Periodic Reporting for period 3 - NEUMACS (Neuron-associated macrophages in the gut as novel target for the treatment of enteric neuropathies)
Okres sprawozdawczy: 2022-10-01 do 2024-03-31
The gastrointestinal tract has the vital task to digest and absorb ingested food, a complex process requiring coordinated integration of motility, secretion, vascularization and absorption. Thereto the gastrointestinal tract is equipped with its own nervous system, the enteric nervous system (ENS), capable of controlling gut function independently of input from brain or spinal cord. Reduction in number or dysfunction of the neurons within the gut wall, also referred to as enteric neuropathy, significantly impacts on gut function, resulting in stasis of luminal contents and malabsorption, chronic pain, vomiting, bloating and severe constipation. Enteric neuropathies are common in prevalent disorders such as obesity, diabetes, and ageing, all major contributors to the health burden. Despite the continuous global increase in incidence of these disorders, the insight in the mechanisms leading to the reduction or dysfunction of enteric neurons is limited and most importantly, adequate treatment is lacking. Recently, we collected evidence that survival of enteric neurons is guaranteed by a unique subpopulation of resident macrophages closely associated to the ENS and expressing a typical neuroprotective / -supportive transcriptome. In line, depletion of these neuron-associated macrophages (NA-MF) results in apoptosis and a reduction in number of enteric neurons leading to severely impaired gastrointestinal motility. We pose the provocative hypothesis that enteric neuropathy results from impaired support to the ENS by NA-MF, leading to neural distress and apoptosis. Using state-of-the-art methods, we will first characterize in depth the NA-MF population to subsequently unravel the mechanisms leading to failure of NA-MF to support and protect the ENS in animal models and in patients. These ground-breaking insights will allow us to identify therapeutic targets for the treatment of enteric neuropathies, representing an exponentially growing health problem of the 21st century.
In the past 2 ½ years, we have focused on further identifying and characterizing the macrophage population that closely interacts with the enteric nervous system both in mice and humans. In mice, we were able to demonstrate that macrophages have a key role in shaping the enteric nervous prior to weaning. We showed that macrophages prune synapses and phagocytose abundant neurons required to obtain the typical organization of enteric neurons into ganglia. Depletion of macrophages prior to weaning indeed results in disorganization of enteric neurons with absence of the typical ganglia. After weaning, we showed that macrophages differentiate into different subtypes including neuron-associated macrophages (NA-MF). We discovered that neurons secrete a mediator that instructs surrounding macrophages to obtain neuron-protective properties, information that might be important to develop new treatments for neurodegeneration of the enteric nervous system. Next, we embarked on experiments studying NA-MF function in three different models of neurodegeneration, i.e. aging, diabetes and obesity. In parallel to the preclinical studies, we have collected human colon samples and studied the macrophage subpopulations in the three different layers of the gut. We are currently close to identifying the NA-MF in humans and to select specific membrane markers allowing us to isolate and study these NA-MF in more detail in conditions of neurodegeneration, such as constipation and aging. Finally, to validate targets or pathways involved in neurodegeneration, we have developed a co-culture platform consisting of macrophages and enteric neurons derived from human pluripotent stem cells. The pluripotent stem cells can indeed be matured into enteric neurons which seem to instruct monocytes into macrophages that are closely associated to the neurons. This platform is currently validated and further optimized and will provide invaluable information on the interaction between these two cell populations.
Unexpectedly we identified a new role for intestinal macrophages, namely that early in life, they are key players in the maturation of the enteric nervous system. Moreover, in collaboration with our colleagues from hepatology, we further explored the role of another subpopulation of macrophages of which we previously demonstrated to be long-lived and involved in the maintenance of blood vessel integrity. Using the know-how obtained in the past few years, we have collected interesting novel insights in the role of these blood vessel associated macrophages in bacterial translocation in a mouse model of liver disease. This work is groundbreaking and will have a major impact on our understanding of liver disease.
In the coming years, we expect to identify the human NA-MF subpopulation in great detail and to uncover their role in enteric neurodegeneration. This will lead to the discovery of new pathways and targets involved in enteric neurodegeneration, both in our preclinical models and humans, which will be crucial for the development of novel treatments. Finally, we expect to obtain major novel insights in the cross-talk between enteric neurons and macrophages by studying these two cell populations while they are maturing and interacting in the co-culture system. These experiments will reveal which signaling molecules are used to interact with each other and affect each others function. Taking together, by the end of this project, we expect to have unraveled the role of NA-MF in enteric neurodegeneration and to have identified new targets to improve the clinical management of patients suffering from enteric neuropathies.
In the coming years, we expect to identify the human NA-MF subpopulation in great detail and to uncover their role in enteric neurodegeneration. This will lead to the discovery of new pathways and targets involved in enteric neurodegeneration, both in our preclinical models and humans, which will be crucial for the development of novel treatments. Finally, we expect to obtain major novel insights in the cross-talk between enteric neurons and macrophages by studying these two cell populations while they are maturing and interacting in the co-culture system. These experiments will reveal which signaling molecules are used to interact with each other and affect each others function. Taking together, by the end of this project, we expect to have unraveled the role of NA-MF in enteric neurodegeneration and to have identified new targets to improve the clinical management of patients suffering from enteric neuropathies.