Multifaceted roles of prokineticins and prokineticin receptors

More than two decades of research on the prokineticin system show that prokineticins (PKs) are involved in several physiological processes such as angiogenesis, neurogenesis, nociception, regulation of the circadian cycle, and reproduction by acting as angiogenic, anorectic and proinflammatory cytokines, hormones, and neuropeptides. Therefore, mutations, dysfunctions or dysregulations of PKs and their cognate receptors (PKRs) may be involved in various pathologies and trigger disease progression or promote their cure, depending on the pathological insults. After reviewing the current knowledge on the functions of the PK system in health and disease and evidencing the promising effects of PKR non-peptide ligands in various preclinical models, in the present thesis I have highlighted the multifaceted roles of PK2 and PKRs in diseases with a strong neuroinflammatory component such as Parkinson’s disease (PD) and post-COVID-19 olfactory dysfunction (OD) as well as in cancer suggesting the potential of PK2 and PKRs as biomarkers and/or novel therapeutic targets in humans. We investigated the dynamics of PK2 pathway, at both the mRNA and protein levels, in olfactory neurons of PD patients at different disease stages and determined the relationship between PK2 upregulation and clinicopathological features of PD. In particular, the increase in PK2 levels in early disease stages and in accordance with the severity of motor symptoms and the accumulation of α-synuclein suggests that PK2 is neuroprotective in PD where it may serve as both disease biomarker and novel therapeutic target. In addition, we also examined the expression profile of Substance P (SP), a neurotransmitter whose role in PD and olfaction has been extensively described by previous studies. We found a correlation between olfactory neuronal SP and gastrointestinal dysfunction in PD, confirming the reliability of olfactory neurons as a model to study PD progression. Since both PK system and SP have been described as factors involved in olfaction pathophysiology, we evaluated their alterations in olfactory neurons of patients with post-COVID-19 OD compared to healthy controls. We found a significant upregulation of PK2 and, due to the role of PK2/PKR2 in driving the formation of olfactory bulb, we hypothesised that PK2 supports the recovery of the sense of smell following post-COVID-19 OD. In contrast, persistent activation of SP appears to maintain inflammation and contribute to olfactory impairment, counteracting the functions of PK2. These data highlight for the first time the promising role of PKR agonists as a disease-modifying therapy in both PD and post-COVID-19 OD. Finally, we have developed an heterocellular spheroid model of human breast cancer that resemble in vivo tumour organisation to investigate the response of the cancer to doxorubicin (Dox) treatment and to explore the mechanisms involved in both the development of chemoresistance and the efficacy of the drug. We were able to show that hypoxia plays a central role in Dox resistance, while the increase in reactive oxygen species (ROS) is responsible for the achievement of Dox therapeutic effects. Furthermore, we found a direct correlation between ROS and PK2 levels, suggesting the upregulation of PK2 as a potential biomarker for Dox efficacy (pharmacodynamic biomarker). However, despite these promising results that I have reported here, more detailed characterisation of the dynamics of the PK2 pathway in humans is required to validate its clinical value.