According to the World Health Organization, more than 21 million people worldwide suffer from schizophrenia, a severe psychiatric disorder that can cause delusions and hallucinations and lead to increased risk of suicide.
Although psychiatric disorders have a genetic component, it is known that environmental factors also contribute to disease risk. There is an especially strong link between psychiatric disorders and complications during gestation or birth, such as prenatal bleeding, low oxygen or malnutrition of the mother during pregnancy.
In the new study, the researchers studied one particular known risk factor: bleeding in the brain, called fetal cerebral hemorrhage, which can occur in utero and in premature babies and can be detected via ultrasound.
In particular, the researchers wanted to examine the role of a lipid called lysophosphatidic acid (LPA), which is produced during hemorrhaging. Previous studies had linked increased LPA signaling to alterations in architecture of the fetal brain and the initiation of hydrocephalus (an accumulation of brain fluid that distorts the brain). Both types of events can also increase the risk of psychiatric disorders.
“LPA may be the common factor,” said Beth Thomas, an associate professor at TSRI and co-author of the new study.
Mouse Models Show Symptoms
To test this theory, the research team designed an experiment to see if increased LPA signaling led to schizophrenia-like symptoms in animal models.
Hope Mirendil, an alumna of the TSRI graduate program and first author of the new study, spearheaded the effort to develop the first-ever animal model of fetal cerebral hemorrhage. In a clever experimental paradigm, fetal mice received an injection of a non-reactive saline solution, blood serum (which naturally contains LPA in addition to other molecules) or pure LPA.
Ten weeks after the mice were born, they were tested for schizophrenia-like symptoms. The researchers found that female mice given LPA-containing serum or LPA alone displayed hyperactivity upon stimulation, showed anxiety and had increased numbers of dopamine-producing neurons—all which are characteristic of schizophrenia and other psychiatric disorders.
The real litmus test to show if these symptoms were specific to psychiatric disorders, according to Mirendil, was the “prepulse inhibition test,” which measures the “startle” response to loud noises. Most mice—and humans—startle when they hear a loud noise. However, if a softer noise (known as a prepulse) is played before the loud tone, mice and humans are “primed” and startle less at the second, louder noise. Yet mice and humans with symptoms of schizophrenia startle just as much at loud noises even with a prepulse, perhaps because they lack the ability to filter sensory information.
Indeed, the female mice injected with serum or LPA alone startled regardless of whether a prepulse was placed before the loud tone.
Next, the researchers analyzed brain changes, revealing schizophrenia-like changes in neurotransmitter-expressing cells. Global gene expression studies found that the LPA-treated mice shared many similar molecular markers as those found in humans with schizophrenia. To further test the role of LPA, the researchers used a molecule to block only LPA signaling in the brain.
This treatment prevented schizophrenia-like symptoms.
Implications for Human Health
This research provides new insights, but also new questions, into the developmental origins of psychiatric disorders.
For example, the researchers only saw symptoms in female mice. Could schizophrenia be triggered by different factors in men and women as well?
“Hopefully this animal model can be further explored to tease out potential differences in the pathological triggers that lead to disease symptoms in males versus females,” said Thomas.
In addition to Chun, Thomas and Mirendil, authors of the study, “LPA signaling initiates schizophrenia-like brain and behavioral changes in a mouse model of prenatal brain hemorrhage,” were Candy De Loera of TSRI; and Kinya Okada and Yuji Inomata of the Mitsubishi Tanabe Pharma Corporation.
This research was supported by the National Institutes of Health (grants TL1 RR025772, R25 GM083275, R01 MH051699, NS084398 and R56 NS082092)
For more information on this article, see http://www.nature.com/tp/journal/v5/n4/full/tp201533a.html. For more information on LPA signaling, see the Chun lab’s recent review article “Lysophosphatidic Acid Signaling in the Nervous System” in the journal Neuron and “Lysophosphatidic acid signalling in development” in the journal Development.
Source: The Scripps Research Institute