Redundancy in the central tachykinin systems safeguards puberty onset and fertility

Abstract

The tachykinin neurokinin B (NKB, Tac2) is critical for GnRH release. NKB signaling deficiency leads to infertility in humans. However, some patients reverse this hypogonadism resembling the fertile phenotype of Tac2KO and Tacr3KO (encoding NKB receptor, NK3R) mice despite the absence of NKB signaling. Here, we demonstrate that in the absence of NKB signaling, other tachykinins (substance P and neurokinin A [NKA], encoded by Tac1) may take over to preserve fertility. The complete absence of tachykinins in Tac1/Tac2KO mice leads to delayed puberty onset in both sexes and infertility in 80% of females (but not males), in contrast to the 100% fertile phenotype of Tac1KO and Tac2KO mice separately. Furthermore, we demonstrate that NKA controls puberty onset and LH release through NKB-independent mechanisms in the presence of sex steroids and NKB-dependent mechanisms in their absence. In summary, tachykinins interact in a coordinated manner to ensure reproductive success in female mice. 54( Figure 1 D). Of note, first estrous is a more accurate marker of puberty onset as it indicates 55 central activation of the gonadotropic axis. Furthermore, in a fertility test in which adult females 56 were mated with proven fertile WT males, only 20% of Tac1/Tac2 KO females were able to deliver 57 pups over a 90-day long period of mating (Figure 1 E). Moreover, the parturition latency of these 58 small portion of Tac1/Tac2 KO females was longer than in WT controls (WT: 21.66 ± 0.66 days; 59Tac1/Tac2 KO: 29.5 ± 0.5 days; **p<0.01 ) (Figure 1 F) and the litter size was significantly smaller 60 than in controls (WT: 7.33 ± 1.08 pups; Tac1/Tac2 KO: 4 ± 0 pups; **p<0.01) (Figure 1 G). This 61 largely infertile phenotype of Tac1/Tac2 KO females is also supported by the reduced number of 62 corpora lutea in their ovaries (WT: 3.5 ± 0.28 CL/ovary; Tac1/Tac2 KO: 0.75 ± 0.25 CL/ovary; 63 ***p<0.001) (Figure 1 H, I) and significantly lower ovarian weight than controls (WT: 18.50 ± 1.70 64 mg; Tac1/Tac2 KO: 10.83 ± 1.63 mg; **p<0.01). Moreover, since previous studies had 65 documented an improvement of estrous cyclicity with age in Tac2KO mice (8), we assessed 66 whether this was also the case in Tac1/Tac2 KO females at a young (3 months) and older (8 67 months) age and observed that, in both cases, KO females failed to show any signs of regular68 estrous cyclicity (Figure 1 J,K). 69 70 2. Tac1/Tac2 KO females display disrupted LH pulses and response to ovariectomy. 71To further characterize the reproductive phenotype of Tac1/Tac2 KO females, LH pulsatility and 72 long-term response to OVX were assessed. As expected, OVX Tac1/Tac2 KO females displayed 73 a severely disrupted LH pulse pattern (fewer pulses) over 150 minutes compared to OVX WT 74 (WT: 3.33 ± 0.56 pulses/150min; Tac1/Tac2 KO: 1.86 ± 0.26 pulses/150min; *p<0.05) (Figure 2 75 A-C). Interestingly, when the response of LH to OVX was assessed, we observed a biphasic 76 response in which LH levels were reduced compared to WT in Tac1/Tac2 KO and Tac2KO 77 females 2 days post OVX; howev...