Circadian Clock Genes and Immune T-Cell Functions

Zhong Sheng Sun

Weill Medical College of Cornell University

Funded in June, 2002: $300000 for 3 years
LAY SUMMARY . ABSTRACT . FINDINGS . SELECTED PUBLICATIONS .

ABSTRACT

back to top

Circadian Clock Genes and Immune T-Cell Functions

Accumulated evidence indicates that the circadian clock exists and functions in many peripheral tissues, including immune tissues and cells, though the details of the nature of the immune clocks and their relationship to central clock in the suprachiasmatic nucleus (SCN) is not well understood. Following our recent discovery of circadian expression of circadian clock genes, per1-3, in human and mPer1 and interlukine-2 (mIL-2) in mouse peripheral blood mononuclear cells, we hypothesize that 1) the circadian clock genes will prove to be important to immune functioning in health and disease. and 2) the clock regulatory mechanism in immune cells is regulated in part by SCN central clock through circadian signaling molecules, but functions as cell autonomous in certain extent. The proposed study is to test these hypotheses and provides insights into feature of immune clock system and brain-immune clock interactions.

The Specific Aims of this application are:

1. To investigate if there is autonomous immune clock by using in vivo approach. We will identify the defects in clock genes by comparing profiles of clock genes in immune tissues or cell from both wild-type and mPer1-/-/mPer2-/- double mutant strains, respectively. Then, these profiles will be used to compare with the ones derived from one strain of tissue-specific mutant mice, which is generated from bone marrow transplantation and carries with normal immune clock but mutated SCN clock (SCN-mPer1 -/-/mPer2-/-). If the restoration of rhythmicity of circadian clock genes in SCN-mPer1-/-/mPer2-/- were observed, it would suggest the autonomy of immune clock.

2. To elucidate the role of circadian clock in immune T cell function. We will measure the profiles of several immune regulatory genes, such as IL-2, TNFa, IL-12, INF-r, and IL-4 in different mouse strains which are under both constant darkness and dark/light cycle. Because we have collected the serum from mouse blood, the profile of cytokine (IL-1b, TNFa, IN-12, IL-4) will also been measured. The alteration of phase and amplitude in any one of immune regulatory genes would indicate a role of the circadian clock genes in regulating immune functioning. We will transplant BM cells from the mper1-/-/mper2-/- KO mice into normal mice to generate an Immune-mPer1-/-/mPer2-/- mutant mice to see if the observed oscillation of immune regulatory genes in wild-type mice is resulted from immune clock in the immune cells/tissues only or from the signals generated from SCN clock. Finally, we will employ in vitro approach to further identify how the clock genes regulate immune T cell functions, such as their ability to proliferate in response to mitogenic stimulation, to produce cytokines, and to differentiate into effector cells (Type I and Type II) under the influence of cytokines (IL-12 and IL-4).

The proposed studies, which will be conducted jointly as a cooperative venture by a molecular neurobiological laboratory and immunological laboratories, will extend our knowledge of immune clocks and their impact on immune physiology.

FINDINGS

back to top

Lay Results:
Understanding the nature of the clock in immune system and its role in immune regulation is critical for advancement of knowledge of immune function that can be used to inform therapeutic efforts. Because cytokines that are produced by lymphocytes and macrophages are potent mediators of immune responses and the level of individual cytokines can determine immune effector mechanisms, understanding immune-circadian control of specific immune mechanisms, perhaps especially those of the innate immune system, may have important clinical applications, such as the optimization of treatment for patients with acute infection and autoimmune and hematological diseases. As toxicity and anti-tumor efficiency of many traditional cytotoxic drugs in cancer therapy vary significantly depending on the time of day of drug administration, analysis of the circadian organization of physiological immune function might not only provide a better insight into the immune system in general, but can also offer reduction in bone marrow toxicity, as well as increased intensity and improved efficiency for cancer patients. In addition, treatment of acute infection and mass immunization against agents of bioterorrism could be influenced by the immune-circadian clock.

Scientific Results:
We found that Per2-deficient mice were more resistant to lipopolysaccharide (LPS)-induced endotoxic shock than control wild-type mice. We further demonstrate that the levels of the proinflammatory cytokines gamma interferon (IFN-γ) and interleukin-1β (IL-1β) in the serum were dramatically decreased in Per2-deficient mice following LPS challenge, while production of tumor necrosis factor alpha, IL-6, and IL-10 was approximately normal, compared to that in control wild-type mice. Flow cytometric analyses confirmed that the cellularity of most of the immune cell subsets in the spleens of LPS-challenged mice was normal and that the impaired IFN-γ production in Per2-deficient mice was attributable to defective NK and NKT cell function. Our data suggest that Per2 is an important regulator of NK cell function, therefore providing the first direct link between the circadian clock system and innate immune responses.

SELECTED PUBLICATIONS

back to top

Liu J., Malkani G., Shi X., Meyer M., Cunningham-Runddles S., Ma X., and Sun Z.S.  The circadian clock period 2 gene regulates gamma interferon production of NK cells in host response to lipopolysaccharide-induced endotoxic shock. Infect Immun. 2006 Aug;74(8):4750-6.