CDNF and MANF Structure and Signaling

Saarma MANF structure

Figure: Solution structure of human MANF protein. PDB ID: 2KVD [7].

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.

In cells, MANF and CDNF localize to the endoplasmic reticulum (ER) which is an important site for protein synthesis, folding, modification, and transport. Different cellular insults, including exposure to toxins or lack of oxygen, 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 [6].

We are studying the molecular mechanism of action and cellular binding partners of CDNF and MANF proteins in order to understand their neuroprotective and cytoprotective functions in more detail. 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 roles of MANF and CDNF in the regulation of UPR signaling pathway.

We have resolved the three-dimensional structure of MANF/CDNF proteins by X-ray crystallography and nuclear magnetic resonance (NMR) spectroscopy [7, 8]. The unique 3D structure of MANF/CDNF proteins consists of two domains, an amino-terminal saposin-like domain and a carboxy-terminal SAP-domain. 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 [9].  We recently demonstrated that MANF directly interacts with an UPR sensor protein IRE1 and regulates its activity thus promoting ER homeostasis and cell survival [10]. We also showed that the survival promoting activity of MANF in primary neurons is dependent on UPR pathways. Using a proteomic approach, we have identified several MANF interacting proteins [11]. We have also characterized the levels of endogenous MANF and CDNF proteins in human neurodegenerative and other diseases using in-lab developed immunoassays [12]. Abnormal CDNF/MANF expression levels could 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. 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
  7. 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
  8. 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
  9. 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
  10. Kovaleva, V., et al., MANF regulates unfolded protein response and neuronal survival through its ER-located receptor IRE1α. 2020: p. 2020.09.22.307744. 10.1101/2020.09.22.307744
  11. Eesmaa, A., et al., The cytoprotective protein MANF promotes neuronal survival independently from its role as a GRP78 cofactor. J Biol Chem, 2021: p. 100295. 10.1016/j.jbc.2021.100295
  12. Galli, E., et al., Increased Serum Levels of Mesencephalic Astrocyte-Derived Neurotrophic Factor in Subjects With Parkinson's Disease. Front Neurosci, 2019. 13: p. 929. 10.3389/fnins.2019.00929