Circadian Biology & Parkinson’s Disease: The Clock is Ticking

Parkinson’s disease involves significant disruption to the circadian clock. A loss of normal clock gene expression leads to a desynchronization of fundamental biological and physiological processes. These findings open the door for circadian rhythm-based treatments for neurological diseases such as Parkinson’s.

Parkinson’s disease is characterized as a loss of dopaminergic neurons within the substantia nigra region of the mid-brain. The accumulation of alpha synuclein-based protein aggregates such as Lewy bodies are concurrent with the progression of the disease. Similar to other neurological diseases such as Alzheimer’s, the standard medical approach offers no solutions, but only palliative-based treatments. Many of the treatments, including the drug L-DOPA act as catalysts to the degenerative process, and over time become part of the pathophysiology. Emerging research provides substantial evidence that Parkinson’s disease not only involves significant disruption to circadian clock gene functions, but that circadian rhythm dysfunction may be a major etiological catalyst to the disease itself.

Parkinson’s disease is the second most common neurodegenerative disease worldwide. Between 7-10 million people worldwide suffer from it. The frequency is higher over age 80, with an estimated 1,900 out of 100,000 people affected. 4% of people with Parkinson’s are diagnosed before the age of 50. Men are 1.5x more likely to develop Parkinson’s than women. In the U.S., roughly one million Americans are diagnosed with the condition, and the annual cost including treatment, disability and related costs is around 25 billion dollars each year (R), (R), (R).

Circadian Biology & Parkinson’s

Among their myriad regulatory functions over the rhythmicity of biological systems, circadian clock genes regulate the sleep cycle. For some time it has been presumed that sleep disturbances are a consequence of neurodegenerative diseases. However, emerging research is showing that circadian and sleep disturbances may actually be driving the pathophysiology of neurodegenerative diseases (R).

REM sleep disorders such as RBD (REM sleep behavior disorder) are strongly predictive of Parkinson’s disease, and are among the most common non-motor-related symptoms of the disease, affecting roughly 50% of patients (R), (R). Idiopathic rapid eye movement sleep behavior disorder (IRBD) is strongly predictive of neurodegenerative disorders, especially over time (R). A 2013 study tracked 29 males over the age of 50 for 16 years. The study demonstrated that 81% of patients diagnosed with IRBD developed Parkinson’s /dementia (R). Subsequent longitudinal research findings have confirmed that IRBD is strongly predictive of developing a synucleinopathy (Parkinson’s, Lewy body dementia, MSA) over time.

Circadian rhythms are driven by a 24-hour internal clock. The SCN of the hypothalamus (suprachiasmatic nuclei) is in effect the primary pacemaker of the circadian system. Biological clock genes located in this region of the brain, contain thousands of nuclei which orchestrate circadian functions. Additionally, most peripheral cells contain these same clock genes, and are cued to express, based upon several variables.

All cellular life is entrained by nature to behave rhythmically, and in synchronization with the 24-hour diurnal clock. In disease states, these rhythms are often desynchronized, leading to abnormal expression of biological and physiological systems. This understanding envisions a progressive model of clinical evaluation and treatment. This model invites metabolic profiling and testing to be viewed within the context of the rhythmic expression of biological systems during a 24-hour cycle. Furthermore, understanding the influence of the circadian rhythm envisions chronobiological therapeutics, the timing of therapies: light and dark exposures, food, fasting, supplements, drugs, exercise, sleep, wake, rest.

6 Primary Variables Affecting the Circadian Clock

Circadian clock gene expression is influenced by cues from the environment. These cues serve as epigenetic signals, in effect guiding the transcription of circadian clock genes. The 6 most fundamental variables governing circadian entrainment in most lifeforms on planet earth are:

• Light and dark
• Caloric availability and caloric deficit
• Hot and Cold: changes to body temperature

The exposure of light from the sun during daytime and darkness at nighttime is the most ancient and fundamental diphasic tandem influencing circadian biology. In addition, caloric availability also influences the expression of circadian clock genes. Fasting and caloric restriction induces the transcription of SIRT-1, the primary histone deacetylase that activates the BMAL1 clock gene, triggering the 24-hour clock. The changing seasons caused by the variation in tilt of the earth’s axis in its orbit around the sun leads to seasonal variation and subsequent temperature changes that are also recognized by circadian clock genes.

The Circadian rhythm greatly influences fundamental homeostatic functions, including: hormone fluctuation, body temperature changes, waking and sleep cycles, REM sleep, immune cytokine signaling, antioxidant systems, mitochondrial oxidative phosphorylation, protein translation, autophagy, and many other fundamental processes (R), (R). Biological systems governed by circadian rhythms are entrained to have ebbs and flows, peaks and valleys that operate through a diurnal rhythm.

Healthy individuals experience oscillatory fluctuations in a number of hormones, nutrients and immune-signaling cytokines in response to the circadian rhythm. The list below is an example of diurnal fluctuation of some biological molecules and hormones, under normal, healthy conditions.

Nighttime

• Increased inflammatory cytokine activity: IL12, TNF-a, IFN-gamma (R)
• Increase in Naive T-cells (R)
• Increase in T-cell proliferation (R)
• Increased Melatonin
• Increased Autophagy and Glymphatic flow
• Reduced expression of anti-inflammatory IL10 (R)
• Increased Growth hormone
• Increased Prolactin
• Reduced Cortisol
• Sympathetic tone reduced/parasympathetic increase
• Peak serum Zinc 6-10pm (R) but low in early morning
• Reduced serum copper but higher in morning (R)
• Lower BDNF, higher in the mornings (R)

Daytime

• Clearance of NK-sensitive tumor cells (R)
• Increase of NK cells in spleen (R)
• Increase in anti-inflammatory IL-10 (R)
• Increase in cytotoxic NK cells (blood) (R)
• Increase in sympathetic/decrease in parasympathetic
• Increase in SCN expression of NGF (nerve growth factor) via P75ntr. Peaks are believed to occur in the early/light/rest phase of the day (R), (R)
• Peaks of BDNF observed in the morning (R)
• Peak in serum copper between 10am-2pm (R)

Life in the modern world is not conducive to the natural rhythms that drive our circadian rhythms. Increased exposure to artificial lighting at night leads to aberrant circadian rhythms and sleep timing (R). While blue light exposure is understood to set the circadian rhythm, chronic exposure, especially at nighttime has deleterious effects on circadian function. Blue light exposure acts to inhibit the expression of the primary BMAL1 circadian gene, and to increase the expression of Cryptochrome 1, as well as to suppress melatonin (R), (R).

In chronic diseases such as Parkinson’s, circadian biology is compromised (R), (R). In Parkinson’s, this can be due in part to the loss of striatal dopamine, as dopamine plays significant roles in biological clock regulation, such as through it’s influence of melanospin in the retina, it’s regulation of clock gene expression in the dorsal striatum, as well as dopamine’s function as an efflux transmitter in the SCN (R). However, the loss of dopaminergic transmission alone cannot explain the etiology of Parkinson’s disease. REM sleep disorders (such as IRBD) are strongly predictive of developing a synucleinopathy, such as Parkinson’s. An ongoing longitudinal research study, beginning in 2016 is currently evaluating IRBD sleep disorders in 102 patients. Preliminary evaluation of IRBD patients has revealed measurable and early changes in the circadian transcription factor BMAL1, along with subtle changes in gait, compared to older controls (R). These initial findings provide strong evidence that disruption to the circadian rhythm are a major etiological driver of Parkinson’s, multiple system atrophy, Lewy body dementia and related synucleinopathies.

SIRT-1 & NAD+ Activate BMAL1/CLOCK Gene Expression

NAD+ dependent SIRT-1 induces the expression of the heterodimeric circadian clock genes BMAL1/CLOCK (R), (R). This triggers the expression of PER (period circadian regulator) and CRY (cryptochrome). When PER and CRY levels peak, this induces a negative feedback inhibition of BMAL1/CLOCK. SIRT-1 also controls the expression and deacetylation of the Per2 (period 2) clock gene, and is critical in CLOCK-mediated chromatin remodeling, (R), (R).

Sirtuins (SIRT’s) are a family of nuclear deacetylase proteins which require NAD+ for activation. Sirtuins play important roles in orchestrating gene expression, antioxidant defense, DNA repair, stem cell differentiation (including neuronal stem cells), circadian clock expression, as well as influencing the balance between neuronal cell survival and cell death (R), (R). In the brain, SIRT-1 modulates synaptic plasticity, dendritic branching, and the elongation of neuronal axons. In Parkinson’s disease, activation of SIRT-1 has been shown to reduce the formation of alpha synuclein, the main protein aggregate associated with disease progression (R). Post mortem studies on Parkinson’s brains have found SIRT-1 to be down-regulated, suggesting this as a major part of the pathophysiology, and as a major therapeutic target (R).

Both BMAL1 and it’s paralog BMAL2, were shown to have significantly reduced expression in Parkinson’s patients in two separate studies (R), (R). It has been demonstrated that BMAL1 expression should function within a diurnal rhythm, with expressions higher during nighttime and sleep. Parkinson’s patients were shown to have lower BMAL1 expression in leukocytes, as measured 4 times in one day, as well as significantly less variation in BMAL1 expression during night and day. Moreover, the relative BMAL1 levels have been shown to correlate with Parkinson’s disease severity (as measured by UPDRS rating scale), illustrating the significance of biological clock regulation in the disease (R).

Fasting, Caloric Restriction & Ketosis Activate SIRT-1

• Ketogenic diets have been proposed to activate SIRT-1 in neurons, partly through ketones’ ability to increase NAD+ levels in the brain (R).
• Caloric restriction, such as fasting has been show to raise SIRT-1 levels in humans. A study performed on 43 men found that 30 days of religious, Ramadan fasting induced a 4.63 fold increase in SIRT-1 mRNA in mononuclear cells, compared to the non-fasting group (R). Additionally, Ramadan fasting (no oral intakes from dawn through sunset) has been show to induce the expression of other critically protective antioxidants, NRF2 and SOD2 (R).

The effect of ketogenic diets and fasting on SIRT-1 activation implies that these may serve as significant therapies in Parkinson’s disease.

Consequences of Circadian Clock Gene Disruption in Parkinson’s

Blood Brain Barrier & The Circadian Clock

The loop circuit of BMAL1/CLOCK/PER/CRY/REV-erb is expressed in most cellular systems of the body. BMAL1 knockout mice (-/-), exhibit hyper-permeability of the blood brain barrier, with concomitant astrocyte activation (R). A leaky blood brain barrier is concerning, because it may lead to higher levels of toxins in the brain. This is alarming, as it has been demonstrated that Parkinson’s patients have higher levels of aluminum in the substantia nigra region of the brain, the caudate nucleus and globus pallidus, compared to controls (R). Moreover pesticide exposure is known to cause signs and symptoms of Parkinson’s disease, and epidemiological studies have identified these associations. This is particularly true of lipophilic pesticides (Rotenone), as well as the widely used herbicide, Paraquat (R), (R). The takeaway from this research is that deficient expression of BMAL1 (known to occur in Parkinson’s) may lead to increased toxins permitted to enter the brain.

NRF2 & The Circadian Clock

In vitro study of macrophages has identified that BMAL1 controls the expression of NRF2. NRF2 is a critical transcription factor that induces the expression of a number of ARE’s (antioxidant response elements), such as glutathione, quinone reductases, thioredoxins, NADPH generation, and iron homeostasis. Immune macrophages lacking sufficient BMAL1 display lower NRF2 expression and glutathione in response to LPS challenge, higher levels of pro-inflammatory IL1ß, and activation of HIF-1α (R).

Mice bred to be devoid of hepatic BMAL1 develop insulin resistance, swollen mitochondria incapable of adaptive responses, and hepatic pathologies. At the same time, a high fat diet rescues BMAL1-deficient mice from these outcomes (R).

NF Kappa-ß & The Circadian Clock

NF kappa-ß is a significant transcription factor with a number of regulatory effects on inflammatory cytokine expression. Through a mouse model, researchers discovered that the intensity of NF kappa-ß expression to a variety of immunomodulators is mediated via the CLOCK gene. In the absence of BMAL1, the intensity of NF kappa ß-expression was increased (R).

Neurotrophic Growth Factors & The Circadian Clock

Growth factors are signaling molecules which play integral roles in wound healing, tissue repair, cell survival, neurological functions, cell differentiation, stem cell activities and immune signaling. Significantly, a critical function of neurotrophins is to activate NRF2 in neurons and astrocytes (R).

Importantly, the brain’s neurotrophins are under circadian control. A study evaluating plasma BDNF levels of 34 healthy males found that BDNF levels were significantly higher in the morning than at night, and levels positively correlated with cortisol rhythm (R). Most if not all neurotrophins are under the regulation of P75ntr, a clock gene controlled via BMAL1/CLOCK (R).

While growth factors hold significant therapeutic potential in Parkinson’s disease, the fact that their endogenous production is circadian controlled, implies a potential use of chronotherapy, i.e. timing therapeutic protocols based upon known circadian peaks and valleys.

Glymphatic Detoxification of Waste From The Brain

The glymphatic system is the brain’s drainage and clearance system. It was first identified in 2012 and has garnered much attention in the realm of complex illness, due to its ability to remove harmful toxins and waste from the brain. The glymphatic system is most operative at nighttime during deep, non-REM sleep. The glymphatic system involves the removal of macro waste from the CNS via the interstitial and cerebrospinal fluids and the perivascular spaces (R).

During phases of the deep sleep cycle, there is a doubling of the clearance of cerebrospinal fluid from the brain, with a 60% increase in the interstitial spaces, compared to waking times (R), (R). Glymphatic flux is correlated with increased slow wave delta power (0-3 Hz) during deep sleep cycles (R).

Glymphatic activation is facilitated locally via astrocytic regulation of extravascular fluids, via aquaporin-4. Glymphatic activation in Parkinson’s is an important area of emerging research, because protein aggregates such as alpha synuclein, as well as higher levels of chemical and heavy metal toxins are found in the Parkinsonian brain (R).

Although the precise mechanisms of circadian clock control of the glymphatic system are not fully understood, these areas are currently being explored in research (R).

Currently, methodologies for glymphatic system evaluation in humans is lacking. Despite this, research has shown that alpha synuclein in the CSF is decreased 13% in Parkinson’s patients (measuring for reduced clearance from the brain), compared to controls. However this methodology has reduced specificity and sensitivity for Parkinson’s, and there is an urgent need to develop new methods of glymphatic evaluation (R).

Light Therapy: As Possible Adjunct To Restore Circadian Clock Function

The use of light therapies for Parkinson’s disease has been explored to some extent, although none of this research has used light therapy in a chronotherapeutic form, and none to date has attempted to study light and dark therapies on the expression of circadian clock genes.

Different wavelengths of light will act differently on biological systems. Preliminary research suggests potential modulation of sleep and mood disorders in Parkinson’s via use of blue light (R). However, blue spectrum light is of concern because of the known inhibitory effects on melatonin, and the fact that melatonin levels in Parkinson’s has found to be lower, particularly during peak nighttime hours (R).

A randomized, controlled trial was conducted on 18 Parkinson’s patients (assigned to either therapy or the sham control group) using NIR (near infrared) LED, 670nm spectrum light. Patients receiving light therapy received 18 treatments, in 6, 1-minute intervals over 9 weeks. This method and light wavelength has been shown to penetrate the substantia nigra region of the brain. Even with this short and limited number of treatment sessions, patients receiving near infrared light therapy displayed improvements in gait speed (R). This research is consistent with other studies, which found that measurable benefits are obtainable using near infrared light therapy in Parkinson’s disease.

Chronotherapeutics & Parkinson’s

It would seem that chronotherapeutics should serve as a core component to Parkinsonian therapeutics, given that the circadian system is dysregulated. Chronotherapy is not a new idea. Traditional medical systems such as TCM (Traditional Chinese Medicine) and Ayurvedic Medicine have long recognized the times of the day and night as key interval phases, of organ, system and dosha functions. Future applications for chronotherapy in Parkinson’s disease envisions precise timing of food, fasting, supplements, drugs, exercise, sleep, wake and rest, with the end goal of re-synchronizing the internal circadian clock.

Moreover, future research studies should consider metabolomic and lipidomic patient testing to be conducted at different intervals throughout the day and night, in order to determine which biological and physiological processes are de-synchronized to the clock. This research is limited by cost at present time, but underscores a need for precision-focussed, circadian-based, biomarker analyses, and treatment.