The effect of liver-specific ketohexokinase deletion on the intestinal-liver-kidney axis in high-fructose-induced metabolic syndrome mice

Abstract

The liver is a crucial site for fructose uptake and metabolism, a function intricately linked to fructose-associated pathologies. This study examines the role of hepatic ketohexokinase (KHK) in metabolic syndrome induced solely by high-fructose intake. Liver-specific Khk-deficient mice are generated and fed with a 20% fructose solution for 3 months, after which the features of metabolic syndrome are examined. Compared with fructose-fed floxed controls, fructose-fed liver-specific Khk-deficient mice present alleviated liver injury and hepatic steatosis, along with lower triglyceride levels in the plasma and liver, plasma aspartate transaminase and alanine transaminase levels, and mRNA levels of genes related to triglyceride and fatty acid synthesis. Liver-specific Khk deficiency also leads to lower uric acid levels in the plasma and urine, as well as xanthine oxidase activity and Glut9 mRNA levels in the liver and kidneys of fructose-fed mice. Although intestinal villus length and epithelial barrier integrity remain unaffected, the deletion of liver Khk significantly reduces fructose-stimulated KHK, Glut2, Glut5, and aldolase B expression in the intestine and kidneys, suggesting inhibited fructose absorption and metabolism in these tissues. In the adipose tissue, fructose-induced increases in adipocyte size and tumor necrosis factor-α and interleukin-6 mRNA levels are blocked by liver-specific Khk deficiency, indicating improved remodeling of adipose tissue and reduced inflammation in adipocytes. Overall, liver-specific Khk deletion is sufficient to protect against metabolic syndrome induced by excessive fructose intake. Our findings underscore the critical role of liver KHK-mediated fructose metabolism in driving the physiological and pathological consequences associated with fructose consumption along the intestinal-liver-kidney axis.

1. Introduction

Although dietary fructose is derived primarily from vegetables and fruits, the consumption of fructose in the form of sugar and high-fructose (HF) corn syrup, two major commercially added sweeteners, has increased dramatically over the past few decades. This rise coincides with a marked global increase in metabolic diseases, including metabolic dysfunction-associated steatotic liver disease [1]. In animal models, HF consumption has been shown to induce all the features of metabolic syndrome, such as weight gain, hepatic steatosis, fatty liver, glucose intolerance, hyperinsulinemia, and insulin resistance [2–4]. Similarly, robust evidence from human studies has revealed a strong association between the consumption of HF-containing beverages and the development of key metabolic syndrome components, including obesity, fatty liver, and insulin resistance [5,6].

Ketohexokinase (KHK, also known as fructokinase), an initial enzyme for fructose metabolism, catalyzes the phosphorylation of fructose to generate uric acid (UA) and fructose 1-phosphate. The latter is further converted by aldolase B (AldoB) into dihydroxyacetone phosphate and glyceraldehyde, precursors for triglyceride synthesis [7]. KHK exists in two isoforms: KHK-A, a slow-acting fructose metabolizer ubiquitously expressed across multiple tissues, and KHK-C, a rapid metabolizer primarily expressed in the liver, small intestine, and kidney [8]. Growing evidence from animal studies has implicated KHK-mediated fructose metabolism in the pathogenesis of fructose-related metabolic syndrome. Notably, in fructose-fed mice, systemic deficiency of KHK-A/C [9–13] or the administration of KHK-specific inhibitors (e.g., PF-06835919 [14–16] and compound 14 [17]) has been shown to significantly mitigate various metabolic syndrome phenotypes associated with fructose overconsumption. However, highlighting the divergent roles of KHK-A and KHK-C is critical: systemic deletion of Khk-a exacerbated, whereas global knockout of Khk-c improved, fructose-induced metabolic syndrome in murine models [10,18]. Collectively, these findings consistently support the targeting of KHK as a promising therapeutic strategy for fructose-induced metabolic syndrome.

In the liver, fructose is primarily transported via glucose transporter (GLUT) 2 from the portal circulation into hepatocytes [19], where KHK and AldoB sequentially metabolize fructose to generate UA and triglycerides [7]. Notably, liver-specific Khk knockdown via N-acetylgalactosamine (GalNAc)-conjugated Khk siRNA significantly improved glucose tolerance and attenuated hepatic steatosis in mice fed with a high-fat diet with [20] or without [16] fructose drinking, providing direct evidence for the critical role of hepatic KHK in the development of fructose-related metabolic syndrome. This conclusion was further corroborated by studies from Andres-Hernando et al., which demonstrated that liver-specific KHK-A/C deficiency...