Things that go BMP in the liver: bone morphogenetic protein 6 and the control of body iron homeostasis

Hepatitis B Virus-Associated Liver Carcinoma: The Role of Iron Metabolism and Its Modulation

Hepatitis B virus (HBV) infection is a significant contributor to the development of hepatocellular carcinoma (HCC), a leading cause of cancer-related mortality worldwide. Iron, a central co-factor in various metabolic pathways, plays an essential role in liver function, but its dysregulation can lead to severe health consequences. Accumulation of iron within hepatic cells over time is linked to increased liver injury and is strongly associated with sensitive exposure to a range of conditions, including cirrhosis, fibrosis and ultimately, HCC. This review explores the intricate interplay between iron metabolism and HCC within the context of HBV infection. Hepatic iron overload can arise from liver injury and disruptions in iron homeostasis, causing hepatic necrosis, inflammation, and fibrosis, ultimately culminating in carcinogenesis. Moreover, alterations in serum iron components in HBV-related scenarios have been observed to impact the persistence of HBV infection. Notably, the progression of HBV-associated liver damage exhibits distinct characteristics at various stages of liver disease. In addition to elucidating the complex relationship between iron metabolism and HCC in the context of HBV infection, this review also investigates the prognostic implications of systemic iron levels for HCC. Furthermore, it aims to provide a comprehensive understanding of the intricate interplay between iron metabolism and HCC, extending the discussion to the context of hepatitis C virus (HCV) infection. By shedding light on these multifaceted connections, this review aims to contribute to our understanding of the pathogenesis of HBV-associated HCC and potentially identify novel therapeutic avenues for intervention.

Macrophages in Bone Homeostasis

Aberrant or prolonged immune responses has been proved to be involved in bone homeostasis. As a component of the innate immune system, macrophages play a critical role in bone homeostasis. Conventionally, according to response to the various panel of stimuli, macrophages can be plastically classified into two major phenotypes: M1 and M2. M1 macrophages are generally proinflammatory, whereas M2 are anti-inflammatory. Although studies demonstrated that both M1 and M2 phenotypes have been implicated in various inflammatory bone diseases, their direct role in bone homeostasis remains unclear. Thus, in this review, we briefly discuss the term "osteoimmunology", which deals with the crosstalk and shared mechanisms of the bone and immune systems. In addition, we overview M1 and M2 macrophages for their role in osteoclastogenesis and osteogenesis as well as relevant signaling cascades involved.

Abnormal serum iron markers in chronic hepatitis B virus infection may be because of liver injury

OBJECTIVE

In patients with chronic hepatitis B virus (HBV) infection, it is not known whether altered serum iron markers are directly because of the infection or the associated liver injury. We determined the serum iron status of patients with chronic HBV infection, and investigated whether it is HBV infection or HBV-related liver injury that likely causes abnormal serum iron markers in chronic HBV infection.

MATERIALS AND METHODS

For a retrospective study, chronic HBV-infected patients (80 patients with cirrhosis and 76 patients without cirrhosis) and 58 healthy controls were enrolled. Serum alanine transaminase levels were measured to ascertain liver damage. Indicators of iron status included serum iron, ferritin, and transferrin.

RESULTS

Compared with noncirrhotic patients and healthy controls, the serum transferrin of cirrhotic patients was lower and the serum iron and ferritin values were higher (P < 0.001, all). In cirrhotic patients, the serum iron and ferritin levels correlated positively with serum alanine transaminase levels and the transferrin levels were inversely related to both end-stage liver disease scores and iron levels (all P < 0.01).

CONCLUSION

Serum iron markers tended to be aberrant in chronic HBV-infected patients with cirrhosis. The liver injury associated with HBV infection, but not chronic HBV infection directly, is likely the main cause for iron metabolism disorder.

Bone morphogenetic proteins as regulators of iron metabolism

Bone morphogenetic proteins (BMPs) are members of the transforming growth factor-beta (TGF-β) superfamily of signaling molecules. In addition to protean roles in embryonic development, germ-line specification, and cellular differentiation, a central role in iron homeostasis has recently been demonstrated for certain BMPs. Specifically, BMP6 serves to relate hepatic iron stores to the hepatocellular expression of the iron-regulatory hormone hepcidin. This regulation occurs via cellular SMAD-signaling molecules and is strongly modulated by the BMP coreceptor hemojuvelin (HJV). Mutations in certain genes influencing signaling to hepcidin via the BMP/SMAD pathway are associated with human disorders of iron metabolism, such as hereditary hemochromatosis and iron-refractory iron-deficiency anemia. Evidence suggests that signals in addition to iron stores influence hepcidin expression via the BMP/SMAD pathway. This review summarizes the details of BMP/SMAD signaling, with a particular focus on its role in iron homeostasis and iron-related diseases.