Circulating makorin ring-finger protein-3 (MKRN3) levels in healthy men and in men with hypogonadotropic hypogonadism

Constitutional delay of puberty versus congenital hypogonadotropic hypogonadism: Genetics, management and updates

Delayed puberty (DP) affects approximately 2% of adolescents. In the vast majority of patients in both sexes, it is due to constitutional delay of growth and puberty (CDGP), a self-limited condition in which puberty starts later than usual but progresses normally. However, some CDGP patients may benefit from medical intervention with low-dose sex steroids or peroral aromatase inhibitor letrozole (only for boys). Other causes of DP include permanent hypogonadotropic hypogonadism, functional hypogonadotropic hypogonadism (due to chronic diseases and conditions), and gonadal failure. In this review we discuss these themes along with the latest achievements in the field of puberty research, and include a brief synopsis on the differential diagnosis and management of patients with CDGP and congenital hypogonadotropic hypogonadism.

Mkrn3 functions as a novel ubiquitin E3 ligase to inhibit Nptx1 during puberty initiation

Central precocious puberty (CPP) is attributed to the disorder of some trigger factors those can activate the hypothalamic-pituitary-gonadal axis controlled by GnRH neurons. Many recent studies reveal one of those trigger factors, Makorin ring finger protein 3 (Mkrn3), whose loss-of-function mutations are implicated in CPP. Although Mkrn3 contained zinc Ring finger domain is considered as a putative E3 ubiquitin ligase, its actual function is never reported. Here, our results demonstrated that in mice hypothalamus before and when puberty initiated, Mkrn3 expressed the reversed tendency with Nptx1, which is an important secreted protein for neuron development. Furthermore, our data manifested that Mkrn3 interacted and suppressed Nptx1 activity. And the Ring finger domain of Mkrn3 contained was determined to be essential for binding with Nptx1 for its polyubiquitination during the puberty initiation. Our study shed light on the molecular insights into the function of Mkrn3 in the events of puberty initiation.

Circulating makorin ring finger protein 3 levels decline in boys before the clinical onset of puberty

OBJECTIVE

Makorin ring finger protein 3 (MKRN3) gene restrains the hypothalamic-pituitary-gonadal axis. In girls, peripheral levels of MKRN3 decline prior to the onset of puberty. We described longitudinal changes in serum MKRN3 levels in boys before and during puberty and assessed the effect of inhibition of estrogen biosynthesis on MKRN3 levels.

DESIGN

Longitudinal serum samples from a double-blind, randomized controlled study in 30 boys (age range: 9.1-14.2years) with idiopathic short stature who received placebo (Pl; n=14) or aromatase inhibitor letrozole (Lz; 2.5mg/day; n=16) for 2years.

METHODS

We analyzed the relationships between serum MKRN3 and clinical and biochemical markers of puberty by using summary measures.

RESULTS

Serum MKRN3 declined by 669±713 pg/mL per year (P<0.001). This change was biphasic, as the levels decreased during Tanner genital stage G1 (-2931±2750 pg/mL per year) and plateaued thereafter (-560±1510 pg/mL per year) (P<0.05). During G1, MKRN3 levels in Lz-treated subjects decreased slower than in Pl-treated boys (-782±3190 vs -2030±821 pg/mL per year, P<0.05). The decrease in serum MKRN3 levels in G1 was associated with increases in LH (r=-0.5, P<0.01), testosterone (r=-0.6, P<0.01), and inhibin B (r=-0.44, P<0.05) (n=26).

CONCLUSION

Peripheral MKRN3 levels in boys appear to serve as a readout of the diminishing central inhibition that controls the onset of puberty.