Investigating the regulation of kisspeptin neurons in functional hypothalamic amenorrhoea (FHA)

Problem:

Menstrual disturbance affects one-fifth of women of reproductive age. Functional hypothalamic amenorrhoea (FHA) is one of the commonest causes responsible in one-third of cases. FHA occurs due to a combination of low body-weight, excessive exercise, and stress, on a background of genetic susceptibility.

FHA causes subfertility and adverse effects on bone and cardiovascular health. At present, the mechanisms underlying FHA are incompletely understood, and treatment options are limited e.g., gonadotrophin releasing hormone (GnRH) pump therapy is the first-line treatment, but is scarcely available. Other available treatments including clomiphene are less effective in FHA.

Therefore, there is an unmet research need to advance our understanding of the pathways underlying FHA and to develop novel therapeutic approaches to improve care for affected women. Context:

Kisspeptin is the key regulator of GnRH neurons and the reproductive endocrine axis. Evidence suggests that kisspeptin is the 'GnRH pulse generator'. Leptin is a major signal of energy availability and is reduced in FHA.

Leptin is a permissive signal that is requisite for healthy GnRH neuronal function, and leptin treatment can restore GnRH pulses in women with FHA although with undesirable associated weight-loss. However, existing data suggest that leptin does not act directly on kisspeptin neurons, but rather via an intermediary neuron such as agouti-related peptide (AgRP) neurons in the hypothalamus. AgRP neurons abundantly express leptin receptors and physically connect to kisspeptin neurons.

Hypothesis:

I hypothesise that leptin inhibits AgRP neurons, which in turn regulate kisspeptin neurons to play a causal role in the pathophysiology of FHA. Aims: 1. Validate a novel mouse model of FHA.

My pilot data shows increased AgRP expression in two independent mouse models of FHA. Whilst 'caloric-restriction' is an established model of FHA, our lab has recently developed a novel 'caloric-dilution' model of FHA. This model uses a low-calorie feed such that mice can eat without restriction until they feel satiated such that hunger pathways should not be activated.

However, they do not eat sufficiently to avoid a calorie deficit, and thus could be a more representative model of women with FHA. I will characterise the reproductive phenotype in this new model of FHA and compare it to the established model. 2. Investigate the causative role of hyperactive AgRP neurons in driving the FHA phenotype.

As the models of FHA have increased AgRP activity (see pilot data), I will use inhibitory Designer Receptors Exclusively Activated by Designer Drugs (DREADD)-based technology to reduce AgRP-neuronal activity to evaluate the impact on reproductive hormone levels and phenotype (e.g. uterine / ovarian weight).

3. Determine whether chronic kisspeptin administration can restore a healthy reproductive phenotype in the mouse models of FHA.

I will administer a subcutaneous infusion of kisspeptin via a micro-osmotic pump for 2 weeks to the two mouse models of FHA and assess whether reproductive health can be restored. 4. Determine whether chronic kisspeptin administration can restore ovulation in women with FHA.

I will conduct a clinical study in women with FHA to assess whether a chronic infusion of kisspeptin for 2 weeks can restore ovulation. Applications and benefits:

This research will significantly advance our understanding of the mechanisms underlying FHA and establish whether AgRP neurons regulate kisspeptin neurons to result in FHA. I will evaluate the therapeutic potential of kisspeptin administration both in mouse models of FHA and in women with FHA.