Liver fibrosis: causes and mechanisms
Liver fibrosis is a pathological condition characterized by excessive accumulation of scar tissue in the liver, which can lead to liver failure and cirrhosis. This condition is a consequence of various factors, including chronic infections, excessive alcohol consumption, and parasitic diseases such as schistosomiasis. Recently, research has highlighted a crucial role of autophagy in hepatic progenitor cells (HPCs) in the regulation of liver fibrosis. In particular, it has been found that autophagy in HPCs can modulate microRNAs (miRNAs) carried by exosomes, thereby influencing cellular processes that lead to fibrosis. This article will explore in detail the role of autophagy in HPCs, the mechanism of modulation by exosomal miRNAs, and the potential therapeutic implications of these findings for the prevention and treatment of liver fibrosis.
Schistosomiasis and its impact on the liver
Schistosomiasis is a parasitic disease caused by parasites of the genus Schistosoma, which affects millions of people in developing countries. The chronic form of the disease can lead to severe liver damage, including hepatic fibrosis, which is a pathological response to prolonged infection. Liver damage in schistosomiasis is largely due to the host’s inflammatory response to Schistosoma egg deposits in the liver. This inflammatory response causes activation of hepatic stellate cells (HSCs), which in turn produce excessive amounts of extracellular matrix, leading to fibrosis. Liver fibrosis can progress to cirrhosis, which increases the risk of hepatocellular carcinoma and end-stage liver failure, both life-threatening conditions.
Role of hepatic progenitor cells (HPCs) in liver regeneration
Hepatic progenitor cells (HPCs) are a population of stem cells present in the liver, with the ability to differentiate into both hepatocytes and bile duct cells. These cells play a key role in liver regeneration, especially in conditions of chronic liver injury. In response to liver injury, HPCs are activated and differentiate to repair damaged tissue. However, in a context of chronic inflammation, such as in schistosomiasis, the regenerative function of HPCs can be compromised. HPCs can interact with HSCs and other cells in the liver microenvironment, influencing fibrotic processes. The balance between tissue regeneration and fibrosis is crucial for liver health.
Autophagy: a pivotal cellular mechanism
Autophagy is an evolutionarily conserved catabolic process by which cells degrade and recycle damaged or unused cytoplasmic components. This process is essential for maintaining cellular homeostasis and responding to cellular stresses such as nutrient starvation or accumulation of misfolded proteins. Autophagy can be nonselective, involving the degradation of random portions of the cytoplasm, or selective, in which specific organelles or proteins are targeted for degradation. Autophagy protects cells from cellular damage and promotes cell survival under stressful conditions. It also regulates inflammation and immune response, two processes closely linked to liver fibrosis.
Autophagy in hepatic progenitor cells
In HPCs, autophagy plays a crucial role in maintaining their regenerative capacity and modulating interactions with the liver microenvironment. Autophagy in HPCs is essential for maintaining their stem cell-like properties and their ability to differentiate into mature liver cells. Through regulation of autophagy, HPCs may influence the progression of liver fibrosis by modulating the secretion of pro-fibrotic and anti-inflammatory factors.
Exosomes and microRNAs: messengers in cellular communication
Exosomes are small extracellular vesicles, released by multiple cell types, that transport proteins, lipids and RNA, including microRNAs (miRNAs). These vesicles play a fundamental role in intercellular communication, influencing the behavior of recipient cells. Exosomes are formed inside cells as intraluminal vesicles, which are then released into the extracellular microenvironment. They can be taken up by neighboring cells or transported remotely through the bloodstream. Through the transport of miRNAs and other molecules, exosomes can modulate various cellular processes, including proliferation, differentiation and immune response.
microRNAs and regulation of fibrosis
MicroRNAs are small non-coding RNA molecules that regulate gene expression at the post-transcriptional level. In recent years, miRNAs have received increasing attention for their role in regulating liver fibrosis. Some miRNAs can inhibit liver fibrosis by regulating the expression of genes involved in extracellular matrix production or HSC activation. Other miRNAs, on the contrary, can promote fibrosis by increasing the expression of pro-fibrotic factors or promoting inflammation. The study conducted on autophagy in HPCs revealed that this process can modulate the miRNA content in exosomes released by HPCs.
This modulation can have significant effects on the progression of liver fibrosis. Autophagy can influence which miRNAs are encapsulated in exosomes. For example, induction of autophagy can promote the loading of anti-fibrotic miRNAs into exosomes, while its inhibition could favor pro-fibrotic miRNAs. Exosomes released by HPCs under the influence of autophagy can modulate HSC activation, reducing or promoting extracellular matrix production and fibrosis progression.
Implications for liver fibrosis therapy
The findings on the modulation of exosomes by autophagy in HPCs open new perspectives for the development of innovative therapies for liver fibrosis. Exosomes designed to carry specific antifibrotic miRNAs could be used as a therapy to inhibit liver fibrosis. These exosomes could be administered systemically or locally to the liver. Modulation of autophagy in HPCs by drugs or other therapies could represent a strategy to control the release of therapeutic exosomes and thus regulate liver fibrosis. There are both natural and synthetic inducers of autophagy: among the former is lipoic acid, a vitamin-like compound that is an antioxidant and regularly required for liver cell functions.
Berberine and other alkaloids isolated from echinacea, barberry and phellodendron also have this ability. Foods such as beets contain betalains, which in addition to their antioxidant action can induce autophagy as demonstrated in tumor cells in culture. Finally, spices such as parsley, sage, turmeric and cardamom contain aromatic terpenes with the same properties. With further research and development, these discoveries could lead to therapeutic innovations that will revolutionize the management of liver fibrosis and other chronic liver diseases.
- Edited by Dr. Gianfrancesco Cormaci, PhD, specialist in Clinical Biochemistry.
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