Neurobiology of vital systems

Project 1:  NEK8: A new player in the gene-network linking cilia function to cell cycle regulation

Supervisors: Prof Jacqueline Phillips, Prof Mark Baker

Introduction

Polycystic kidney disease is one of the most common monogenetic disorders affecting approximately 1 in 400 people. Nephronophthisis (NPHP) is a recessive form of polycystic kidney disease that ultimately progresses to kidney failure. NPHP is characterised by diffuse interstitial fibrosis, cortimedullary cysts, and altered tubular basement membrane. Our laboratory has recently identified a single nucleotide polymorphism in NEK8 as the causative mutation responsible for a rodent model of NPHP, the Lewis polycystic kidney disease (LPK) rat (1). NPHP proteins are expressed in the base of the primary cilium and are critical for cell division and ciliary function.

The function of the NEK8 kinase in cilia is unclear and this project aims to identify differences in its activity in mutant cell lines and animal tissues

Hypothesis:

  1. That mutations in different regions of the RCC1 domain of the Nek8 protein causes similar alterations in the expression and co-localisation of Nek8, establishing the importance of the RCC1 domain as a whole rather than the significance of individual regions of the RCC1 structure.
  2. That mutations in the Nek8 protein will significantly alter the kidney epithelial cell proteome, altering key protein network interactions

 

Aims and Research Plan

  1. 1 Establishment and validation of stably transfected cell lines that express wild type human and mutant versions of Nek8, thereby replacing the use of animals to access kidney tissue samples for protein studies.
  2. Compare the impact of mutations in different regions of the RCC1 domain of the Nek8 protein on the level and location of Nek8 expression in the renal epithelial cell line
  3. Determination of the effect of Nek8 mutations on the expression and co-localisation of other proteins known to interact with Nek8 within the cilia, in parallel with analysis of these proteins in human normal and PKD kidney tissues biopsy samples.
  4. Proteomic analysis to assess the impact of the Nek8 mutations on the kidney epithelial cell proteome and in tissues from normal and mutant animals, the study of which will reveal novel and key protein network interactions

Key References:

  1. Phillips, J.K., et al., Temporal relationship between renal cyst development, hypertension and cardiac hypertrophy in a new rat model of autosomal recessive polycystic kidney disease. Kidney and Blood Pressure Research, 2007. 30(3): p. 129-44.
  2. McCooke, J.K., et al., A novel mutation causing nephronophthisis in the Lewis polycystic kidney rat localises to a conserved RCC1 domain in Nek8. BMC Genomics, 2012. 13(393): p. 1471-2164.

Enquires:
Professor Jacqueline Phillips

Email: jacqueline.phillips@mq.edu.au

Project 2:  At the heart of the problem: increased sympathetic drive to the heart in chronic kidney disease patients

Supervisors: Prof Jacqueline Phillips, Assoc Prof Ann Goodchild, Dr Cara Hildreth

Introduction

Chronic kidney disease affects at least 1.7 million Australians, with a further 1 in 3 at risk. For chronic kidney disease patients, the majority of deaths are not related to their diseased kidneys, but rather because their hearts no longer cope. Heart failure, myocardial infarction, abnormal heart rhythms, sudden cardiac death are common consequences of chronic kidney disease. With respect to sudden cardiac death alone this accounts for up to 25% of all deaths in patients that require dialysis and statistically, the chances that a kidney disease patient can be resuscitated and survive following a cardiac arrest are abysmally low, with only 40% surviving the first 48 hours. The one thing that contributes to all these heart-related causes of death is increased sympathetic nerve activity. Yet, because we do not understand why this is elevated in kidney disease patients and how this is impacting on the ability of the heart to function, there is little we can do to treat or prevent this from occurring. Until we do, kidney disease patients will continue to die because of their hearts and not because of their kidneys. This project aimsto to identify what needs to be fixed and how to equip the heart to cope with the challenges of increased sympathetic nerve activity. Only then can we hope to reduce the lethal cardiovascular burden associated with kidney disease.

Hypothesis:

That the sympathetic nervous system excessively drives heart activity in chronic kidney disease, leading to increased risk of sudden cardiac death

Aims:

The overall aim of this research is to identify what occurs in chronic kidney disease to cause the sympathetic nervous system to exert too much command over the heart, with the ultimate goal of identifying mechanisms that we can target to prevent this from occurring. To address this we must identify (1) where the source of the increased sympathetic nervous system control originates and (2) how the heart is responding to this.

Part (1) - where does the increased sympathetic nervous control originate from?

There is a circular relationship between the heart and the sympathetic nervous system, such that nerves project from the heart toward the brain (afferent signals) that influences the activity within the brain (central component) that then changes the nerve output from the brain back to the heart (efferent component).. We will investigate the following aims:

  • Aim 1a: Does increased sympathetic nervous control of the heart result from a change in afferent signalling?
  • Aim 1b: Does increased sympathetic nervous control of the heart result from a change within the central component?
  • Aim 1c: Does increased sympathetic nervous control of the heart result from a change within the efferent component?

Part (2) - how does the heart respond to the sympathetic nervous system?

The sympathetic nervous system is frequently referred to as the 'fight or flight' component of the nervous system and with respect to the heart is responsible for increasing how fast and hard it beats. This is fine when we need to suddenly increase the amount of blood being pumped by the heart, but is not something we want to happen constantly as it leads to a heart muscle hypertrophy and increased work for outcome (effectively thickened, stiff and inefficient heart muscle). Consequently, the heart is designed with protective mechanisms to ensure that this does not happen and does this by ensuring that the parasympathetic nervous system, the 'calm and soothing' component of the nervous system, which slows the heart down and ensures it pumps with graceful efficiency, dominates. This occurs through cross-talk between the two nerves as they enter the heart and how the heart integrates the information it receives. What becomes apparent is that in disease these protective mechanisms are lost. We will identify why in the following aims:

  • Aim 2a: Sympathetic parasympathetic cross-talk - is the sympathetic nervous system turning off the parasympathetic nervous system?
  • Aim 2b: Has the heart lost the ability to properly integrate information from the sympathetic and parasympathetic nervous systems?

Methods:

Using an animal model we will test the reflexes that control the heart rate and determine which parts of the brain are (i) involved in the reflex and (ii) if the functional control is altered.

We will also examine heart tissue taken from both an animal model and human tissue from kidney disease patients and examine the receptors and transporters that control nervous communication in the heart, looking at both the sympathetic and parasympathetic nervous systems, and how they communicate at the level of the heart.

This will allow us to identify the cause of increased sympathetic nerve activity to the heart and the impact that the increased sympathetic nerve activity is having on the heart.

Enquires:
Professor Jacqueline Phillips

Email: jacqueline.phillips@mq.edu.au

Project 3: How can a stressed brain lead to cardiovascular disease?

Supervisors: Prof Jacqueline Phillips, Assoc Prof Ann Goodchild, Dr Cara Hildreth

Introduction

The baroreceptor reflex is essential for survival. In its absence, blood pressure fluctuates too much, placing individuals at an increased risk of death, independent of whether or not the patient has high blood pressure. Baroreflex function is impaired in many diseases, e.g. hypertension, heart failure, Parkinson's disease, Alzheimer's disease, depression and, integral to this proposal, chronic kidney disease (CKD). Despite this high incidence within the general population, little is done to directly treat baroreflex dysfunction, placing these patients at unnecessary risk.

CKD affects at least 1.7 million Australians, with a further 1 in 3 at risk. For CKD patients alone, baroreflex dysfunction is associated with progression to renal failure, a greater chance of cardiovascular events, including sudden cardiac death, which accounts for up to a quarter of all deaths. Baroreflex dysfunction is therefore not a trivial disease feature. But the reality is we are not able to treat baroreflex dysfunction as we still do not understand what causes it. In this project we will identify what mechanisms are accounting for impaired baroreflex function in CKD patients and if these mechanisms may be extrapolated to the wider community by studying this in a model of acquired mitochondrial dysfunction that does not have chronic kidney disease. If we identify a common mechanism for baroreflex dysfunction, this opens the door for research aimed at treating baroreflex dysfunction across a wide spectrum of disorders, in much the same fashion that we treat high blood pressure, pain or infection regardless of the primary disease. The benefits of this will be immeasurable.

Hypothesis:

We hypothesise that this results from damaged/dysfunctional mitochondria placing the brain in a stress-like state (oxidative stress) and altering how it responds to the hormone angiotensin II. We will test this in a model of chronic kidney disease with inherent mitochondrial damage and a model of acquired mitochondrial damage and address the following:

  1. What is the temporal relationship between mitochondrial damage, oxidative stress and changes to angiotensin II responsiveness in relationship to the onset of baroreflex dysfunction.
  2. Does preventing or reversing mitochondrial damage can stop baroreflex damage from occurring and does this occurs by: (a) Improving how the brain responds to baroreflex inputs and/or (b) Correcting brain activity in regions that can govern processing of the baroreflex?

Aims and Research Plan

To achieve this we will use two rodent models - the Lewis Polycystic Kidney (LPK) rat, a model of chronic kidney disease, and Lewis rats treated with L-buthionine sulfoximine (BSO), which causes mitochondrial damage.

Aim 1. What is the temporal relationship between mitochondrial damage, oxidative stress and changes to angiotensin II responsiveness in relationship to the onset of baroreflex dysfunction.

We will examine how well the baroreflex is functioning in the two animal models using a technique called telemetry. This allows us to measure blood pressure and heart rate in conscious animals. From this, we can use computer algorithms to examine how well the baroreflex is working. This will give us a time span over which baroreflex dysfunction occurs in the two models. In both models we will take 3 time points: early, mid and late relative to the development of baroreflex dysfunction. At each of these time points we will measure the following: the degree of mitochondrial damage, the level of oxidative stress and the amount of angiotensin receptor present, and the functional responses of these receptors. We will focus on two brain regions- the nucleus tractus solitarius (NTS) and theparaventricular nucleus of the hypothalamus (PVN), as these are the site of baroreflex input to the brain and a region that governs baroreflex processing, respectively. 

Aim 2. If preventing or reversing mitochondrial damage can stop baroreflex damage from occurring and if this occurs by:

a. Improving how the brain responds to baroreflex inputs.

We will chronically treat both the LPK and BSO treated Lewis with a compound, mitoQ, to improve mitochondrial health in the brain specifically. Under anaesthesia, we will then microinject drugs into the NTS to see if we can alter the ability of the baroreceptor reflex to communicate information. We will block both inhibitory and excitatory neurotransmitter pathways.

b. Correcting brain activity in regions that can govern processing of the baroreflex.

Using the same treatment groups as in Part a, we will perform microinjections in anaesthetised animals that inhibit the PVN. We are seeking to identify if this brain region is over active and as a consequence suppressing the baroreflex, and if this can be restored with mitoQ treatment. We will verify this by performing a separate series of studies where we will block the actions of the hormone vasopressin in the NTS. 

Enquires:
Professor Jacqueline Phillips
Email:
jacqueline.phillips@mq.edu.au

Project 4: How does the brain control blood pressure?

Supervisor: Dr Simon McMullan 

Introduction

Circuits of interconnected 'sympathetic premotor' neurons in the brainstem and midbrain co-ordinate the distribution of blood to different body compartments. The activity of these circuits is vital for life; they maintain brain oxygenation while allowing optimal supply of blood within the body according to competing metabolic, behavioural and environmental demands. For example, their activity allows the body to shunt blood to the gut after meals (to allow digestion), to muscle during physical activity, or away from the skin in response to cold (to retain heat) without any net change in blood pressure, preserving optimal brain perfusion.
However, dysfunction of the sympathetic nervous system is implicated in a variety of cardiovascular diseases and is now accepted as a major pathophysiological driving force in common diseases: increased sympathetic nerve activity is detectable before the onset of hypertension, is the driving force for cardiovascular risk associated with obstructive sleep apnoea, and a key complication associated with heart failure.

No one part of the brain is responsible for controlling blood pressure; instead, sympathetic nerve activity is the sum of activity from multiple parts of the brain. Although the clinical significance of sympathetic nerve overactivity is widely accepted, unravelling the mechanisms that control sympathetic nerve activity, even in healthy individuals, has proved difficult: key hubs of sympathetic premotor neurons have been identified, but the circuit architecture and cellular dynamics that control the activity of these outputs, or interaction between the different hubs, are still poorly understood.

Research Focus:
Our major research focus is to understand the organisation of these circuits. Using a combination of viral tracing (recombinant herpes, monosynaptic restricted rabies) and advanced imaging techniques (CLARITY, confocal) we are currently mapping out the structure of circuits that control blood pressure to generate evidence-based hypotheses, which we will then test using a combination of electrophysiology and optogenetics.
The laboratory is currently interested in recruiting prospective Masters and PhD students interested in helping us to resolve these questions. We are particularly interested in students with neuroanatomical skills (immunohistochemistry, viral tracing, fluorescence or confocal imaging, brain reconstruction using Neurolucida or Imaris software), surgical or neurophysiological experience (nerve recording, microinjection, single cell recording in vitro or in vivo using electrophysiology or optical imaging), although none are prerequisite and we can provide relevant training.

Research Projects:
Research projects can be tailored to the interest and expertise of prospective students, provided they align with the overall goals of the laboratory. However, some examples of projects likely to run in the near future are provided below.

  1. PVN Connectome Project
    One of our research streams is to use genetically restricted rabies vectors to map sources of monosynaptic drive received by sympathetic premotor neurons. This work is already underway and working well; we would like to extend it to include neurons in the paraventricular nucleus of the hypothalamus.
  2. Glia as oxygen sensors
    We hypothesise that astrocytes in the rostral ventrolateral medulla are sensitive to extracellular oxygen concentration and play a role in mediating responses to central hypoxia and ischaemia (the Cushing Reflex). This project will use a combination of viral vectors and optical imaging techniques to determine the oxygen-sensing ability of astrocytes in this region and the role played in mediating hypoxic sympathoexcitation in vivo.
  3. Synchronization of sympathetic and respiratory outputs by sensory stimuli
    We have recently demonstrated that acoustic and visual stimuli can drive potent recruitment of respiratory and sympathetic outputs, and that these effects are gated by structures in the midbrain colliculus. In this project we will use a combination of optogenetic and electrophysiological techniques to examine the pathways responsible for this effect.


Enquires:
Dr Simon McMullan

Email: simon.mcmullan@mq.edu.au