Chemokine CXCL4 interactions with extracellular matrix proteoglycans mediate widespread immune cell recruitment independent of chemokine receptors.

Leukocyte recruitment from the vasculature into tissues is a crucial component of the immune system but is also key to inflammatory disease. Chemokines are central to this process but have yet to be therapeutically targeted during inflammation due to a lack of mechanistic understanding. Specifically, CXCL4 (Platelet Factor 4, PF4) has no established receptor that explains its function. Here, we use biophysical, in vitro, and in vivo techniques to determine the mechanism underlying CXCL4-mediated leukocyte recruitment. We demonstrate that CXCL4 binds to glycosaminoglycan (GAG) sugars on proteoglycans within the endothelial extracellular matrix, resulting in increased adhesion of leukocytes to the vasculature, increased vascular permeability, and non-specific recruitment of a range of leukocytes. Furthermore, GAG sulfation confers selectivity onto chemokine localization. These findings present mechanistic insights into chemokine biology and provide future therapeutic targets.

Monitoring the early aggregatory behaviour and size of Aß1-42 in the absence & presence of metal ions using dynamic light scattering.

BACKGROUND AND AIM: Aß1-42 is an amyloidogenic peptide found within senile plaques extracted from those who died with a diagnosis of Alzheimer's disease. The potent neurotoxicity of this peptide is related to its propensity to form aggregated conformations in vivo, a process that is influenced by the species and concentration of metal ions present within the local environment. This study examines the impact of different metals upon the early aggregatory behaviour and size of Aß1-42 under simulated physiological conditions. METHODS: The size and aggregatory behaviour of Aß1-42 in the presence and absence of metal ions was monitored during the initial 30 min of fibril formation in real-time using dynamic light scattering. RESULTS: Intensity scattering measurements showed a clear tendency towards aggregation with regards to Aß1-42 only solutions (10 µM). Both equimolar Al3+ & Cu2+ lowered and stabilised the dimensions of Aß1-42 aggregates; however, a diminutive but significant increase in size was still observed over a 30-min period. While excess Al3+ continued to supress the size of Aß1-42, a 10-fold increase in the concentration of Cu2+ accelerated peptide aggregation relative to that observed for equimolar metal but not compared to Aß1-42 alone. CONCLUSION: These results infer that Al3+ ions stabilise and aid in the maintenance of smaller, toxic intermediates while excess Cu2+ facilitates the formation of larger, more inert, amorphous species exceeding 1 µm in size. Furthermore, we propose that metal-induced toxicity of Aß1-42 is reflective of their ability to preserve smaller oligomeric species in vitro.