Functional consequences of AXL sequence variants in hypogonadotropic hypogonadism.
BACKGROUND
Prior studies showed that Axl /Tyro3 null mice have delayed first estrus and abnormal cyclicity due to developmental defects in GnRH neuron migration and survival.


OBJECTIVE
The objective of the study was to test whether the absence of Axl would alter reproductive function in mice and that mutations in AXL are present in patients with Kallmann syndrome (KS) or normosmic idiopathic hypogonadotropic hypogonadism (nIHH).


METHODS
The sexual maturation of Axl null mice was examined. The coding region of AXL was sequenced in 104 unrelated, carefully phenotyped KS or nIHH subjects. Frequency of mutations was compared with other causes of GnRH deficiency. Functional assays were performed on the detected mutations.


RESULTS
Axl null mice demonstrated delay in first estrus and the interval between vaginal opening and first estrus. Three missense AXL mutations (p.L50F, p.S202C, and p.Q361P) and one intronic variant 6 bp upstream from the start of exon 5 (c.586-6 C>T) were identified in two KS and 2 two nIHH subjects. Comparison of the frequencies of AXL mutations with other putative causes of idiopathic hypogonadotropic hypogonadism confirmed they are rare variants. Testing of the c.586-6 C>T mutation revealed no abnormal splicing. Surface plasmon resonance analysis of the p.L50F, p.S202C, and p.Q361P mutations showed no altered Gas6 ligand binding. In contrast, GT1-7 GnRH neuronal cells expressing p.S202C or p.Q361P demonstrated defective ligand dependent receptor processing and importantly aberrant neuronal migration. In addition, the p.Q361P showed defective ligand independent chemotaxis.


CONCLUSIONS
Functional consequences of AXL sequence variants in patients with idiopathic hypogonadotropic hypogonadism support the importance of AXL and the Tyro3, Axl, Mer (TAM) family in reproductive development.
Division of Endocrinology, Metabolism, and Diabetes (S.S.-M., M.X., A.J.K., M.E.W.), Division of Cardiology (D.S., M.T.), and Department of Biochemistry and Molecular Genetics (S.B., R.S.H.), University of Colorado School of Medicine, Aurora, Colorado 80045; Veterans Affairs Research Service (M.E.W.), Veterans Affairs Medical Center, Denver, Colorado 80220; and Harvard Reproductive Endocrine Science Center and the Reproductive Endocrine Unit (L.P., W.F.C.), Department of Medicine, Massachusetts General Hospital, Boston, Massachusetts 02114.
S
S
Salian-Mehta
M
M
Xu
A J
AJ
Knox
L
L
Plummer
D
D
Slavov
M
M
Taylor
S
S
Bevers
R S
RS
Hodges
W F
WF
Crowley
M E
ME
Wierman
D000293:Adolescent; D000328:Adult; D000818:Animals; D002478:Cells, Cultured; D005260:Female; D056726:Genetic Association Studies; D006801:Humans; D007006:Hypogonadism / Q000235:genetics*; D017436:Kallmann Syndrome / Q000235:genetics; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D010375:Pedigree; D020641:Polymorphism, Single Nucleotide; D011518:Proto-Oncogene Proteins / Q000235:genetics*; D020794:Receptor Protein-Tyrosine Kinases / Q000235:genetics*; D012741:Sexual Maturation / Q000235:genetics; D055815:Young Adult; D000094963:Axl Receptor Tyrosine Kinase
D011518:Proto-Oncogene Proteins; D020794:Receptor Protein-Tyrosine Kinases; D000094963:Axl Receptor Tyrosine Kinase