Ha, Q. | bioRxiv Science

bioRxiv2025

High-Fat Diet-Induced Obesity Impairs Endothelium-Dependent Relaxation via MLCK Activation: Reversal by ML-7 in Rabbits

ObjectiveObesity is an independent risk factor for CVD(cardiovascular diseases) and elevated cardiovascular mortality, though the precise mechanisms remain incompletely elucidated. Impaired endothelium-dependent relaxation is an early manifestation of cardiovascular diseases. This study investigated the impact of HFD(high-fat diet)-induced obesity on endothelium-dependent relaxation function and explored the potential role of MLCK(myosin light chain kinase) signaling. MethodsForty-five New Zealand White rabbits were randomized into three groups: a control group (normal diet), HFD(high-fat diet) group, and an ML-7 group (HFD plus the MLCK inhibitor ML-7). After 8 weeks of feeding, vascular endothelial function was assessed in vivo by measuring FMD(flow-mediated dilation). Serum lipids and blood glucose levels were determined. Endothelium-dependent vasodilation was evaluated ex vivo using aortic ring assays. The protein expression levels of MLCK and eNOS(endothelial nitric oxide synthase), as well as the phosphorylation level of MLC(myosin light chain), in rabbit arteries were analyzed by Western blot. ResultsHFD-fed rabbits developed obesity, dyslipidemia (elevated TC[total cholesterol], LDL-C[low-density lipoprotein cholesterol], and ox-LDL[oxidized low-density lipoprotein]), perirenal adipose tissue deposition, and significant endothelial dysfunction, evidenced by impaired endothelium-dependent relaxation function and morphological endothelial damage. Western blot analysis revealed upregulated MLCK and eNOS expression, along with increased phosphorylation of MLC in the arterial walls of obese rabbits, despite no significant change in NO(nitric oxide) levels compared to controls. Treatment with ML-7 ameliorated endothelium-dependent relaxation function impairment. Furthermore, the inherent limitations of FMD as a non-invasive technique in terms of accuracy and sensitivity for evaluating endothelium-dependent dilation. ConclusionsObesity-induced endothelial dysfunction arise from visceral fat accumulation, dyslipidemia, oxidative stress, and MLCK overexpression. Notably, MLCK inhibition via ML-7 restores vascular function, highlighting its therapeutic potential in obesity-related vascular injury.

physiology↗

bioRxiv2023

Role of Dopamine Neurons in Familiarity

Dopamine neurons signal the salience of environmental stimuli, influencing learning and motivation. However, research has not yet identified whether dopamine neurons also modulate the salience of memory content. Dopamine neuron activity in the ventral tegmental area (VTA) increases in response to novel objects and diminishes as objects become familiar through repeated presentations. We proposed that the declined rate of dopamine neuron activity during familiarization affects the salience of a familiar objects memory. This, in turn, influences the degree to which an animal distinguishes between familiar and novel objects in a subsequent novel object recognition (NOR) test. As such, a single familiarization session may not sufficiently reduce dopamine activity, allowing the memory of a familiar object to maintain its salience and potentially attenuating NOR. In contrast, multiple familiarization sessions could lead to more pronounced dopamine activity suppression, strengthening NOR. Our data in mice reveals that, compared to a single session, multiple sessions result in decreased VTA dopamine neuron activation, as indicated by c-Fos measurements, and enhanced novelty discrimination. Critically, when VTA dopamine neurons are chemogenetically inhibited during a single familiarization session, NOR improves, mirroring the effects of multiple familiarization sessions. In summary, our findings highlight the pivotal function of dopamine neurons in familiarity and suggest a role in modulating the salience of memory content.

animal behavior and cognition↗