Objective
This proposal aims to investigate changes in islet hormone processing enzyme expression and function over the course of T1D pathogenesis. We will use pancreas tissue from organ donors with T1D, at risk of developing T1D, and those without Diabetes. Gene expression of hormone processing enzymes and markers of beta cell stress will be assessed at the tissue level, and islet prohormones secreted from pancreas tissue slices will be measured across all groups.
Background Rationale
During T1D, insulin-secreting beta cells in the pancreas are attacked by the immune system, leading to insufficient insulin production and high blood glucose levels and T1D diagnosis in these patients. Although the main cell type affected in T1D is the pancreatic beta cell, other cell types are also affected. For example, plasma glucagon levels (the major glucose-increasing hormone secreted by pancreatic alpha cells) are high in patients with T1D, further contributing to symptoms of T1D. Moreover, it has been established that the production of these hormones is impaired in T1D, as precursors of these (prohormones) can be detected in the serum of patients with T1D and used as biomarkers to predict disease development. However, whether hormone processing defects are a cause or consequence of T1D is not clear.
Description of Project
During type 1 diabetes (T1D) development, pancreatic islets are infiltrated by a variety of cells representing the immune system, the downstream impact being a loss of insulin-secreting beta cells. Indeed, this loss results in hyperglycemia, which eventually forms the basis for a diagnosis of overt disease. While it is clear that the primary cell type targeted in T1D is the pancreatic beta cell, increasing evidence suggests that additional cell types are also affected by this disorder. For example, plasma glucagon levels, the major counterregulatory hormone secreted by pancreatic alpha cells, are increased in patients with T1D, a factor that likely contributes to the challenge of hyperglycemia. Additionally, precursors of islet cell hormones are often detected at unusual levels in the serum of individuals with T1D, suggesting that the production and processing of these hormones is altered in the disorder’s pathogenesis. Indeed, expression levels of the enzymes responsible for hormone processing (i.e., prohormone convertases) are decreased in the T1D pancreas. Whether this is a cause or consequence of T1D is not fully understood. This proposal seeks to investigate changes in the expression of these hormone-processing enzymes at the cellular level across the natural history of T1D. To achieve this, I will utilize pancreas tissue obtained from organ donors with T1D, those at risk for developing the disease, and those without diabetes; all obtained from the nPOD biobank. Specifically, gene expression will be assessed using innovative spatial transcriptomics technology. Beyond this, prohormone secretion will be measured utilizing stored samples (>30 cases) from glucose-stimulated pancreas tissue slices and markers of cellular stress will be assessed in the perifused slices to investigate associations between cellular stress and defective hormone processing in T1D. I hypothesize that expression levels of hormone-processing enzymes will decrease in the early phases of T1D development, together with observing increased release of partially processed islet hormones relative to mature hormones (e.g., insulin, glucagon). Prospective slice culture experiments will further allow for a means to define specific mechanistic pathways that meet the challenges associated with beta cell protein processing in T1D. These efforts, if successful, may not only lead to an improved understanding of mechanisms vital to the pathogenesis of T1D but in addition, the development of novel biomarkers and avenues for therapeutic intervention
Anticipated Outcome
I anticipate that tissue from donors at risk of developing T1D will show decreased levels of prohormone processing enzymes and increased markers of cellular stress, which will correlate with a relative increase in the levels of partially processed hormones in slice secretion samples. Using slice cultures, compounds that improve islet cell hormone processing and function will be identified and hopefully used to inform the development of new treatments for T1D.
Relevance to T1D
The vast majority of T1D treatment, seeking prevention of disease or preservation of insulin production in those recently diagnosed with the disorder, focus on immune cells. My proposed efforts will diverge from the norm through the investigation of additional mechanisms using rare and highly unique tissues and remarkably novel techniques. If and when successful, these experiments should help the community by discerning the mechanisms of hormone processing defects and potentially inform new treatments to restore islet cell function.