CDNF and MANF Structure and Signalling

Saarma MANF structure

Figure: Solution structure of human MANF protein. PDB ID: 2KVD [6].

Cerebral dopamine neurotrophic factor (CDNF) and mesencephalic astrocyte derived neurotrophic factor (MANF) form an evolutionary conserved protein family with cytoprotective activities in neurons and other cell types [1]. CDNF was originally identified and characterized by our group [2, 3] and is homologous to mammalian MANF protein [4]. A single homologous gene for mammalian MANF/CDNF is also found in invertebrate animals, such as D. melanogaster [5] and C. elegans, in which no other neurotrophic factors have been identified so far.

The molecular mechanism of action and cellular binding partners of CDNF and MANF proteins are still largely unknown. We have resolved the three-dimensional structure of MANF/CDNF proteins by X-ray crystallography and nuclear magnetic resonance (NMR) spectroscopy [6, 7]. The unique 3D structure of MANF/CDNF proteins consists of two domains, an amino-terminal saposin-like domain and a carboxy-terminal SAP-domain that are connected by a flexible linker. We are using the 3D structure model to try to predict and understand how CDNF/MANF proteins interact with other proteins. We have identified regions in the amino-acid sequence of MANF, which are important for its neuroprotective activity [8]. 

MANF and CDNF are localized within the cell in the endoplasmic reticulum (ER) which is an important site of protein synthesis, folding, modification, and transport. Different cellular insults, including exposure to chemicals and viral infections, can disturb the normal ER function leading to the accumulation of misfolded proteins, a condition referred as ER stress. Importantly, ER stress and unfolded protein response (UPR) signaling is activated in pancreatic islets of MANF knockout mice, which develop diabetes [9]. MANF is able to promote cell survival during ER stress but the mechanism behind this is unclear [1]. We are studying the neuroprotective and cytoprotective properties of MANF/CDNF at the molecular level by characterizing their protein-protein interactions. To do this, we use biochemical, molecular, and cell biology methods. We are particularly interested in MANF/CDNF interactions taking place in the ER, and possible roles for MANF and CDNF in the regulation of the UPR signaling pathway.

Our work is also focused on characterizing the levels of endogenous MANF and CDNF proteins in human neurodegenerative and other diseases by using in-lab developed immunoassays [10]. Abnormal CDNF/MANF expression levels may reveal pathological conditions in humans.

References:

  1. Lindahl, M., M. Saarma, and P. Lindholm, Unconventional neurotrophic factors CDNF and MANF: Structure, physiological functions and therapeutic potential. Neurobiol Dis, 2017. 97(Pt B): p. 90-102. 10.1016/j.nbd.2016.07.009
  2. Lindholm, P., et al., Novel neurotrophic factor CDNF protects and rescues midbrain dopamine neurons in vivo. Nature, 2007. 448(7149): p. 73-7. 10.1038/nature05957
  3. Saarma M., Laurén .J., Lindholm P., Timmusk T., and Tuominen R.K. Neurotrophic factor protein and uses thereof. Patent US 7,452,969.
  4. Petrova, P., et al., MANF: a new mesencephalic, astrocyte-derived neurotrophic factor with selectivity for dopaminergic neurons. J Mol Neurosci, 2003. 20(2): p. 173-88.
  5. Palgi, M., et al., Evidence that DmMANF is an invertebrate neurotrophic factor supporting dopaminergic neurons. Proc Natl Acad Sci U S A, 2009. 106(7): p. 2429-34. 10.1073/pnas.0810996106
  6. Hellman, M., et al., Mesencephalic astrocyte-derived neurotrophic factor (MANF) has a unique mechanism to rescue apoptotic neurons. J Biol Chem, 2011. 286(4): p. 2675-80. 10.1074/jbc.M110.146738
  7. Parkash, V., et al., The structure of the conserved neurotrophic factors MANF and CDNF explains why they are bifunctional. Protein Eng Des Sel, 2009. 22(4): p. 233-41. 10.1093/protein/gzn080
  8. Mätlik, K., et al., Role of two sequence motifs of mesencephalic astrocyte-derived neurotrophic factor in its survival-promoting activity. Cell Death Dis, 2015. 6: p. e2032. 10.1038/cddis.2015.371
  9. Lindahl, M., et al., MANF is indispensable for the proliferation and survival of pancreatic beta cells. Cell Rep, 2014. 7(2): p. 366-75. 10.1016/j.celrep.2014.03.023
  10. Galli, E., et al. Increased circulating concentrations of mesencephalic astrocyte-derived neurotrophic factor in children with type 1 diabetes. Sci Rep, 2016. 6:29058. 10.1038/srep29058