (BMP6) are essential for hepcidin expression. Hepcidin is the key peptide hormone in iron homeostasis, and is secreted predominantly by hepatocytes. HJV expression is detected in hepatocytes, as well as in skeletal and heart muscle. HJV binds BMP6 and increases hepcidin expression presumably by acting as a BMP co-receptor. We characterized the role of hepatocyte HJV in the regulation of BMP6 and hepcidin expression. In HJV-null (Hjv^−/−) mice that have severe iron overload and marked suppression of hepcidin expression, we detected 4-fold higher hepatic BMP6 mRNA than in wild-type counterparts. These results indicate that Hjv^−/− mice do not lack BMP6. Furthermore, iron depletion in Hjv^−/− mice decreased hepatic BMP6 mRNA. Expression of HJV in hepatocytes of Hjv^−/− mice using an AAV2/8 vector, increased hepatic hepcidin mRNA by 65-fold and phosphorylated Smad1/5/8 in the liver by about 2.5-fold. However, no significant change in BMP6 mRNA was detected in either the liver or the small intestine of these animals. Our results revealed a close correlation of hepatic BMP6 mRNA expression with hepatic iron-loading. Together, our data indicate that the regulation of hepatic BMP6 expression by iron is independent of HJV, and that expression of HJV in hepatocytes plays an essential role in hepcidin expression by potentiating the BMP6-mediated signaling.     

Bone morphogenetic protein 6–mediated crosstalk between endothelial cells and hepatocytes recapitulates the iron-sensing pathway in vitro

Liver sinusoidal endothelial cell–derived bone morphogenetic protein 6 (BMP6) and the BMP6–small mothers against decapentaplegic homolog (SMAD) signaling pathway are essential for the expression of hepcidin, the secretion of which is considered the systemic master switch of iron homeostasis. However, there are continued controversies related to the strong and direct suppressive effect of iron on hepatocellular hepcidin in vitro in contrast to in vivo conditions. Here, we directly studied the crosstalk between endothelial cells (ECs) and hepatocytes using in vitro coculture models that mimic hepcidin signaling in vivo. Huh7 cells were directly cocultured with ECs, and EC conditioned media (CM) were also used to culture Huh7 cells and primary mouse hepatocytes. To explore the reactions of ECs to surrounding iron, they were grown in the presence of ferric ammonium citrate and heme, two iron-containing molecules. We found that both direct coculture with ECs and EC-CM significantly increased hepcidin expression in Huh7 cells. The upstream SMAD pathway, including phosphorylated SMAD1/5/8, SMAD1, and inhibitor of DNA binding 1, was induced by EC-CM, promoting hepcidin expression. Efficient blockage of this EC-mediated hepcidin upregulation by an inhibitor of the BMP6 receptor ALK receptor tyrosine kinase 2/3 or BMP6 siRNA identified BMP6 as a major hepcidin regulator in this coculture system, which highly fits the model of hepcidin regulation by iron in vivo. In addition, EC-derived BMP6 and hepcidin were highly sensitive to levels of not only ferric iron but also heme as low as 500 nM. We here establish a hepatocyte–endothelial coculture system to fully recapitulate iron regulation by hepcidin using EC-derived BMP6.     

Hydrodynamic-based delivery of an interleukin-22-Ig fusion gene ameliorates experimental autoimmune myocarditis in rats

IL-22 is one of several cytokines with limited homology to IL-10. However, the biological activities of IL-22 are mostly unknown. The purpose of this study was to evaluate the effect of IL-22 on rat experimental autoimmune myocarditis (EAM) and elucidate an aspect of the biological activities of IL-22. Rats were immunized on day 0; IL-22-Ig-treated rats were injected with pCAGGS-IL-22-Ig and control rats with pCAGGS-Ig using hydrodynamics-based gene delivery on day 1 or day 6. IL-22-Ig gene therapy administered on day 1 or day 6 after immunization was effective in controlling EAM as monitored by the heart weight to body weight ratio, and the myocarditis area in rats was sacrificed on day 17. Examination of the expression of IL-22-related genes in purified cells from EAM hearts suggested that IL-22-Ig acting target cells were noncardiomyocytic (NC) noninflammatory cells such as fibroblasts, smooth muscle cells, and endothelial cells. Therefore, we examined the effect of rIL-22 or serum containing IL-22-Ig on the expression of immune-relevant genes in IL-1-stimulated NC cells cultured from EAM hearts. Results showed that the expression of immunologic molecules (PGE synthase, cyclooxygenase-2, MIP-2, MCP-1, IL-6, and cytokine-induced neutrophil chemoattractant-2) in IL-1-stimulated NC cells was significantly decreased by rIL-22 or serum containing IL-22-Ig. EAM was suppressed by hydrodynamics-based delivery of plasmid DNA encoding IL-22-Ig, and the reason for this effectiveness may be that IL-22 suppressed gene expression of PG synthases, IL-6, and chemokines in activated NC noninflammatory cells.     

Hepatocyte-specific deletion of peroxisomal protein PEX13 results in disrupted iron homeostasis

Peroxisomes are organelles, abundant in the liver, involved in a variety of cellular functions, including fatty acid metabolism, plasmalogen synthesis and metabolism of reactive oxygen species. Several inherited disorders are associated with peroxisomal dysfunction; increasingly many are associated with hepatic pathologies. The liver plays a principal role in regulation of iron metabolism. In this study we examined the possibility of a relationship between iron homeostasis and peroxisomal integrity.We examined the effect of deleting Pex13 in mouse liver on systemic iron homeostasis. We also used siRNA-mediated knock-down of PEX13 in a human hepatoma cell line (HepG2/C3A) to elucidate the mechanisms of PEX13-mediated regulation of hepcidin.We demonstrate that transgenic mice lacking hepatocyte Pex13 have defects in systemic iron homeostasis. The ablation of Pex13 expression in hepatocytes leads to a significant reduction in hepatic hepcidin levels. Our results also demonstrate that a deficiency of PEX13 gene expression in HepG2/C3A cells leads to decreased hepcidin expression, which is mediated through an increase in the signalling protein SMAD7, and endoplasmic reticulum (ER) stress.This study identifies a novel role for a protein involved in maintaining peroxisomal integrity and function in iron homeostasis. Loss of Pex13, a protein important for peroxisomal function, in hepatocytes leads to a significant increase in ER stress, which if unresolved, can affect liver function. The results from this study have implications for the management of patients with peroxisomal disorders and the liver-related complications they may develop.     

Calcitonin increases hepatic hepcidin expression through the BMP6 of kidney in mice

BackgroundOsteoporosis is frequently accompanied by iron disorders. Calcitonin (CT) was approved as a clinical drug to treat osteoporosis. Hepcidin is a peptide hormone that is secreted by the liver and controls body iron homeostasis. Hepcidin deficiency leads to iron overload diseases. This study was aimed at investigating the effect of CT on hepatic hepcidin and the mechanism by which CT modulates hepatic hepcidin pathways and iron metabolism.MethodRT-PCR, Western blot, ELISA and siRNA were used to detect the effect of CT on iron metabolism in vivo and in vitro. In addition, the regulatory signal molecules of hepcidin were measured to explore the molecular mechanism of its regulation.ResultsThe results showed that CT strongly increased hepcidin expression and altered iron homeostasis, after mice were intraperitoneal injection of CT. In response to CT administration, BMP6 level in kidney and the serum BMP6 was increased significantly. The phosphorylation of Smad1/5/8 proteins in liver was increased at 3 h and 6 h. Moreover, the Bmp inhibitor LDN-193,189 pretreatment significantly attenuated the CT-mediated increases in phosphorylated Smad1/5/8 and Hamp1 mRNA levels. Calcitonin receptor (CTR) siRNA transfection significant suppressed the role of CT on BMP6 expression in Caki-1 cells.ConclusionOur results suggest that CT strongly induces hepcidin expression and affected iron metabolism. It will provide a new strategy for the treatment of calcium iron related diseases.     

Gluconeogenic signals regulate hepcidin gene expression via a CRBN-KLF15 axis

Hepcidin (HAMP) is synthesized in the liver. It is a key iron-regulatory hormone that controls systemic iron homeostasis. Cereblon (CRBN) and Kruppel-like factor 15 (KLF15) are known to regulate diverse physiological functions. In this study, we investigated the role of CRBN on hepatic hepcidin gene expression and production under gluconeogenic stimuli. Fasted mice as well as forskolin (FSK)- and glucagon (GLU)-treated mice had reduced serum iron levels but increased expression levels of hepatic Crbn and Klf15 and hepcidin secretion. MicroRNA (miRNA) expression analysis of fasted and Ad-Crbn-infected mice revealed significant reduction of microRNA-639 (miR-639). Hepatic overexpression of Crbn elevated hepcidin expression and production along with Klf15 gene expression, whereas knockdown of Crbn and Klf15 markedly decreased FSK- and fasting-mediated induction of hepcidin gene expression and its biosynthesis in mouse livers and primary hepatocytes. Moreover, expression of KLF15 significantly increased the activity of hepcidin reporter gene. It was exclusively dependent on the KLF15-binding site identified within the hepcidin gene promoter. Overall, this study demonstrates that CRBN and KLF15 are novel mediators of gluconeogenic signal-induced hepcidin gene expression and production. Thus, CRBN and KLF15 might be novel potential therapeutic targets to intervene metabolic dysfunction.     

LncRNA UCA1 protects cardiomyocytes against hypoxia/reoxygenation induced apoptosis through inhibiting miR-143/MDM2/p53 axis

BackgroundlncUCA1 is abundantly expressed in the heart, indicating it may be important in maintaining normal myocardial function. However, the underlying mechanism of lncUCA1 in heart disease, particularly myocardial infarction (MI), is still in its infancy.MethodsLncUCA1 and miR-143 expression were measured in hearts of MI models. Overexpression and knockdown of lncUCA1 in neonatal rat cardiomyocytes were performed to confirm the effects of lncUCA1 in hypoxia-induced apoptosis.ResultsThe expression of lncUCA1 decreased but miR-143 increased inversely in MI heart. Overexpressing lncUCA1 protected cardiomyocytes from H/R induced apoptosis via inhibiting miR-143, which regulates apoptosis by targeting MDM2/p53 pathway. While silencing lncUCA1 caused miR-143 upregulation and H/R-induced apoptosis increase. Moreover, miR-143 was proved to be a competitive target of lncUCA1.ConclusionslncUCA1 might protect cardiomyocyte against H/R induced apoptosis by suppressing miR-143 and modulated the following downstream MDM2/p53 signaling pathway, indicating the therapeutic potential of targeting lncUCA1 for MI.     

Bone marrow stromal cell transplantation combined with angiotensin-converting enzyme inhibitor treatment in rat with acute myocardial infarction and the role of insulin-like growth factor-1

Background aimsWe investigated bone marrow stromal cell (BMSC) transplantation combined with angiotensin-converting enzyme inhibitor (ACEI) treatment in acute myocardial infarction (AMI) and the role of insulin-like growth factor-1 (IGF-1)MethodsAMI models were established in Sprague–Dawley rats by ligation of the left anterior descending coronary artery and grouped into blank control (BC), ACEI treatment (ACEI), BMSC transplantation (BMSC) and BMSC transplantation plus ACEI (combined). Perindopril (2.5 mg/kg) was administered by gavage to ACEI and combined groups from the day after AMI. BMSC (2 × 10⁸) were injected into the border of the MI area a week later in the BMSC and combined groups.ResultsAfter 4 weeks, hemodynamics in the BMSC and combined groups were significantly improved (P < 0.05 versus BC), with the greatest improvement in the combined group (P < 0.05). In addition, an increased number of BMSC survived in the combined group (P < 0.05 versus BMSC). A proportion of BMSC was positive for troponin T, as detected by immunofluorescence. The number of apoptotic cardiomyocytes was decreased in the BMSC and ACEI groups, and even further in the combined group (P < 0.05). IGF-1 expression was up-regulated in the BMSC and combined groups (P < 0.05 versus BC), but not in the ACEI group. B cell lymphoma-2 (Bcl-2) expression was up-regulated in the ACEI, BMSC and combined groups, with the highest expression in the combined group (P < 0.05).ConclusionsOur results show that BMSC engrafted in AMI can survive well and secrete IGF-1 and preserve cardiac function significantly. These data suggest that BMSC transplantation inhibits apoptosis of cardiomyocytes by up-regulation of Bcl-2 expression in the myocardium, and this effect might be sensitized by ACEI.     

Molecular analysis of homeostatic iron regulator,transmembrane protease serine-6, and BTB domain-containing protein-9 variants and iron parameters in blood donors

Genetic variants associated with iron homeostasis have been identified, but their association with iron-related indices and variables among different ethnic populations remains controversial. We aimed to explore the genotype frequency and allelic distribution of three iron-metabolism related variants in homeostatic iron regulator gene (HFE; rs1800562 G/A), transmembrane protease, Serine-6 gene (TMPRSS6; rs855791 A/G), and BTB domain-containing protein-9 gene (BTBD9; rs9357271 C/T) among a sample of the Middle Eastern blood donors and to detect the association of these variants on blood indices, and serum hepcidin/ferritin levels. Real-Time TaqMan genotyping assay for the specified variants was applied for 197 unrelated blood donors. Complete blood picture and serum hepcidin/ferritin levels were assessed. All participants were carriers of rs1800562*G/G genotype for HFE. The frequency of A/A and A/G genotypes of TMPRSS6 rs855791 variant was 55% and 45%, and for C/C, C/T, and T/T of BTBD9 rs9357271, were 15%, 43%, and 42%, respectively. Minor allele frequencies of rs855791*G and rs9357271*C were 0.23 and 0.37. The GGC genotype combination (for HFE/TMPRSS6/BTBD9, respectively) was more frequent in male participants. Higher serum hepcidin and hepcidin/ferritin ratio were observed in TMPRSS6 (A/G) carriers. While subjects with BTBD9 C/T and TT genotypes had lower serum ferritin values and higher levels of hepcidin and hepcidin/ferritin ratio compared with C/C genotype. No significant associations were found with any other blood parameters.In conclusion, TMPRSS6 rs855791 (A/G) and BTBD9 rs9357271 (C/T) variants were prevalent in the present blood donor population and may influence the serum hepcidin and/or ferritin levels.     

LRP6 downregulation promotes cardiomyocyte proliferation and heart regeneration

The adult mammalian heart is thought to be a terminally differentiated organ given the postmitotic nature of cardiomyocytes. Consequently, the potential for cardiac repair through cardiomyocyte proliferation is extremely limited. Low-density lipoprotein receptor-related protein 6 (LRP6) is a Wnt co-receptor that is required for embryonic heart development. In this study we investigated the role of LRP6 in heart repair through regulation of cardiomyocyte proliferation. Lrp6 deficiency increased cardiomyocyte cell cycle activity in neonatal, juvenile and adult mice. Cardiomyocyte-specific deletion of Lrp6 in the mouse heart induced a robust regenerative response after myocardial infarction (MI), led to reduced MI area and improvement in left ventricular systolic function. In vivo genetic lineage tracing revealed that the newly formed cardiomyocytes in Lrp6-deficient mouse hearts after MI were mainly derived from resident cardiomyocytes. Furthermore, we found that the pro-proliferative effect of Lrp6 deficiency was mediated by the ING5/P21 signaling pathway. Gene therapy using the adeno-associated virus (AAV)9 miRNAi-Lrp6 construct promoted the repair of heart injury in mice. Lrp6 deficiency also induced the proliferation of human induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs). Our study identifies LRP6 as a critical regulator of cardiomyocyte proliferation, which may lead to the development of a novel molecular strategy to promote myocardial regeneration and repair.Subject terms: Cell-cycle exit, Cytokinesis