Cardiovascular disease is the leading cause of mortality in the US in which obesity is an independent risk factor. Obesity suppresses parasympathetic nervous system (PSNS) activity. PSNS impairment is independently associated with poor outcomes in heart disease patients; however, current clinical treatments do not directly augment PSNS activity. A critical barrier to therapeutic development is an insufficient understanding of molecular mechanisms involved in PSNS withdrawal.
Peripheral PSNS impairment seen in animal models of cardiovascular disease is suspected to occur at PSNS ganglia and/or nerve terminals due to attenuated synthesis/release of acetylcholine (ACh). Thus, choline transporter (CHT), the rate-limiting molecule in ACh synthesis, is particularly important. Recent studies suggest CHT internalization is regulated by ubiquitination. Thus, the original hypothesis was alternations in ubiquitination/deubiquitination enhanced CHT internalization and degradation, reduced ACh synthesis, and led to PSNS impairment. This was addressed using a cholinergic cell line and high fat diet (HFD) obese mouse model.
In cells, TUBE assay confirmed CHT polyubiquitination, which was increased during proteasome, lysosome, or deubiquitinating enzyme inhibition. Immunoprecipitation demonstrated a physical interaction between CHT and UCHL1 (ubiquitin carboxyl-terminal hydrolase 1), a deubiquitinating enzyme essential for cholinergic signaling. UCHL1 knockdown decreased native CHT; increased CHT polyubiquitination; and altered CHT plasma membrane translocation. These data indicate that UCHL1 regulates CHT protein expression in vitro. This notion was further supported by in vivo data, specifically immunohistochemistry showing UCHL1 and CHT colocalization in atrial ganglia and attenuation of vagus nervus stimulation (VNS)-induced bradycardia following pharmacologic UCHL1 inhibition in mice.
In diet-induced obesity, HFD mice had a blunted response to VNS indicative of PSNS withdrawal. However, no clear association between atrial protein levels of CHT, UCHL1, and PSNS dysfunction were observed. Unexpectedly, while acetylcholinesterase was unchanged, there was a 2-fold increase in butyrylcholinesterase (BChE), which also can hydrolysis ACh. Although minimally affecting baseline heart rate of regular diet mice, selective pharmacologic BChE inhibition augmented VNS-induced bradycardia, partially rescuing PSNS impairment in HFD mice. In summary, these findings suggest the possible mechanistic role of increases in atrial BChE in obesity-induced PSNS suppression and propose a novel mechanism to ameliorate PSNS function by inhibiting BChE activity.
|Commitee:||Martin, Douglas, Rezvani, Khosrow, Schlenker, Evelyn, Talley, Robert, Wang, Hongming|
|School:||University of South Dakota|
|Department:||Basic Biomedical Sciences|
|School Location:||United States -- South Dakota|
|Source:||DAI-B 78/02(E), Dissertation Abstracts International|
|Keywords:||Butyrylcholinesterase (bche), Choline transporter (cht), Obese mice, Parasympathetic nervous system, Sn56 cells, Uchl1|
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