Dysfunction of the ANS has severe impacts on multiple organs and systems. The mechanisms of the dysfunction remain unknown. Thus, we utilized drastic and innovative interventions to the ANS, such as the application of endotoxin, optogenetics, and transgenic mice, and made several new findings.
One of the life-threatening dysfunction of the ANS is the irreversible hypotension and vascular hyporeactivity in septic shock. To understand mechanisms, we reproduced
hyporeactivity of the mesenteric arteries with the treatment of endotoxin LPS overnight in vitro
and screened out a few vasoactive agents that have vasoconstriction effects. Three candidates, ET-1, 5-HT, and vasopressin, are found effective, which have never been used for clinical management for septic shock. Besides, U46619, an agonist of the TXA2 receptor, can partially reverse the hyporeactivity. In the system, these vasopressors may play a role not only as an individual but also as a combination with other vasoconstrictors. Indeed, we have found that the vasoconstriction effects of these agents are significantly potentiated by co-application with PE. Our results suggest that the endotoxin-induced vascular hyporeactivity is not attributed to the damage of VSM in the early phase (first 24 hours) of septic shock, neither to the over-
released vasodilators from endothelium. The main reason for the septic hypotension seems to be caused by vascular hyporeactivity to α adrenoceptors that are unfortunately the main targets in the current therapeutic management of septic shock. Although the underlying mechanism for the vascular hyporeactivity is still elusive, our dissections of intracellular signaling pathways
revealed that ET-1 acts on ETAR and works through Gi – AC – PKA and Gq/11 – PC – PLC – DAG – PKC signaling pathway, while 5-HT activates ROK through 5-HT1BR leading to
inhibition of the myosin light-chain phosphatase (MLCP) and vasoconstriction. Since some of these signaling pathways are shared by the α adrenoceptor system, it is likely that the
dysfunction of the α adrenoceptor system may occur in upstream pathways. Taken together, this pharmaceutical research may provide new and effective therapeutical intervention of septic shock.
The endothelium regulates vascular homeostasis by releasing a variety of vasoactive substances including vasoconstrictors and vasodilators, while how the endothelial activation affects vascular tones is unknown. Current belief is vasodilation, as the overall function of the endothelium in vasomotor is vasodilation through the NO-dependent signaling pathway. This inner layer system we worked on is located inside of blood vessels. Therefore, it was a challenge to choose an effective intervention method to activate ECs selectively without affecting the VMS. To address this, we generated transgenic mice with ChR expression in the ECs throughout the whole body persistently in a life-long time scale. Optostimulation on dissected EC evoked depolarization and vasoconstriction in perfused heart and kidney. This is the first direct evidence demonstrating that activation of EC leads to vasoconstriction. Also, our results indicated that such opto-vasoconstriction is fast, reproducible, long-lasting that is comparable in strength to the popular vasoconstrictor PE. Meanwhile, we performed another study applying optogenetics in VSMC and demonstrated that optostimulation in VSMC induces significant vasoconstriction that is fast, reproducible, light intensity-dependent, and comparable in strength to popular
vasoconstrictors (Wu et al., 2015).
These studies open a new avenue to applying optogenetics in peripheral system, especially cardiovascular system, by passing potential inference from adjacent tissues, even as close as VSMC and ECs are in blood vessels. With the successful application of optogenetics in
peripheral system, we were confident to dig further with effective intervention in the CNS. We chose the breathing control as it is the most important function of the ANS within the brain. Dysfunction of breathing in certain genetic diseases, such as RTT. NE production and projection play a critical role in the regulation of breathing in the CNS while NE synthesis is deficient in both RTT mouse model and patients. Also, the primary area for NE production is located in LC, where neurons are hyperexcitable. Such neuronal hyperexcitability may be a compensatory response to the inadequate NE, or an adverse manifestation of the disease. To understand whether the increased LC neuronal excitability improves NE modulation, we generated a new strain of double transgenic mice with Mecp2 null and ChR expression in LC neurons. The TH- ChR-Mecp2‒/Y mice exhibit typical phenotypes seen in other mouse models of RTT including hypoactivity, low body weight, short life span, and hind limb clasping. They also show clear breathing disorders, including significant higher apnea counts and more frequent breathing f variation than the TH-ChR control. We found that the NE-ergic modulation of hypoglossal neurons is impaired in the double transgenic mice but not in the control mice. The defected NE projection is not improved with optostimulation, suggesting that LC neuronal hyperexcitability does not seem beneficial to the NE modulation in RTT. Instead, the neuronal hyperexcitability may worsen the homeostatic status of local neuronal networks in the LC.