Search

Introduction: Profilin1 (PFN1) is a ubiquitously expressed protein known for its function as a regulator of actin polymerization and dynamics. A recent discovery linked mutant PFN1 to Amyotrophic Lateral Sclerosis (ALS), which is a fatal and progressive motor neuron disease. We have also demonstrated that Gly118Val mutation in PFN1 is a cause of ALS, and the formation of aggregates containing mutant PFN1 may be a mechanism for motor neuron death. Hence, we were interested in investigating the aggregation of PFN1 further and searching for co-aggregated proteins in our mouse model overexpressing mutant PFN1. Methods: We investigated protein aggregation in several tissues of transgenic and no-transgenic mice using western blotting. To further understand the neurotoxicity of mutant PFN1, we conducted a pull-down assay using an insoluble fraction of spinal cord lysates from hPFN1G118V transgenic mice. For this assay, we expressed His6-tagged PFN1WT and PFN1G118V in E. coli and purified these proteins using the Ni-NTA column. Results: In this study, we demonstrated that mutant PFN1 forms aggregate in the brain and spinal cord of hPFN1G118V mice, while WT-PFN1 remains soluble. Among these tissues, spinal cord lysates were found to have PFN1 bands at higher molecular weights recognized with anti-PFN1. Moreover, the pull-down assay using His6-PFN1G118V showed that Myelin Binding Protein (MBP) was present in the insoluble fraction. Conclusion: Our analysis of PFN1 aggregation in vivo revealed further details of mutant PFN1 aggregation and its possible complex formation with other proteins, providing new insights into the ALS mechanism.

The hydrogen/deuterium exchange (HDX) is a reliable method to survey the dynamic behavior of proteins and epitope mapping. Matrix-Assisted Laser Desorption Ionization-Time of Flight Mass Spectrometry (MALDI-TOF MS) is a quantifying tool to assay for HDX in the protein of interest. We combined HDX-MALDI-TOF MS and molecular docking/MD simulation to identify accessible amino acids and analyze their contribution in the structural changes of profilin1 (PFN1). The molecular docking/MD simulations are computational tools for enabling the analysis of the type of amino acids that may be involved via HDX identified under the lowest binding energy condition. Glycine to Valine amino acid (G117V) substitution mutation is linked to amyotrophic lateral sclerosis (ALS). This mutation is found to be in the actin-binding site of PFN1 and prevents the dimerization/polymerization of actin and invokes a pathologic toxicity that leads to ALS. In this study, we sought to understand the PFN1 protein dynamic behavior using purified wild type and mutant PFN1 proteins. The data obtained from HDX-MALDI-TOF MS for PFN1WT and PFN1G117V at various time intervals, from seconds to hours, revealed multiple peaks corresponding to molecular weights from monomers to multimers. PFN1/Benzaldehyde complexes identified 20 accessible amino acids to HDX that participate in the docking simulation in the surface of WT and mutant PFN1. Consistent results from HDX-MALDI-TOF MS and docking simulation predict candidate amino acid(s) involved in the dimerization/polymerization of PFNG117V. This information may shed critical light on the structural and conformational changes with details of amino acid epitopes for mutant PFN1s’ dimerization, oligomerization, and aggregation.

Glycyrrhiza glabra (G. glabra) has been used as a flavoring and sweetener agent, in addition to its therapeutic properties. It is rich in phytoestrogen and may prevent osteoporosis caused by estrogen deficiency; however, there is no evidence for its effects on proliferation and osteogenesis in mesenchymal stem cells. So, we were encouraged to investigate whether the ethyl acetate extract of licorice root as a source of phytoestrogen can act similar to estrogen in cell culture. Furthermore, the analysis of the licorice extract (LE) based on HPLC-DAD-ESI-MS indicated that LE comprises phytoestrogen compounds, such as glabridin and glabrene. In this study, the effects of LE on proliferation of human bone-marrow mesenchymal stem cells (hBM-MSCs) were investigated using MTT assay. In addition, its effects on the osteogenesis were evaluated using alkaline phosphatase activity (ALP), calcium deposition, and bone specific gene expression such as ALP, osteocalcin, Runx2, and BMP-2. The quantitative gene expression was studied by real-time RT-PCR. Our results showed a significant increase in proliferation in presence of LE in concentration 10-50 µg/mL. The differentiation of hBM-MSCs increased in doses of LE (10-25 µg/mL) compared to the control group. The effects of LE were similar to those of 17β-estradiol (E2) (10-8 M) and were abolished by ICI 182,780 an antagonist of estrogen receptor (ER) (10-7), indicating that the stimulatory effects of LE occur through estrogen receptor-mediated mechanism . Taking these into account, LE may be a potential candidate for prevention of osteoporosis in menopausal women.

Single amino acid mutations in profilin 1 (PFN1) have been found to cause amyotrophic lateral sclerosis (ALS). Recently, we developed a mouse model for ALS using a PFN1 mutation (glycine 118 to valine, G118V), and we are now interested in understanding how PFN1 becomes toxically lethal with only one amino acid substitution. Therefore, we studied mutation-related changes in the PFN1 protein and hypothesized that such changes significantly disturb its structure. Initially, we expressed and studied the purified PFN1(WT) and PFN1(G118V) proteins from bacterial culture. We found that the PFN1(G118V) protein has a different mean residue ellipticity, as measured by far-UV circular dichroism, accompanied by a spectral shift. The intrinsic fluorescence of PFN1(G118V) showed a small fluctuation in maximum fluorescence absorption and intensity. Moreover, we examined the time course of PFN1 aggregation using SDS-PAGE, western blotting, and MALDI-TOF/TOF and found that compared with PFN1(WT), PFN1(G118V) had an increased tendency to form aggregates. Dynamic light scattering data confirmed this, showing a larger size distribution for PFN1(G118V). Our data explain why PFN1(G118V) tends to aggregate, a phenotype that may be the basis for its neurotoxicity.