Doctoral Dissertations

Date of Award

8-2024

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Chemistry

Major Professor

Thanh D. Do

Committee Members

Michael D. Karlstad, Fred A. Heberle, Bhavya Sharma

Abstract

This dissertation presents an innovative approach utilizing liquid chromatography (LC) coupled with ion mobility spectrometry-mass spectrometry (LC-IMS-MS) to distinguish between mouse insulin 1 (Ins1) and insulin 2 (Ins2). Mice and rats, pivotal in diabetes research, possess two genes encoding these insulin variants, differing primarily in their B-chain sequences at residues 9 and 29. Comprehensive analyses integrating single-islet measurements and investigations into both endogenous and synthetic B-chain peptides elucidate structural disparities between Ins1 and Ins2. These disparities underlie their divergent functions and varying diabetes-related risks.

Through various studies, we elucidate how structural differences affect the functions of Ins1 and Ins2. We uncover the molecular mechanisms linking the inverse relationship between type 2 diabetes (T2D) and migraines by studying the migraine-associated peptide calcitonin gene-related peptide (CGRP). Our data show that CGRP and amylin monomers reduce the secretion of both Ins1 and Ins2, whereas CGRP oligomers have the opposite effect on Ins1. These findings suggest that CGRP regulates insulin secretion and reduces T2D risk, providing a rationale for migraines potentially protecting against T2D.

Furthermore, we show that corticosterone-induced β-cell proliferation may induce insulin resistance. Our findings reveal a significant increase in amylin levels, correlating with an expanded β-cell population. While corticosterone-treated mice exhibit increased β-cell proliferation, the hormones are rapidly degraded. This degradation may compromise insulin efficacy, explaining the observed insulin resistance induced by corticosterone.

This study also delves into the amyloidogenic sequences within the insulin B-chains, particularly the B9-23 sequences. Investigating these sequences reveals differential aggregation propensities, shedding light on the complex interplay between sequence variations and amyloid formation, crucial in diabetes mellitus and related pathologies.

Lastly, by probing pleurin peptides and their nonenzymatic posttranslational modifications (PTMs), including cis/trans proline isomerization, this research aims to elucidate why Ins1 and Ins2 exhibit distinct structures and functions. Cis/trans proline isomerization emerges as a potential determinant of these structural and functional disparities.

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