MALDI-MS imaging in glomerular kidney diseases: from diagnostics to precision medicine?

Introduction/Rationale: Glomerular kidney diseases represent the third leading cause of end-stage renal disease in Western countries and the need for both diagnostic and predictive markers is becoming ever more pressing. In particular, there still remains a fair degree of heterogeneity in terms of patient response and outcome and such markers could lead to more targeted therapy and focused monitoring guidelines for clinicians. Given the high degree of tissue heterogeneity associated with these diseases, MALDI-MSI therefore represents an ideal tool in this branch of renal histopathology, offering a complementary molecular dimension. Here we present our recent contributions to this area of research and highlight how this approach can be employed to detect groups of patients which may require more precise therapeutic treatment. Methods: MALDI-MSI was applied to FFPE tissue samples from patients with membranous nephropathy (MN, n=13), diabetic nephropathy (DN, n=9) and hypertensive nephrosclerosis (HN, n=9). For the cases of MN, images were acquired with an ultrafleXtreme™ MALDI-TOF/TOF MS using a single spot laser setting of 40 µm and and raster sampling of 50 μm. For the cases of DN and HN, images were acquired using a rapifleX MALDI Tissuetyper™, employing a single spot laser setting of 18 µm and raster sampling of 20 μm. Finally, in order perform high spatial resolution MALDI-MS imaging, additional cases of MN (n=10) were acquired using a rapifleX MALDI Tissuetyper™, employing a single spot laser setting of 10 µm and a raster sampling of 10 μm. Results: In this preliminary work, we highlight the potential role of MALDI-MS imaging in the precision medicine of two frequently occurring glomerular kidney diseases, membranous nephropathy and diabetic nephropathy. In MN we were able to distinguish groups of patients who responded differentially to standard immunosuppressive therapy and, in particular, observed an increased expression of macrophage migration inhibitory factor (MIF) in patients who did not respond to the treatment. This increased expression of MIF was then validated using immunohistochemistry, with the protein depositing on podocyte and parietal epithelial cells within the glomeruli. When focusing on DN and HN, alterations in the tissue proteome of the two disease groups could clearly be detected. These proteomic alterations were particularly notable at the latter disease stages, even if no discernible differences were evident using routine histology. In particular, four putatively identified proteins were observed to have a higher signal intensity within regions of DN tissue with extensive sclerosis or fibrosis. Among these, two of them (progesterone receptor membrane component 1 and complement component 3) had a signal intensity that increased at the latter stages of the disease and may be associated with progression. Finally, we underline how high spatial resolution MALDI-MSI could further assist in the study of these complex renal diseases by going beyond what was previously possible and visualising the spatial localisation of proteins within the sub-compartments of glomeruli and tubulointerstitium. Conclusions/Novelty: This body of work exemplifies the potential role of MALDI-MSI in renal pathology. Our final goal is to obtain complementary proteomic information that can be used to assist nephrologists in the clinical management of these patients, leading to more targeted therapy and more focused monitoring guidelines. Funding: The research leading to these results has received funding from MIUR: FIRB 2007 (RBRN07BMCT_11), FAR 2014–2016 and in part by Fondazione Gigi & Pupa Ferrari Onlus.