MANF and Diabetes
Diabetes mellitus is a group of metabolic disorders characterized by hyperglycaemia. Type 1 diabetes results from the autoimmune destruction of insulin-producing β-cells, leading to total insulin deficiency, whereas type 2 diabetes develops when the β-cells are no longer able to respond to an increased insulin demand due to insulin resistance. The reasons for β-cell destruction in diabetes are still unclear, but increasing evidence implicates endoplasmic reticulum (ER) stress followed by prolonged activation the unfolded protein response (UPR) as a key mechanism. One of the main strategies for improving diabetes therapies is to define and validate novel approaches to protect β-cells from stress, as well as activate their regeneration.
Mesencephalic astrocyte-derived neurotrophic factor (MANF) is a secreted protein that can rescue brain neurons and heart muscle cells from cell death in animal models for Parkinson´s disease, but also in brain and heart ischemia . It is upregulated in cells that actively secrete proteins, and in various situations where protein aggregates accumulate in the endoplasmic reticulum (ER), causing ER stress. The exact mechanism of MANF action is still unknown.
We developed MANF knockout mice, which lack the gene that encodes the MANF protein in all cells. These mice develop severe insulin-deficient diabetes due to progressive postnatal reduction of the β-cell mass, caused by decreased β-cell proliferation and increased β-cell death . Importantly, MANF is needed for the survival of adult mouse β-cells, as induced removal of MANF from this cell population in mice leads to β-cell loss and diabetes (Danilova et al., manuscript). ER stress and sustained activation of the UPR was found to be one of the mechanisms underpinning the destruction of MANF-deficient β-cells in this model. In a separate mouse model of type 1 diabetes, we found that over-expression of MANF in the pancreas enhances β-cell proliferation and prevents β-cell death. Furthermore, recombinant MANF protein stimulates mouse islet β-cell proliferation and protection in culture. Thus, our results demonstrate that MANF constitutes a novel promising therapeutic candidate for β-cell protection and regeneration in diabetes.
When we examined newly diagnosed type 1 diabetic patients, MANF levels were increased in sera  suggesting that MANF can potentially serve as a diagnostic biomarker for young children diagnosed for type 1 diabetes.
Given these clear advances in understanding the role that MANF plays in b-cells and diabetes, our group is continuing to pursue studies into the mechanisms of MANF action in β-cells, as well as other metabolic tissues using transgenic, knockout, and diabetic mouse models.
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- Lindahl, M., Danilova, T., Palm, E., Lindholm, P., Võikar, V., Hakonen, E., Ustinov, J., Andressoo, J.-O., Harvey, B. K., Otonkoski, T., Rossi, J. and Saarma, M. MANF is indispensable for the proliferation and survival of pancreatic b-cells. Cell Rep, 7 (2), 366-75 (2014). 10.1016/j.celrep.2014.03.023
- Galli, E., Härkönen, T., Sainio, M.T., Ustav, M., Toots, U., Urtti, A., Yliperttula, M., Lindahl, M., Knip, M., Saarma, M., Lindholm, P. Increased circulating concentrations of mesencephalic astrocyte-derived neurotrophic factor in children with type 1 diabetes. Sci Rep, June 30, 6: 29058 (2016). 10.1038/srep29058