LRRK2 expression in normal and pathologic human gut and in rodent enteric neural cell lines

Biphenotypic Cells and α-Synuclein Accumulation in Enteric Neurons of Leucine-Rich Repeat Kinase 2 Knockout Mice

BACKGROUND

Leucine-rich repeat kinase 2 is a molecule that is responsible for familial Parkinson's disease. Our previous findings revealed that leucine-rich repeat kinase 2 is expressed in the enteric nervous system. However, which cells in the enteric nervous system express leucine-rich repeat kinase 2 and whether leucine-rich repeat kinase 2 is associated with the structure of the enteric nervous system remain unclear. The enteric nervous system is remarkable because some patients with Parkinson's disease experience gastrointestinal symptoms before developing motor symptoms.

AIMS

We established a leucine-rich repeat kinase 2 reporter mouse model and performed immunostaining in leucine-rich repeat kinase 2 knockout mice.

METHODS

Longitudinal muscle containing the myenteric plexus prepared from leucine-rich repeat kinase 2 reporter mice was analyzed by immunostaining using anti-green fluorescent protein (GFP) antibody. Immunostaining using several combinations of antibodies characterizing enteric neurons and glial cells was performed on intestinal preparations from leucine-rich repeat kinase 2 knockout mice.

RESULTS

GFP expression in the reporter mice was predominantly in enteric glial cells rather than in enteric neurons. Immunostaining revealed that differences in the structure and proportion of major immunophenotypic cells were not apparent in the knockout mice. Interestingly, the number of biphenotypic cells expressing the neuronal and glial cell markers increased in the leucine-rich repeat kinase 2 knockout mice. Moreover, there was accumulation of α-synuclein in the knockout mice.

CONCLUSIONS

Our present findings suggest that leucine-rich repeat kinase 2 is a newly recognized molecule that potentially regulates the integrity of enteric nervous system and enteric α-synuclein accumulation.

Emerging perspectives on precision therapy for Parkinson's disease: multidimensional evidence leading to a new breakthrough in personalized medicine

PD is a prevalent and progressive neurodegenerative disorder characterized by both motor and non-motor symptoms. Genes play a significant role in the onset and progression of the disease. While the complexity and pleiotropy of gene expression networks have posed challenges for gene-targeted therapies, numerous pathways of gene variant expression show promise as therapeutic targets in preclinical studies, with some already in clinical trials. With the recognition of the numerous genes and complex pathways that can influence PD, it may be possible to take a novel approach to choose a treatment for the condition. This approach would be based on the symptoms, genomics, and underlying mechanisms of the disease. We discuss the utilization of emerging genetic and pathological knowledge of PD patients to categorize the disease into subgroups. Our long-term objective is to generate new insights for the therapeutic approach to the disease, aiming to delay and treat it more effectively, and ultimately reduce the burden on individuals and society.

The relationship between extreme inter-individual variation in macrophage gene expression and genetic susceptibility to inflammatory bowel disease

The differentiation of resident intestinal macrophages from blood monocytes depends upon signals from the macrophage colony-stimulating factor receptor (CSF1R). Analysis of genome-wide association studies (GWAS) indicates that dysregulation of macrophage differentiation and response to microorganisms contributes to susceptibility to chronic inflammatory bowel disease (IBD). Here, we analyzed transcriptomic variation in monocyte-derived macrophages (MDM) from affected and unaffected sib pairs/trios from 22 IBD families and 6 healthy controls. Transcriptional network analysis of the data revealed no overall or inter-sib distinction between affected and unaffected individuals in basal gene expression or the temporal response to lipopolysaccharide (LPS). However, the basal or LPS-inducible expression of individual genes varied independently by as much as 100-fold between subjects. Extreme independent variation in the expression of pairs of HLA-associated transcripts (HLA-B/C, HLA-A/F and HLA-DRB1/DRB5) in macrophages was associated with HLA genotype. Correlation analysis indicated the downstream impacts of variation in the immediate early response to LPS. For example, variation in early expression of IL1B was significantly associated with local SNV genotype and with subsequent peak expression of target genes including IL23A, CXCL1, CXCL3, CXCL8 and NLRP3. Similarly, variation in early IFNB1 expression was correlated with subsequent expression of IFN target genes. Our results support the view that gene-specific dysregulation in macrophage adaptation to the intestinal milieu is associated with genetic susceptibility to IBD.

From the Gut to the Brain: The Role of Enteric Glial Cells and Their Involvement in the Pathogenesis of Parkinson's Disease

The brain-gut axis has been identified as an important contributor to the physiopathology of Parkinson's disease. In this pathology, inflammation is thought to be driven by the damage caused by aggregation of α-synuclein in the brain. Interestingly, the Braak's theory proposes that α-synuclein misfolding may originate in the gut and spread in a "prion-like" manner through the vagus nerve into the central nervous system. In the enteric nervous system, enteric glial cells are the most abundant cellular component. Several studies have evaluated their role in Parkinson's disease. Using samples obtained from patients, cell cultures, or animal models, the studies with specific antibodies to label enteric glial cells (GFAP, Sox-10, and S100β) seem to indicate that activation and reactive gliosis are associated to the neurodegeneration produced by Parkinson's disease in the enteric nervous system. Of interest, Toll-like receptors, which are expressed on enteric glial cells, participate in the triggering of immune/inflammatory responses, in the maintenance of intestinal barrier integrity and in the configuration of gut microbiota; thus, these receptors might contribute to Parkinson's disease. External factors like stress also seem to be relevant in its pathogenesis. Some authors have studied ways to reverse changes in EGCs with interventions such as administration of Tryptophan-2,3-dioxygenase inhibitors, nutraceuticals, or physical exercise. Some researchers point out that beyond being activated during the disease, enteric glial cells may contribute to the development of synucleinopathies. Thus, it is still necessary to further study these cells and their role in Parkinson's disease.

Potential roles of enteric glial cells in Crohn's disease: A critical review

Enteric glial cells in the enteric nervous system are critical for the regulation of gastrointestinal homeostasis. Increasing evidence suggests two-way communication between enteric glial cells and both enteric neurons and immune cells. These interactions may be important in the pathogenesis of Crohn's disease (CD), a chronic relapsing disease characterized by a dysregulated immune response. Structural abnormalities in glial cells have been identified in CD. Furthermore, classical inflammatory pathways associated with CD (e.g., the nuclear factor kappa-B pathway) function in enteric glial cells. However, the specific mechanisms by which enteric glial cells contribute to CD have not been summarized in detail. In this review, we describe the possible roles of enteric glial cells in the pathogenesis of CD, including the roles of glia-immune interactions, neuronal modulation, neural plasticity, and barrier integrity. Additionally, the implications for the development of therapeutic strategies for CD based on enteric glial cell-mediated pathogenic processes are discussed.

Are LRRK2 mysteries lurking in the gut?

Gut-brain axis and inflammation are two hot topics in Parkinson's disease (PD). In this setting, the leucine-rich repeat kinase 2 (LRRK2) gene, which encodes the eponym protein, has attracted much attention. LRRK2 is not only the gene most commonly associated with Parkinson's disease but also a susceptibility gene for Crohn's disease (CD), thereby suggesting that it may sit at the crossroads of gastrointestinal inflammation, Parkinson's, and Crohn's disease. In contrast to the accumulated data on LRRK2 in the central nervous system (CNS), research on LRRK2 in the digestive tract is still in its infancy, and the scope of the present review article is therefore to review existing studies on LRRK2 in the gastrointestinal tract in both physiological and pathological conditions. In light of current data on LRRK2 in the gastrointestinal tract, we discuss if LRRK2 could be or not regarded as a molecular link between gut inflammation, Parkinson's disease, and Crohn's disease, and we suggest directions for future research.

Immunological Features of LRRK2 Function and Its Role in the Gut-Brain Axis Governing Parkinson's Disease

Emerging evidence implicates intestinal involvement in the onset and/or progression on the selective degeneration of dopaminergic neurons characterizing Parkinson's disease (PD). On the one hand, there are studies supporting the Braak hypothesis that holds that pathologic α-synuclein, a hallmark of PD, is secreted by enteric nerves into intestinal tissue and finds its way to the central nervous system (CNS) via retrograde movement in the vagus nerve. On the other hand, there is data showing that cells bearing leucine-rich repeat kinase 2 (LRRK2), a signaling molecule with genetic variants associated with both PD and with inflammatory bowel disease, can be activated in intestinal tissue and contribute locally to intestinal inflammation, or peripherally to PD pathogenesis via cell trafficking to the CNS. Importantly, these gut-centered factors affecting PD development are not necessarily independent of one another: they may interact and enhance their respective pathologic functions. In this review, we discuss this possibility by analysis of studies conducted in recent years focusing on the ability of LRRK2 to shape immunologic responses and the role of α-synuclein in influencing this ability.