In addition to liver-resident Kupffer cells, infiltrating immune cells have recently been linked to the development of liver fibrosis. Blood monocytes are circulating precursors of tissue macrophages and can be divided into two functionally distinct subpopulations in mice: Gr1^hi (Ly6C^hi) and Gr1^lo (Ly6C^lo) monocytes. The role of these monocyte subsets in hepatic fibrosis and the mechanisms of their differential recruitment into the injured liver are unknown. We therefore characterized subpopulations of infiltrating monocytes in acute and chronic carbon tetrachloride (CCl₄)-induced liver injury in mice using flow cytometry and immunohistochemistry. Inflammatory Gr1^hi but not Gr1^lo monocytes are massively recruited into the liver upon toxic injury constituting an up to 10-fold increase in CD11b⁺F4/80⁺ intrahepatic macrophages. Comparing wild-type with C-C chemokine receptor (CCR2)-deficient and CCR2/CCR6–deficient mice revealed that CCR2 critically controls intrahepatic Gr1^hi monocyte accumulation by mediating their egress from bone marrow. During chronic liver damage, intrahepatic CD11b⁺F4/80⁺Gr1⁺ monocyte-derived cells differentiate preferentially into inducible nitric oxide synthase–producing macrophages exerting proinflammatory and profibrogenic actions, such as promoting hepatic stellate cell (HSC) activation, T helper 1–T cell differentiation and transforming growth factor β (TGF-β) release. Impaired monocyte subset recruitment in Ccr2 ^−/− and Ccr2 ^−/− Ccr6 ^−/− mice results in reduced HSC activation and diminished liver fibrosis. Moreover, adoptively transferred Gr1^hi monocytes traffic into the injured liver and promote fibrosis progression in wild-type and Ccr2 ^−/− Ccr6 ^−/− mice, which are otherwise protected from hepatic fibrosis. Intrahepatic CD11b⁺F4/80⁺Gr1⁺ monocyte-derived macrophages purified from CCl₄-treated animals, but not naïve bone marrow monocytes or control lymphocytes, directly activate HSCs in a TGF-β–dependent manner in vitro. Conclusion: Inflammatory Gr1⁺ monocytes, recruited into the injured liver via CCR2-dependent bone marrow egress, promote the progression of liver fibrosis. Thus, they may represent an interesting novel target for antifibrotic strategies. (Hepatology 2009;50:261–274.)

Hepatic fibrosis is a scarring process that is associated with an increased and altered deposition of extracellular matrix in liver. At the cellular and molecular level, this progressive process is mainly characterized by cellular activation of hepatic stellate cells and aberrant activity of transforming growth factor‐β1 and its downstream cellular mediators. Although the cellular responses to this cytokine are complex, the signalling pathways of this pivotal cytokine during the fibrogenic response and its connection to other signal cascades are now understood in some detail. Based on the current advances in understanding the pleiotropic reactions during fibrogenesis, various inhibitors of transforming growth factor‐β were developed and are now being investigated as potential drug candidates in experimental models of hepatic injury. Although it is too early to favour one of these antagonists for the treatment of hepatic fibrogenesis in human, the experimental results obtained yet provide stimulatory impulses for the development of an effective treatment of choice in the not too distant future. The present review summarises the actual knowledge on the pathogenesis of hepatic fibrogenesis, the role of transforming growth factor‐β and its signalling pathways in promoting the fibrogenic response, and the therapeutic modalities that are presently in the spotlight of many investigations and are already on the way to take the plunge into clinical studies.

Obesity or excessive weight gain is identified as the most important and significant risk factor in the development and progression of type 2 diabetes mellitus (DM) in all age groups. It has reached pandemic dimensions, making the treatment of obesity crucial in the prevention and management of type 2 DM worldwide. Multiple clinical studies have demonstrated that moderate and sustained weight loss can improve blood glucose levels, insulin action and reduce the need for diabetic medications. A combined approach of diet, exercise and lifestyle modifications can successfully reduce obesity and subsequently ameliorate the ill effects and deadly complications of DM. This approach also helps largely in the prevention, control and remission of DM. Obesity and DM are chronic diseases that are increasing globally, requiring new approaches to manage and prevent diabetes in obese individuals. Therefore, it is essential to understand the mechanistic link between the two and design a comprehensive approach to increase life expectancy and improve the quality of life in patients with type 2 DM and obesity. This literature review provides explicit information on the clinical definitions of obesity and type 2 DM, the incidence and prevalence of type 2 DM in obese individuals, the indispensable role of obesity in the pathophysiology of type 2 DM and their mechanistic link. It also discusses clinical studies and outlines the recent management approaches for the treatment of these associated conditions. Additionally, in vivo studies on obesity and type 2 DM are discussed here as they pave the way for more rigorous development of therapeutic approaches.

TGF-beta has multiple profibrogenic but also anti-inflammatory and immunosuppressive effects. The balance of these actions is required for maintaining tissue homeostasis and an aberrant expression of TGF-beta is involved in a number of disease processes in the liver. In addition to its fibrogenic action leading to transdifferentiation of hepatic stellate cells into myofibroblasts, TGF-beta is also an important negative regulator of proliferation and an inducer of apoptosis. The major portion of TGF-beta is secreted as part of an inactive complex and the details of the activation process in liver have not yet been elucidated. The initially striking simplicity of the core TGF-beta/Smad signaling pathways is rapidly giving way to a much more complex view of intracellular signal transduction mechanisms and recent work has demonstrated the importance of cross-talk among different signaling pathways to either specify, enhance, or inhibit TGF-beta responses. The ubiquitous pathophysiologic relevance of TGF-beta suggests its measurement in blood as a diagnostic tool. Other strategies aim at inhibition of TGF-beta1 function or synthesis as a primary target for the development of antifibrotic strategies and recent advances in cell biology have opened several ways to approach the inhibition of TGF-beta action.