Vijay Sai Josyula: Nerve-macrophage association in the pancreas in health and disease:  Investigating emerging components of pancreatic neuro-immune communication

Abstract

The pancreatic islet provides a site for close communication between sympathetic nerves and macrophages, which together help preserve the immune balance. However, how this neuro-immune dialogue influences the development of type 1 diabetes (T1D) remains unclear. This thesis explores the role of the chemokine receptor CX3CR1 and its ligand CX3CL1(fractalkine) in orchestrating macrophage–nerve interactions within the islet, using a combination of transcriptomic, flow cytometry, live imaging and functional approaches.

In Paper 1, single-cell RNA sequencing (scRNA-seq) of non-obese diabetic (NOD) mice identified a subset of nerve-associated macrophages (NAMs) expressing Cx3cr1, Siglech, and Tmem119, showing transcriptional similarities to microglia. These NAMs progressively declined with Type 1 diabetes(T1D) development, paralleling a loss of sympathetic innervation. Gene ontology analysis suggested that NAMs exert immunoregulatory effects through cytokine and chemokine signaling pathways.

In Paper 2, confocal microscopy and spectral flow cytometry were used to analyse CX3CR1 deficient mice. The absence of CX3CR1 resulted in reduced islet innervation and macrophage density, while the overall macrophage phenotypes remained unchanged. This disrupted nerve–macrophage association correlated with a delayed onset of T1D, highlighting the role of CX3CR1 in maintaining neuro-immune organization within islets.

In Paper 3, live pancreatic slice imaging was used to track macrophage motility and T cell interactions in real time. Neither CX3CR1 deletion nor acute pharmacological inhibition affected short-term macrophage dynamics, suggesting that CX3CR1 predominantly regulates long-term structural organization rather than immediate cellular behaviour.

In Paper 4, a 3D co-culture model was established to visualize live interactions between sympathetic neurons, pancreatic islets, and immune cells within an agarose matrix, providing a flexible platform for studying neuro-immune mechanisms in real time.

Collectively, these studies reveal that CX3CR1 dependent macrophage–nerve communication is essential for maintaining islet innervation and immune homeostasis. Disruption of this signaling axis alters neuro-immune architecture and delays the onset of T1D.