Obesity and chronic liver disease nowadays affect about 30% of the population, especially in western countries, tendency rising, already putting health systems under extreme pressure. A sedentary lifestyle combined with a surplus of calories can lead to widespread changes throughout the body, including excessive expansion of adipose tissue, inflammatory processes, disturbances in glucose and insulin signaling, steatotic liver and cardiovascular diseases, and even certain types of cancer. Despite the severity of metabolic diseases, their pharmaceutical treatments are still limited, highlighting the ever increasing importance of research in this field. Chronic liver diseases are often associated with increased levels of programmed cell death such as apoptosis (non-immunogenic) and necroptosis (immunogenic). Studies could show, that effector proteins of necroptosis show upregulation in patients suffering from MASH, suggesting active involvement of necroptosis in the progression of MASLD. Animal studies that were using KO models of necroptosis executer MLKL were showing ambiguous results. While some claimed that MLKL deletion protects animals from diet-induced body weight gain, liver steatosis and insulin resistance, others could not see any protection at all. Due to indecisive literature, we decided to apply a novel MLKL point mutation (K219R), which expresses a full-length MLKL protein, while fully blocking its oligomerization, and thereby, necroptosis execution. We further applied three different feeding cohorts to animals: high caloric western diet alone (MASH) or in combination with alcohol (MetALD) as well as a control diet (NCD).While we could not observe a complete rescue in MLKL (K219R) animals from diet- and alcohol-induced changes, we show significant improvements of metabolic markers in these animals when compared to controls. These improvements are reflected by reduced body weight gain and adipose tissue mass, decreased levels of liver steatosis as well as liver damage associated serum markers. We could show mild effects on lipid metabolism in MLKL (K219R) livers, and we were able to show significantly reduced inflammation in epididymal adipose tissue as well as reduced differentiation potential of primary adipocytes from inguinal adipose tissue. Furthermore, animals on control diet did not show any spontaneous phenotype differences when compared to WT animals, but they displayed increased physical activity, potentially suggesting higher energy expenditure of MLKL (K219R) animals. By applying another point mutation to the upstream kinase and activator of necroptosis, RIPK1, we failed to observe any protective effects on diet-induced metabolic changes, suggesting that MLKL acts independent of RIPK1. Due to the fact, that we were not able to detect the phosphorylated form of MLKL, we suggest, that MLKL, in a metabolic context, acts cell-type specific as well as independent of necroptosis and its upstream kinases RIPK1/3. Consequently, this study makes a significant contribution to the ongoing scientific discourse around MLKL and its role in metabolic processes.
Michael Thaddäus Singer (Thu,) studied this question.