Background
(1)GnRH
Gonadotropin-releasing hormone (GnRH), formerly referred to as the luteinizing hormone-releasing hormone (LHRH), is produced and secreted primarily by the hypothalamus in a pulsatile fashion, and acts on the anterior pituitary gland to release luteinizing hormone (LH) and follicle stimulating hormone (FSH). These two gonadotropins have downstream effects on the peripheral reproductive organs essential for maturation and fertility.
Figure 1: Female & male HPG axis
Isolated gonadotropin-releasing hormone (GnRH) deficiency (IGD) is characterized by inappropriately low serum concentrations of the gonadotropins LH (luteinizing hormone) and FSH (follicle-stimulating hormone) in the presence of low circulating concentrations of sex steroids. IGD is associated with a normal sense of smell (normosmic IGD) in approximately 40% of affected individuals and an impaired sense of smell (Kallmann syndrome) in approximately 60%. IGD can first become apparent in infancy, adolescence, or adulthood. Infant boys with congenital IGD often have micropenis and cryptorchidism. Adolescents and adults with IGD have clinical evidence of hypogonadism and incomplete sexual maturation on physical examination. Adult males with IGD tend to have prepubertal testicular volume (i.e., < 4 mL), absence of secondary sexual features (e.g., facial and axillary hair growth, deepening of the voice), decreased muscle mass, diminished libido, erectile dysfunction, and infertility. Adult females have little or no breast development and primary amenorrhea. Although skeletal maturation is delayed, the rate of linear growth is usually normal except for the absence of a distinct pubertal growth spurt[2].
(2)Pulsatile GnRH administration
Treatment options for patients with secreting GnRH disorder include sex steroids, gonadotropins, and pulsatile GnRH administration[3].While either gonadotropin therapy or pulsatile GnRH stimulation[4] can induce spermatogenesis in approximately 90%-95% of men with IGD, some men have a better response to pulsatile GnRH stimulation than to gonadotropin therapy[5].
Subcutaneous administration of GnRH in a pulsatile manner through a portable pump that delivers a GnRH bolus every two hours is an efficient way of inducing testicular growth and spermatogenesis[4]. As the primary defect of IGD is typically localized to the hypothalamus, the pituitary responds appropriately to physiologic doses of GnRH.
Figure 2: Pulsatile GnRH administration
However, we cannot ignore that pulsatile GnRH stimulation has a few disadvantages, one of the most worrying problems is that this method of frequent injections can easily lead to infection.
(3)Our inspiration
Restoration of full endocrine pancreatic function is met in a relatively small number of patients via transplantation of cadaveric whole pancreas or islets[7]. Thus, our team got the inspiration to associate stem cell transplantation with pulsatile GnRH administration, which means design an engineered cell that can be injected inside human body and release GnRH in a pulsatile fashion. The cell may solve the problems in the current therapies, such as high risk infection.
Figure 3: The engineering cell secreting GnRH in a pulsatile fashion
Our solution
Our team expect to construct a cell which is able to secrete GnRH in a cycle of 2 to 5 hours through genetically engineering and synthetic biology. If the following experiment conducted smoothly, then we may inject it into the human body by subcutaneous entrapment, and corresponding measures are taken to prevent immune rejection.
(By the way, we have not made a plan to conduct animal or human experiments yet.)
Design
(1)Aim
Our team GnRH Timer aims to design an engineering cell which can secrete GnRH in a cycle of 2 to 5 hours, to provide a new idea to treat GnRH secretory disorders.
(2)Key ideas
We have used three key plasmids to achieve pulsatile GnRH expression, they were VP64, KRAB and GnRH.
Figure 4: Schematics of the engineering cell
Briefly speaking, we used the site competition between VP64 and KRAB to achieve pulsatile expression and ensure that its expression is not continuous. At the same time, the same promoter synchronizes the expression of GnRH and KRAB, achieving pulsatile expression of GnRH.
(3)Result
At present, our design has been verified in the laboratory, and we can successfully control the engineering cell to express GnRH in a pulsatile fashion.
References
[1]Wickramasuriya N, Hawkins R, Atwood C, Butler T. The roles of GnRH in the human central nervous system. Horm Behav. 2022 Sep;145:105230. doi: 10.1016/j.yhbeh.2022.105230. Epub 2022 Jul 6. PMID: 35809386; PMCID: PMC9990468.
[2]Emons G, Gründker C. The Role of Gonadotropin-Releasing Hormone (GnRH) in Endometrial Cancer. Cells. 2021 Feb 1;10(2):292. doi: 10.3390/cells10020292. PMID: 33535622; PMCID: PMC7912811.
[3]Balasubramanian R, Crowley WF Jr. Isolated Gonadotropin-Releasing Hormone (GnRH) Deficiency. 2007 May 23 [updated 2022 May 12]. In: Adam MP, Mirzaa GM, Pagon RA, Wallace SE, Bean LJH, Gripp KW, Amemiya A, editors. GeneReviews® [Internet]. Seattle (WA): University of Washington, Seattle; 1993–2023. PMID: 20301509.
[4]Boehm U, Bouloux PM, Dattani MT, de Roux N, Dodé C, Dunkel L, Dwyer AA, Giacobini P, Hardelin JP, Juul A, Maghnie M, Pitteloud N, Prevot V, Raivio T, Tena-Sempere M, Quinton R, Young J. Expert consensus document: European Consensus Statement on congenital hypogonadotropic hypogonadism--pathogenesis, diagnosis and treatment. Nat Rev Endocrinol. 2015;11:547–64.
[5]Pitteloud N, Hayes FJ, Dwyer A, Boepple PA, Lee H, Crowley WF Jr. Predictors of outcome of long-term GnRH therapy in men with idiopathic hypogonadotropic hypogonadism. J Clin Endocrinol Metab. 2002b;87:4128–36.
[6]Balasubramanian R, Crowley WF Jr. Isolated Gonadotropin-Releasing Hormone (GnRH) Deficiency. 2007 May 23 [updated 2022 May 12]. In: Adam MP, Mirzaa GM, Pagon RA, Wallace SE, Bean LJH, Gripp KW, Amemiya A, editors. GeneReviews [Internet]. Seattle (WA): University of Washington, Seattle; 1993–2023. PMID: 20301509.®
[7]Loretelli C, Assi E, Seelam AJ, Ben Nasr M, Fiorina P. Cell therapy for type 1 diabetes. Expert Opin Biol Ther. 2020 Aug;20(8):887-897. doi: 10.1080/14712598.2020.1748596. Epub 2020 Apr 17. PMID: 32299257.
