Effects of Long-Term Exercise on Liver Cyst in Polycystic Liver Disease Model Rats

Polycystic liver diseases: from molecular basis to development of effective treatments

Polycystic liver diseases (PLDs) comprise a heterogeneous group of congenital genetic disorders that mainly affect bile duct epithelial cells, known as cholangiocytes. Patients with PLD usually present bile duct dilatation and/or progressive develop intrahepatic, fluid-filled biliary cysts (more than 10), which is the main cause of morbidity.

Genetics, pathobiology and therapeutic opportunities of polycystic liver disease

Polycystic liver diseases (PLDs) are inherited genetic disorders characterized by progressive development of intrahepatic, fluid-filled biliary cysts (more than ten), which constitute the main cause of morbidity and markedly affect the quality of life. Liver cysts arise in patients with autosomal dominant PLD (ADPLD) or in co-occurrence with renal cysts in patients with autosomal dominant or autosomal recessive polycystic kidney disease (ADPKD and ARPKD, respectively). Hepatic cystogenesis is a heterogeneous process, with several risk factors increasing the odds of developing larger cysts. Depending on the causative gene, PLDs can arise exclusively in the liver or in parallel with renal cysts. Current therapeutic strategies, mainly based on surgical procedures and/or chronic administration of somatostatin analogues, show modest benefits, with liver transplantation as the only potentially curative option. Increasing research has shed light on the genetic landscape of PLDs and consequent cholangiocyte abnormalities, which can pave the way for discovering new targets for therapy and the design of novel potential treatments for patients. Herein, we provide a critical and comprehensive overview of the latest advances in the field of PLDs, mainly focusing on genetics, pathobiology, risk factors and next-generation therapeutic strategies, highlighting future directions in basic, translational and clinical research.

Chronic Exercise Protects against the Progression of Renal Cyst Growth and Dysfunction in Rats with Polycystic Kidney Disease

Introduction

Polycystic kidney disease (PKD) is a genetic disorder characterized by the progressive enlargement of renal epithelial cysts and renal dysfunction. Previous studies have reported the beneficial effects of chronic exercise on chronic kidney disease. However, the effects of chronic exercise have not been fully examined in PKD patients or models. The effects of chronic exercise on the progression of PKD were investigated in a polycystic kidney (PCK) rat model.

Methods

Six-week-old male PCK rats were divided into a sedentary group and an exercise group. The exercise group underwent forced treadmill exercise for 12 wk (28 m·min⁻¹, 60 min·d⁻¹, 5 d·wk⁻¹). After 12 wk, renal function and histology were examined, and signaling cascades of PKD progression, including arginine vasopressin (AVP), were investigated.

Results

Chronic exercise reduced the excretion of urinary protein, liver-type fatty acid–binding protein, plasma creatinine, urea nitrogen, and increased plasma irisin and urinary AVP excretion. Chronic exercise also slowed renal cyst growth, glomerular damage, and interstitial fibrosis and led to reduced Ki-67 expression. Chronic exercise had no effect on cAMP content but decreased the renal expression of B-Raf and reduced the phosphorylation of extracellular signal-regulated kinase (ERK), mammalian target of rapamycin (mTOR), and S6.

Conclusion

Chronic exercise slows renal cyst growth and damage in PCK rats, despite increasing AVP, with the downregulation of the cAMP/B-Raf/ERK and mTOR/S6 pathways in the kidney of PCK rats.

Metformin slows liver cyst formation and fibrosis in experimental model of polycystic liver disease

Polycystic liver disease (PLD) is a hereditary liver disease in which the number of cysts increases over time, causing various abdominal symptoms and poor quality of life. Although effective treatment for PLD has not been established, we recently reported that long-term exercise ameliorated liver cyst formation and fibrosis with the activation of AMP-activated protein kinase (AMPK) in polycystic kidney (PCK) rats, a PLD model. Therefore, the aim of this study was to investigate whether metformin, an indirect AMPK activator, was effective in PCK rats. PCK rats were randomly divided into a control (Con) group and a metformin-treated (Met) group. The Met group was treated orally with metformin in drinking water. After 12 wk, liver function, histology, and signaling cascades of PLD were examined in the groups. Metformin did not affect the body weight or liver weight, but it reduced liver cyst formation, cholangiocyte proliferation, and fibrosis around the cyst. Metformin increased the phosphorylation of AMPK and tuberous sclerosis complex 2 and decreased the phosphorylation of mammalian target of rapamycin, S6, and extracellular signal-regulated kinase and the expression of cystic fibrosis transmembrane conductance regulator, aquaporin I, transforming growth factor-β, and type 1 collagen without changes in apoptosis or collagen degradation factors in the liver. Metformin slows the development of cyst formation and fibrosis with the activation of AMPK and inhibition of signaling cascades responsible for cellular proliferation and fibrosis in the liver of PCK rats.NEW & NOTEWORTHY This study indicates that metformin, an indirect AMPK activator slows liver cyst formation and fibrosis in PLD rat model. Metformin attenuates excessive cell proliferation in the liver with the inactivation of mTOR and ERK pathways. Metformin also reduces the expression of proteins responsible for cystic fluid secretion and liver fibrosis. Metformin and AMPK activators may be potent drugs for polycystic liver disease.

Exercise combined with a probiotics treatment alters the microbiome, but moderately affects signalling pathways in the liver of male APP/PS1 transgenic mice

It has been demonstrated that physical exercise and probiotic supplementation delay the progress of Alzheimer's Disease (AD) in male APP/PS1^TG mice. However, it has also been suggested that both exercise and AD have systemic effects. We have studied the effects of exercise training and probiotic treatment on microbiome and biochemical signalling proteins in the liver. The results suggest that liver is under oxidative stress, since SOD2 levels of APP/PS1 mice were decreased when compared to a wild type of mice. Exercise training prevented this decrease. We did not find significant changes in COX4, SIRT3, PGC-1a or GLUT4 levels, while the changes in pAMPK/AMPK, pmTOR/mTOR, pS6/S6 and NRF2 levels were randomly modulated. The data suggest that exercise and probiotics-induced changes in microbiome do not strongly affect mitochondrial density or protein synthesis-related AMPK/mTOR/S6 pathways in the liver of these animals.