Leptin Excites Proopiomelanocortin Neurons via Activation of TRPC Channels

Abstract

Leptin can exert its potent appetite-suppressing effects via activation of hypothalamic proopiomelanocortin (POMC) neurons. It depolarizes POMC neurons via activation of a yet unidentified nonselective cation current. Therefore, we sought to identify the conductance activated by leptin using whole-cell recording in EGFP-POMC neurons from transgenic mice. The TRPC channel blockers SKF96365 (1-[␤-[3-(4-methoxyphenyl)propoxy]-4-methoxyphenethyl]-1H-imidazole hydrochloride), flufenamic acid, and 2-APB (2-aminoethyl diphenylborinate) potently inhibited the leptin-induced current. Also, lanthanum (La 3ϩ ) and intracellular Ca 2ϩ potentiated the effects of leptin. Moreover, the diacylglycerol-permeable analog OAG (2-acetyl-1-oleoyl-sn-glycerol) failed to activate any TRPC current. Using a Cs ϩ -gluconate-based internal solution, the leptin-activated current reversed near Ϫ20 mV. After replacement of external Na ϩ and K ϩ with Cs ϩ , the reversal shifted to near 0 mV, and the I/V curve exhibited a negative slope conductance at voltages more negative than Ϫ40 mV. Based on scRT-PCR, TRPC1 and TRPC4 -7 mRNA were expressed in POMC neurons, with TRPC5 being the most prevalent. The leptin-induced current was blocked by the Jak2 inhibitor AG490, the PI3 kinase inhibitor wortmannin, and the phospholipase C inhibitors, U73122 and ET-18-OCH3. Notably, we identified PLC␥1 transcripts in the majority of POMC neurons. Therefore, leptin through a Jak2-PI3 kinase-PLC␥ pathway activates TRPC channels, and TRPC1, 4, and 5 appear to be the key channels mediating the depolarizing effects of leptin in POMC neurons.

Prolactin Regulates Tuberoinfundibular Dopamine Neuron Discharge Pattern: Novel Feedback Control Mechanisms in the Lactotrophic Axis

“…The LV component proved sensitive to 2-APB, a blocker of TRPC1, TRPC3, TRPC4, TRPC5, and TRPC6 channels, yet insensitive to SKF96365, a blocker of TRPC6 and TRPC7 channels (Clapham et al, 2005). This pharmacological profile is similar to that reported for the cholecystokinin-activated MCC in rat amygdala interneurons (Chung and Moore, 2009) but distinct from that reported for leptin responses in Arc POMC neurons, effects mediated via the activation of another member of the class I cytokine receptor family, Ob-Rb (Qiu et al, 2010).…”

“…3C), in which an LV and a HV component could be identified. The inward current responsible for depolarization-the LV component-exhibits a negative slope conductance (approximately Ϫ50 mV) and is attenuated in Na ϩ -substituted aCSF and augmented in low-Ca 2ϩ /high-Mg 2ϩ aCSF (Qiu et al, 2010). This suggests a Na ϩ -dominated MCC mediated through TRPC channels.…”

“…As with other members of the class I cytokine receptor superfamily, e.g., Ob-Rb, this involves numerous signal transduction pathways, including Janus kinase (JAK)/ signal transducer and activator of transcription and phosphoinositide 3-kinase (PI3K) Ma et al, 2005a,b). Surprisingly, the JAK inhibitor AG490 (10 M), a compound known to inhibit the rapid TRPC-dependent effects of leptin in Arc pro-opiomelanocortin (POMC) and kisspeptin neurons (Qiu et al, 2010(Qiu et al, , 2011, failed to block the Prlinduced inward current (V Hold ϭ Ϫ60 mV; Ϫ23.5 Ϯ 5.1 pA; n ϭ 4; p Ͼ 0.05 vs control), nor did it significantly alter the HV component of I Prl (V Hold ϭ ϩ40 mV; Ϫ209.8 Ϯ 108.7 pA; n ϭ 3; p Ͼ 0.05 vs control; Fig. 8).…”

“…8). The enzyme PI3K is also known to be essential for both the rapid TRPC-dependent effects of leptin in POMC and kisspeptin neurons (Qiu et al, 2010(Qiu et al, , 2011 and the membrane insertion of TRPC channels (Bezzerides et al, 2004). A 15 min preincubation with the potent and irreversible PI3K inhibitor wortmannin (200 nM), like AG490, failed to inhibit I Prl at V Hold ϭ Ϫ60 mV (Ϫ18.9 Ϯ 3.2 pA; n ϭ 8; p Ͼ 0.05 vs control), it did however abolish the HV component (V Hold ϭ ϩ40 mV; 220.9 Ϯ 119.5 pA; n ϭ 5; p Ͼ 0.005 vs control; Fig.…”

The Roles of Rasd1 small G proteins and leptin in the activation of TRPC4 transient receptor potential channels

“…69 Leptin is also considered a proinflammatory adipokine because of the actions it exerts in several cells of the immune system, including monocytes/macrophages, dendritic cells, neutrophils, eosinophils, basophils, natural killer cells, and lymphocytes. [70][71][72][73] Qiu et al 74 suggested that a Janus 2 tyrosine kinase (Jak 2)-dependent pathway via stimulation of PI3 kinase and PLCgamma1 activated TRPC channels. Therefore, we think that leptin through a Jak2-PI3 kinase-PLCgamma pathway may activate TRPC4b channels in INS-1 cells.…”