5-HTR3 and 5-HTR4 located on the mitochondrial membrane and functionally regulated mitochondrial functions

Abstract

5-HT has been reported to possess significant effects on cardiac activities, but activation of 5-HTR on the cell membrane failed to illustrate the controversial cardiac reaction. Because 5-HT constantly comes across the cell membrane via 5-HT transporter (5-HTT) into the cytoplasm, whether 5-HTR is functional present on the cellular organelles is unknown. Here we show 5-HTR3 and 5-HTR4 were located in cardiac mitochondria, and regulated mitochondrial activities and cellular functions. Knock down 5-HTR3 and 5-HTR4 in neonatal cardiomyocytes resulted in significant increase of cell damage in response to hypoxia, and also led to alternation in heart beating. Activation of 5-HTR4 attenuated mitochondrial Ca2+ uptake under the both normoxic and hypoxic conditions, whereas 5-HTR3 augmented Ca2+ uptake only under hypoxia. 5-HTR3 and 5-HTR4 exerted the opposite effects on the mitochondrial respiration: 5-HTR3 increased RCR (respiration control ratio), but 5-HTR4 reduced RCR. Moreover, activation of 5-HTR3 and 5-HTR4 both significantly inhibited the opening of mPTP. Our results provided the first evidence that 5-HTR as a GPCR and an ion channel, functionally expressed in mitochondria and participated in the mitochondria function and regulation to maintain homeostasis of mitochondrial [Ca2+], ROS, and ATP generation efficiency in cardiomyocytes in response to stress and O2 tension.

Intracellular GPCRs Play Key Roles in Synaptic Plasticity

“…Specifically, activation of P2Y1 stimulates mitochondrial Ca 2+ uptake whereas activation of P2Y2 inhibits this process in hepatocytes (49). In cardiomyocytes, activation of 5HT 4 receptors also decreases mitochondrial Ca 2+ uptake and in turn, respiratory chain activity and ATP production (50). Melatonin, as a small, lipophilic ligand, is found in high levels in mitochondria where it can activate MT 1 receptors.…”

An improved method for isolation of mitochondria from cell lines that enables reconstitution of calcium-dependent processes

“…Recently, it has been reported that soluble adenylyl cyclase protein kinase A (sAC-PKA) signaling inside mitochondria regulates ATP production and it also regulates mitochondrial Ca 2+ uptake [5, 6]. More recently, several G-protein coupled receptors that can use calcium as second messengers, such as cannabinoid receptors CB-1 [7], melatonin MT1 receptors [8], GABA B receptors [9], and 5-HT receptors 5- HTR4 [10] have been identified in the mitochondrial membranes. Therefore, in order to understand GPCR function in mitochondria and Ca 2+ -mediated cross-talk between GPCR activity and sAC-PKA signaling, it is essential to investigate optimal mitochondrial Ca 2+ concentrations.…”

Mitochondrial Hormone Receptors - an Emerging Field of Signaling in the Cell’s Powerhouse

“…Nevertheless, even these larger integral membrane proteins can be translocated to mitochondria. One example concerns the serotonin receptor 5-HT 4 [27], which differs from the afore-mentioned ionotropic 5-HT 3 . In functional terms, the mitochondrial 5-HT 4 receptor was reported to decrease the respiration control ratio, contrary to 5-HT 3 , whereas the opening of the permeability transition pore was, again, found to be inhibited [27].…”

“…One example concerns the serotonin receptor 5-HT 4 [27], which differs from the afore-mentioned ionotropic 5-HT 3 . In functional terms, the mitochondrial 5-HT 4 receptor was reported to decrease the respiration control ratio, contrary to 5-HT 3 , whereas the opening of the permeability transition pore was, again, found to be inhibited [27]. Particular insights were obtained by studies on the type-1 cannabinoid receptor CB 1 , which is also translocated to mitochondria [28][29][30][31].…”

“…The nicotinic receptors were reported to be associated with the outer mitochondrial membrane and to be involved in the regulation of apoptosis, partially in a protective way. The 5-HT 3 receptor represents another pentameric, ionotropic receptor type that was found in cardiac mitochondria [27]. However, the receptor was not analyzed with regard to the various 5-HT 3 subtypes, which differ in their composition of subunits.…”