Moorthy, Arun

Amyloid fibrils are fibrous protein aggregates that arise from misfolding and self-assembly processes, collectively referred to as amyloidosis. These aggregates are strongly associated with incurable neurodegenerative disorders, including Alzheimer's disease (AD), Parkinson's disease, and Amyotrophic Lateral Sclerosis (ALS). Elevated levels of Reactive Oxygen Species (ROS) and dysregulated metal-ion homeostasis often impaired by environmental and lifestyle factors can induce oxidative stress that undermines cellular antioxidant defenses, which cause the amyloid formation and toxicity. This thesis investigates multiple amyloidosis models, emphasizing the contribution of metal ions and ROS to aggregation pathways, and evaluates the potential inhibitory or protective roles of cytokinin (CK) plant hormone.Chapter 2 focuses on Gelsolin amyloidosis, a hereditary condition driven by point mutations that promote aberrant amyloid formation. Using microscopic and spectroscopic approaches, this work characterizes the aggregation behavior of peptides derived from domain 2 of plasma gelsolin and secreted by muscle cells. Three peptides were studied: the wild-type(WT) sequence and two clinically relevant mutants, K184N and N187Y. Each variant exhibited distinct aggregation rates, reflecting mutation-dependent effects on self-assembly. Furthermore, two CKs Kinetin (Kin) and trans-Zeatin (tZ) were shown to modulate gelsolin aggregation, suggesting their potential as anti-aggregation molecules. Chapter 3 revolves on the aggregation properties of TDP-43 peptides associated with ALS pathology. Within the RRM I domain, two cysteine residues serve as key redox-active sites susceptible to oxidation. ESI-MS and spectroscopic methods were used to analyze three peptide variants: WT, a mutant (MT) in which cysteine were substituted with alanine, and WT-S, a disulfide-linked dimer. All variants displayed higher aggregation under mildly acidic conditions. CKs, Kin and isopentenyl-adenine (iP) showed antioxidant capacity and their influence on peptide stability. Chapter 4 investigates the effects of copper(II)-induced oxidative stress in C2C12 muscle cells and evaluates cellular responses to various CK forms. ESI-MS profiling identified 20 CKs in copper-treated samples and revealed 24 untargeted metabolites with significant level changes, indicating their possible involvement in metal-induced oxidative pathways. In conclusion, this thesis highlights the multifaceted roles of CKs in biological systems, particularly their potential to mitigate ROS overproduction, counteract metal-driven amyloidgenesis, promote fibril destabilization, and lessen oxidative stress.

Author Keywords: Amyloid, Anti aggregation, cytokinins, inhibition, Peptide aggregation, Protein aggregation

Climate-driven permafrost thaw releases microorganisms and dissolved organic matter (DOM) into northern lakes, where their interactions with microbial communities and seasonal processes shape greenhouse gas emissions. In a factorial experiment mixing DOM and microbes from thermokarst ponds and lakes, we found that both DOM and microbial identity strongly influenced degradation. Lake microbes preferentially consumed thermokarst DOM, producing 3× more CO₂ due to low growth efficiency, while thermokarst microbes altered DOM with little CO₂ release. A survey of 40 lakes across a climate gradient showed CO₂ fluxes peaking in spring from under-ice buildup and CH₄ fluxes peaking in fall after summer accumulation. Dissolved gas concentrations served as early indicators of these events, with CH₄ linked to reduced DOM and CO₂ to multiple pathways. Overall, DOM quality, microbial traits, and seasonal dynamics interact to control lake carbon cycling, emphasizing the need for year-round monitoring under climate change.

Author Keywords: Dissolved Organic Matter (DOM), Fluxes, Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR MS), Greenhouse Gases (GHGs), Lakes, Thermokarst