Neoexpression of the c-met/Hepatocyte Growth Factor-Scatter Factor Receptor Gene in Activated Monocytes

Distinct genetic risk based on association of MET in families with co-occurring autism and gastrointestinal conditions

OBJECTIVE

In addition to the core behavioral symptoms of autism spectrum disorder, many patients present with complex medical conditions including gastrointestinal dysfunction. A functional variant in the promoter of the gene encoding the MET receptor tyrosine kinase is associated with autism spectrum disorder, and MET protein expression is decreased in the temporal cortex of subjects with autism spectrum disorder. MET is a pleiotropic receptor that functions in both brain development and gastrointestinal repair. On the basis of these functions, we hypothesized that association of the autism spectrum disorder-associated MET promoter variant may be enriched in a subset of individuals with co-occurring autism spectrum disorder and gastrointestinal conditions.

PATIENTS AND METHODS

Subjects were 918 individuals from 214 Autism Genetics Resource Exchange families with a complete medical history including gastrointestinal condition report. Genotypes at the autism spectrum disorder-associated MET promoter variant rs1858830 were determined. Family-based association test and chi(2) analyses were used to determine the association of MET rs1858830 alleles with autism spectrum disorder and the presence of gastrointestinal conditions.

RESULTS

In the entire 214-family sample, the MET rs1858830 C allele was associated with both autism spectrum disorder and gastrointestinal conditions. Stratification by the presence of gastrointestinal conditions revealed that the MET C allele was associated with both autism spectrum disorder and gastrointestinal conditions in 118 families containing at least 1 child with co-occurring autism spectrum disorder and gastrointestinal conditions. In contrast, there was no association of the MET polymorphism with autism spectrum disorder in the 96 families lacking a child with co-occurring autism spectrum disorder and gastrointestinal conditions. chi(2) analyses of MET rs1858830 genotypes indicated over-representation of the C allele in individuals with co-occurring autism spectrum disorder and gastrointestinal conditions compared with non-autism spectrum disorder siblings, parents, and unrelated controls.

CONCLUSION

These results suggest that disrupted MET signaling may contribute to increased risk for autism spectrum disorder that includes familial gastrointestinal dysfunction.

Hepatocyte growth factor–stimulated invasiveness of monocytes

Hepatocyte growth factor (HGF) is a pluripotent cytokine with mitogenic, motogenic, and morphogenic activity for mainly epithelial and endothelial target cells. We previously demonstrated that the specific HGF receptor, MET, is induced in stimulated peripheral blood monocytes. In this study, we analyzed the functional consequences of MET activation in primary cultures of peripheral blood monocytes from healthy donors. After stimulation of MET-expressing monocytes with recombinant HGF, the gene-expression profile of peripheral blood mononuclear cells and monocytes was significantly modulated, especially with regard to genes involved in cell movement. After stimulation of primary cultured monocytes with HGF, invasion assays showed a significantly increased matrigel invasion rate that was completely abolished by neutralizing antibodies to HGF. The HGF-activated invasiveness and the altered gene-expression profile suggest a proinflammatory role for HGF stimulation of monocytes and support the hypothesis that the HGF/MET signaling system plays an important part in the activation of the nonspecific cellular inflammatory response.