Heterogeneity of Lipid and Protein Cartilage Profiles Associated with Human Osteoarthritis with or without Type 2 Diabetes Mellitus

Abstract

Osteoarthritis (OA) is a multifactorial pathology and comprises a wide range of distinct phenotypes. In this context, the characterization of the different molecular profiles associated with each phenotype can improve the classification of OA. In particular, OA can coexist with type 2 diabetes mellitus (T2DM). This study investigates lipidomic and proteomic differences between human OA/T2DM^- and OA/T2DM⁺ cartilage through a multimodal mass spectrometry approach. Human cartilage samples were obtained after total knee replacement from OA/T2DM^- and OA/T2DM⁺ patients. Label-free proteomics was employed to study differences in protein abundance and matrix-assisted laser desorption/ionization (MALDI) mass spectrometry imaging (MSI) for spatially resolved-lipid analysis. Label-free proteomic analysis showed differences between OA/T2DM^- and OA/T2DM⁺ phenotypes in several metabolic pathways such as lipid regulation. Interestingly, phospholipase A2 protein was found increased within the OA/T2DM⁺ cohort. In addition, MALDI-MSI experiments revealed that phosphatidylcholine and sphingomyelin species were characteristic of the OA/T2DM^- group, whereas lysolipids were more characteristic of the OA/T2DM⁺ phenotype. The data also pointed out differences in phospholipid content between superficial and deep layers of the cartilage. Our study shows distinctively different lipid and protein profiles between OA/T2DM^- and OA/T2DM⁺ human cartilage, demonstrating the importance of subclassification of the OA disease for better personalized treatments.

Keywords: MALDI-MSI; cartilage; diabetes; label-free proteomics; osteoarthritis; spatially resolved-lipid analysis.

Figure 1

Relative intensities of apolipoprotein A-1 and phospholipase A2 proteins in OA/T2DM^– and OA/T2DM⁺ cohorts. Apolipoprotein A1 protein has been found increased in the OA/T2DM^– group, whereas phospholipase A2 protein has been found increased in the OA/T2DM⁺ group (*adjusted p-value ≤0.05).

Figure 2

Linear discriminant analysis of OA/T2DM^– and OA/T2DM⁺ patients based on their lipid signature. (A) Discriminant function 1 (DF1) score projection. (B) DF1 scaled loading spectrum.

Figure 3

Linear discriminant analysis of superficial and deep cartilage layers based on their specific lipid signature. (A) DF1 score projection. (B) DF1 scaled loading spectrum of the superficial and deep layers of human cartilage. The LDA analysis was performed on both groups.

Figure 4

μMALDI experiment at 15 μm raster size. (A) Segmentation of OA/T2DM^– tissue (top) and OA/T2DM⁺ tissue (bottom). The transitional layers are represented by yellow and pink colors, the lacunae in light blue color and the chondrocyte cells in blue color. (B) pLSA analysis with random initialization. The superficial layer (blue) is represented by component 1 and the deep layer (purple) is represented by component 4. (C) Safranin O staining. (D) pLSA loading spectra of selected components 1 and 4.