Proteoglycans (PGs) are pivotal components of extracellular matrices, involved in a variety of processes such as migration, invasion, morphogenesis, differentiation, drug resistance, and epithelial-to-mesenchymal transition (EMT). Cellular plasticity is a crucial intermediate phenotypic state acquired by cancer cells, which can modulate EMT and the generation of cancer stem cells (CSCs). PGs affect cell plasticity, stemness, and EMT, altering the cellular shape and functions. PGs control these functions, either by direct activation of signaling cascades, acting as co-receptors, or through regulation of the availability of biological compounds such as growth factors and cytokines. Differential expression of microRNAs is also associated with the expression of PGs and their interplay is implicated in the fine tuning of cancer cell phenotype and potential. This review summarizes the involvement of PGs in the regulation of EMT and stemness of cancer cells and highlights the molecular mechanisms.

Aims: Vascular atherosclerotic calcification is a pathological process marked by the abnormal deposition of calcium minerals in the intima. Asporin (ASPN) is a small leucine-rich proteoglycan which interacts with collagen and calcium. Due to its role in matrix mineralization, we hypothesized that ASPN might act as a regulator of vascular calcification, thereby promoting atherosclerotic plaque stability. Methods and results: ASPN protein, analysed by ELISA, was quantified in 176 carotid endarterectomy plaques (Carotid Plaque Imaging Project cohort, including 98 patients with cerebrovascular symptoms and 78 asymptomatic patients). Plaque composition was assessed by histological, biochemical, and immunological assays, along with bulk RNA sequencing, to investigate the role of ASPN in atherosclerosis. Patients donating plaques were followed up for post-operative cardiovascular events, median follow-up 6.58 years. The effect of ASPN on smooth muscle cell (SMC) differentiation and matrix mineralization was investigated in vitro using human vascular SMCs overexpressing ASPN. Increased ASPN protein levels were observed in plaques from asymptomatic patients compared with patients with cerebrovascular symptoms. ASPN protein levels were positively associated with markers of plaque stability and regulation of extracellular matrix remodelling while showing an inverse relationship with calcification. Patients with high intraplaque ASPN had a lower risk for future cardiovascular events. Mechanistically, ASPN overexpression in vascular SMCs reduced matrix mineralization in vitro, supporting its potential role in plaque stabilization. Conclusion: ASPN is a regulator of vascular calcification in atherosclerosis, promoting a plaque phenotype that is less prone to rupture. Additionally, high ASPN levels are associated with fewer future cardiovascular events.

Inflammation contributes to the destabilization of atherosclerotic plaques and increases the risk of cardiovascular events such as myocardial infarction and stroke. Extracellular matrix components modulate inflammation and immune responses within the plaque microenvironment. Serglycin (SRGN), is a proteoglycan primarily expressed by immune cells that regulates inflammation, but its role in human atherosclerotic plaques remains unclear. SRGN protein levels were quantified by ELISA in carotid endarterectomy samples from patients in the Atherosclerotic Plaque Imaging Project and compared between symptomatic and asymptomatic plaques. SRGN spatial localization was evaluated by multispectral imaging and histology. Glycosylation patterns were examined by immunoprecipitation and immunoblotting. Functional effects were investigated using CRISPR-mediated SRGN knockout in THP-1 monocytes differentiated into macrophages and exposed to oxidized low-density lipoprotein (oxLDL). SRGN levels were higher in plaques from asymptomatic patients compared with plaques from symptomatic patients and localized primarily to macrophage- and lipid-rich regions. Plaque SRGN was positively associated with histological markers of plaque stability, displayed heterogeneous molecular forms and showed an inverse association with the plaque vulnerability index. In vitro, SRGN deficiency was associated with a more pro-inflammatory macrophage profile, impaired M2-like polarization, and increased lipid retention following oxLDL exposure. These findings indicate that SRGN is associated with inflammatory cell presence, lipid accumulation, and features of plaque stability in human plaques, and suggest a role for SRGN in macrophage differentiation and lipid handling in atherosclerotic lesions.