Summary: The Ph4-tm gene has been implicated in fear and anxiety. P4h-tm knockout mice showed a diminished response to fear and showed more courageous behavior than wild-type mice with a functional P4h-tm gene.
Source: University of Eastern Finland
Finnish researchers at the University of Eastern Finland and the University of Oulu have discovered of a new type of gene mutation that reduces fear and anxiety, and increases social interaction. The researchers employed gene manipulation technology to remove the P4h-tm gene from the mouse genome and found an unexpected change in mouse behaviour. P4h-tm knockout mice showed striking courage and a lack of learned helplessness compared to congenic wild-type mice with a functional P4h-tm gene. The results were published in Neuropharmacology.
The researchers assessed the mice with a large behavioural test battery that included a novel type of test for the panic reaction. The mice were placed in an air-tight box that was first filled up with regular room air, then with 10% carbon dioxide. An elevated concentration of carbon dioxide induces an innate freezing reaction that is thought to resemble the feeling of suffocation in patients suffering from panic attacks. P4h-tm knockout mice displayed substantially less freezing than control mice in response to carbon dioxide exposure. In tests for social interaction, P4h-tm knockout mice made clearly more contact with another mouse than the controls. In addition, behavioural tests routinely used for screening antianxiety and antidepressant drugs revealed reduced fear, anxiety and learned helplessness in P4h-tm knockout mice. Further, the study found a connection between brain anatomy and the behavioural phenotype: the expression of the P4h-tm gene was especially high in the amygdala that plays a key role in controlling emotional reactions, including fear and anxiety.
The P4h-tm gene accounts for the transcription of the P4H-TM protein. This protein belongs to the family of prolyl-4-hydroxylases that play a pivotal role in the cellular adaptation to a sudden lack of oxygen. However, the P4H-TM protein differs from other prolyl-4-hydroxylases in both its structure and unusual location (endoplasmic reticulum). The physiological role of the P4H-TM protein remains elusive despite years of intensive research, but it is assumed to have other effects on cellular biology besides adaptation to varying oxygen levels. The researches also tested the inactivation of three other known prolyl-4-hydroxylases in separate mouse lines. These mice did not show abnormal behaviour in the above-mentioned tests.
“Our findings are really interesting, but based on a recent international study led by the University of University, we know that the deficiency of the P4H-TM gene results in severe developmental defects in humans,” Professor Heikki Tanila from the University of Eastern Finland notes and continues: “However, in light of present knowledge, we cannot tell whether these harmful effects arise from embryonal development or whether they would also appear if the function of the P4H-TM protein was inhibited in the adult age.”
“We could best find an answer to this question by using conditional gene inactivation in which the gene could be turned off at any desired age,” Dr Henri Leinonen, the first author of the article, concludes.
“In an ideal experiment, P4h-tm would be turned off only in the amygdala of an adult mouse,” Dr Leinonen adds.
Although the striking effect of P4h-tm gene knockout on the emotional reactions of mice is still far away from therapeutic application, it can before long lead to the discovery of neurochemical mechanisms that regulate emotions, and can help to develop novel antianxiety and antidepressant drugs. Anxiety disorders and depression are a huge global problem. According to the World Health Organization (WHO), almost 300 million individuals worldwide suffer from anxiety disorders, and over 300 million suffer from depression.
University of Eastern Finland
Heikki Tanila – University of Eastern Finland
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Original Research: Closed access
“Null mutation in P4h-tm leads to decreased fear and anxiety and increased social behavior in mice”. Heikki Tanila et al. Neuropharmacology. doi:10.1016/j.neuropharm.2019.04.023
Null mutation in P4h-tm leads to decreased fear and anxiety and increased social behavior in mice
HIF prolyl 4-hydroxylases (HIFP4Hs, also known as PHDs and EGLNs) are crucial enzymes that modulate the hypoxia inducible factor (HIF) response and help to maintain cellular oxygen homeostasis. This function is especially well-known for cytoplasmic or nuclear enzymes HIFP4H-1–3 (PHDs 1–3, EglNs 2, 1 and 3, respectively), but the physiological role is still obscure for a fourth suggested HIFP4H, P4H-TM that is a transmembrane protein and resides in the endoplasmic reticulum. Recently however, both experimental and clinical evidence of the P4H-TM involvement in CNS physiology has emerged. In this study, we first investigated the expression pattern of P4H-TM in the mouse brain and found a remarkably selective abundance in brains areas that are involved in social behaviors and anxiety including amygdala, lateral septum and bed nucleus of stria terminalis. Next, we performed behavioral assays in P4h-tm−/− mice to investigate a possible phenotype associated to these brain areas. In locomotor activity tests, we found that P4h-tm−/− mice were significantly more active than their wild-type (WT) littermate mice, and habituation to test environment did not abolish this effect. Instead, spatial learning and memory seemed normal in P4h-tm−/− mice as assessed by Morris swim task. In several tests assessing anxiety and fear responses, P4h-tm−/− mice showed distinct courageousness, and they presented increased interaction towards fellow mice in social behavior tests. Most strikingly, P4h-tm−/− mice practically lacked behavioral despair response, a surrogate marker of depression, in forced swim and tail suspension tests. Instead, mutant mice of all other Hif-p4h isoforms lacked such a behavioral phenotype. In summary, this study presents a remarkable anatomy-physiology association between the brain expression of P4H-TM and the behavioral phenotype in P4h-tm−/− mice. Future studies will reveal whether P4H-TM may serve as a novel target for anti-depressant and anti-anxiety pharmacotherapy.