https://www.gastrojournal.org/article/S0016-5085(08)00429-0/pdf

Mechanisms of Hepatic Fibrogenesis

The hepatic stellate cell has surprised and engaged physiologists, pathologists, and hepatologists for over 130 years, yet clear evidence of its role in hepatic injury and fibrosis only emerged following the refinement of methods for its isolation and characterization. The paradigm in liver injury of activation of quiescent vitamin A-rich stellate cells into proliferative, contractile, and fibrogenic myofibroblasts has launched an era of astonishing progress in understanding the mechanistic basis of hepatic fibrosis progression and regression. But this simple paradigm has now yielded to a remarkably broad appreciation of the cell's functions not only in liver injury, but also in hepatic development, regeneration, xenobiotic responses, intermediary metabolism, and immunoregulation. Among the most exciting prospects is that stellate cells are essential for hepatic progenitor cell amplification and differentiation. Equally intriguing is the remarkable plasticity of stellate cells, not only in their variable intermediate filament phenotype, but also in their functions. Stellate cells can be viewed as the nexus in a complex sinusoidal milieu that requires tightly regulated autocrine and paracrine cross-talk, rapid responses to evolving extracellular matrix content, and exquisite responsiveness to the metabolic needs imposed by liver growth and repair. Moreover, roles vital to systemic homeostasis include their storage and mobilization of retinoids, their emerging capacity for antigen presentation and induction of tolerance, as well as their emerging relationship to bone marrow-derived cells. As interest in this cell type intensifies, more surprises and mysteries are sure to unfold that will ultimately benefit our understanding of liver physiology and the diagnosis and treatment of liver disease.

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Hepatic Stellate Cells: Protean, Multifunctional, and Enigmatic Cells of the Liver

Molecular regulation of hepatic fibrosis, an integrated cellular response to tissue injury.

Hepatic fibrosis is a common response to chronic liver injury from many causes, including alcohol, persistent viral and helminthic infections, and hereditary metal overload. Emerging evidence suggests that cellular mechanisms of hepatic fibrosis are shared among these different insults and, moreover, that the liver's response is a paradigm for parenchymal wound healing in other tissues. Advances in the isolation and characterization of liver cells, in conjunction with progress in matrix and cytokine biology, have led to important new insights about the cellular basis of hepatic fibrosis. In particular, the hepatic lipocyte (also known as the stellate, fat-storing, perisinusoidal, or Ito . . .

The Cellular Basis of Hepatic Fibrosis -- Mechanisms and Treatment Strategies

Background In patients with cirrhosis and spontaneous bacterial peritonitis, renal function frequently becomes impaired. This impairment is probably related to a reduction in effective arterial blood volume and is associated with a high mortality rate. We conducted a study to determine whether plasma volume expansion with intravenous albumin prevents renal impairment and reduces mortality in these patients. Methods We randomly assigned 126 patients with cirrhosis and spontaneous bacterial peritonitis to treatment with intravenous cefotaxime (63 patients) or cefotaxime and intravenous albumin (63 patients). Cefotaxime was given daily in doses that varied according to the serum creatinine level, and albumin was given at a dose of 1.5 g per kilogram of body weight at the time of diagnosis, followed by 1 g per kilogram on day 3. Renal impairment was defined as nonreversible deterioration of renal function during hospitalization. Results The infection resolved in 59 patients in the cefotaxime group (94 percent...

https://www.nejm.org/doi/pdf/10.1056/NEJM199908053410603

Effect of Intravenous Albumin on Renal Impairment and Mortality in Patients with Cirrhosis and Spontaneous Bacterial Peritonitis

https://www.gastrojournal.org/article/S0016-5085(96)00086-8/pdf

Endothelin 1 is overexpressed in human cirrhotic liver and exerts multiple effects on activated hepatic stellate cells

Liver perisinusoidal fat-storing cells (FSC) show morphological and ultrastructural characteristics similar to pericytes regulating local blood flow in other organs. In the present study we have analyzed whether FSC respond to local vasoconstrictors such as thrombin, angiotensin-II, and endothelin-1 with an increase in intracellular free calcium concentration ([Ca2+]i) coupled with effective cell contraction. All agonists tested induced a rapid and dose-dependent increase in [Ca2+]i followed by a sustained phase lasting several minutes in confluent monolayers of Fura-2-loaded human FSC. Pharmacological studies performed using different Ca2+ channel blockers indicated that, at least for thrombin and angiotensin-II, the sustained phase is due to the opening of voltage-sensitive membrane Ca2+ channels. To analyze the temporal and spatial dynamics of Ca2+ release in response to these agonists, we performed experiments on individual Fura-2-loaded human FSC using a dual wavelength, radiometric video imaging system. The rise in [Ca2+]i was exclusively localized to the cytoplasm, particularly in the branching processes. Increases in [Ca2+]i more than four-fold were associated with a simultaneous and transient reduction of cell area indicating reversible cell contraction. Our results indicate that the Ca(2+)-dependent contraction of human FSC in vitro may reflect a potential role in regulating sinusoidal blood flow in vivo.

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Fat-storing cells as liver-specific pericytes. Spatial dynamics of agonist-stimulated intracellular calcium transients.

Liver perisinusoidal fat-storing cells (FSC) show morphological and ultrastructural characteristics similar to pericytes regulating local blood flow in other organs. In the present study we have analyzed whether FSC respond to local vasoconstrictors such as thrombin, angiotensin-II, and endothelin-1 with an increase in intracellular free calcium concentration (ICa2I1I) coupled with effective cell contraction. All agonists tested induced a rapid and dose-dependent increase in ICa2`i1 followed by a sustained phase lasting several minutes in confluent monolayers of Fura-2-loaded human FSC. Pharmacological studies performed using different Ca2+ channel blockers indicated that, at least for thrombin and angiotensin-II, the sustained phase is due to the opening of voltage-sensitive membrane Ca2" channels. To analyze the temporal and spatial dynamics of Ca2" release in response to these agonists, we performed experiments on individual Fura-2-loaded human FSC using a dual wavelength, ratiometric video imaging system. The rise in ICa2"], was exclusively localized to the cytoplasm, particularly in the branching processes. Increases in ICa2"1, more than fourfold were associated with a simultaneous and transient reduction of cell area indicating reversible cell contraction. Our results indicate that the Ca2"-dependent contraction of human FSC in vitro may reflect a potential role in regulating sinusoidal blood flow in vivo. (J. Clin. Invest. 1992. 90:642-646.) Key

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Spatial Dynamics of Agonist-stimulated Intracellular Calcium Transients

Platelet-derived growth factor (PDGF) is a key mitogen for hepatic stellate cells (HSC) and has been shown to be implicated in liver tissue repair and fibrogenesis. In this study the relationship between PDGF-induced intracellular Ca2+ concentration ([Ca2+]i) increase and mitogenesis in cultured human HSC was evaluated. In high-density cell cultures (80-90% subconfluence), PDGF induced a significant increase in [Ca2+]i, characterized by a short-lasting peak phase, which was followed by a long-lasting plateau phase. The plateau phase was abolished in the absence of extracellular Ca2+. However, in low-density cell cultures (30-40% subconfluence), the plateau phase was absent or markedly less pronounced. In parallel sets of experiments, PDGF was significantly less effective in inducing mitogenesis in low-density cell cultures than in high-density cell cultures and was totally ineffective in the absence of extracellular Ca2+. These results suggest that 1) spatial and time dynamics of PDGF-induced [Ca2+]i increase are dependent on cell density and 2) PDGF-induced mitogenesis requires extracellular Ca2+ influx.

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The mitogenic effect of platelet-derived growth factor in human hepatic stellate cells requires calcium influx

We investigated the effect of the NO-donor S-nitroso-N-acetyl-DL-penicillamine (SNAP) on cardiomyocytes isolated from control normotensive Wistar Kyoto (WKY) and spontaneously hypertensive (SHR) rats.




Ventricular cardiomyocytes were isolated from SHR and WKY hearts and imaging analysis of fura-2-loaded cells was performed in order to evaluate calcium transient in electrical field paced (0.5 Hz) cells.




In WKY cardiomyocytes, 1 – 200 μM SNAP dose-dependently increased cyclic GMP content. In basal conditions, cyclic GMP content of SHR cardiomyocytes was significantly higher than in WKY, but SNAP failed to further increase cyclic GMP over the basal level.




In control conditions, the ΔF/F and decay time of the calcium transient were similar in both strains. In WKY cardiomyocytes, SNAP (1 – 100 μM) reduced the decay time. In SHR cardiomyocytes, SNAP was ineffective. Dibutyryl cyclic GMP (10−6 – 10−8 M), a membrane permeable cyclic GMP analogue, behaved similarly to SNAP.




In WKY and SHR cardiomyocytes, 10−8 M isoprenaline similarly increased ΔF/F and decreased the decay time. SNAP and dibutyryl cyclic GMP prevented the effect of isoprenaline in WKY, whereas both molecules were ineffective in SHR cardiomyocytes. In WKY, SNAP effects were blocked by pretreating cells with the cGK inhibitor KT-5823.




Western blotting analysis of cGK type I showed that the enzyme was expressed in WKY isolated cardiomyocytes, but absent in four out of five SHR preparations.




We concluded that the low expression of cGKI may determine the lack of NO/cyclic GMP-dependent regulation on calcium transient in SHR cardiomyocytes. This alteration may contribute to the development of heart hypertrophy in hypertensive status.






British Journal of Pharmacology (2001) 134, 596–602; doi:10.1038/sj.bjp.0704275

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C. Ruocco

Papers

Endothelin 1 is overexpressed in human cirrhotic liver and exerts multiple effects on activated hepatic stellate cells

Fat-storing cells as liver-specific pericytes. Spatial dynamics of agonist-stimulated intracellular calcium transients.

Spatial Dynamics of Agonist-stimulated Intracellular Calcium Transients

The mitogenic effect of platelet-derived growth factor in human hepatic stellate cells requires calcium influx

Guanosine 3': 5'-cyclic monophosphate-dependent pathway alterations in ventricular cardiomyocytes of spontaneously hypertensive rats.