Functionally Relevant Differences in Plasma Fatty Acid Composition and Expression of Cytotoxic and Inhibitory NK Cell Receptors between Healthy Young and Healthy Elder Adults

Abstract

(1) Background: In the healthy ageing, NK cell number is not modified; however, their spontaneous cytotoxicity decreases. We postulated that the age-dependent decline in metabolic activities might be responsible for this effect. (2) Methods: The fatty acid profile of 30 healthy young males (23 ± 4 years old, BMI 22.1 ± 1.3) and 30 older males (63 ± 5 years old, BMI 22.9 ± 2.5) donors were evaluated along with the expression of killing (KR) and inhibitory NK receptors (KIR) at basal level and after cultivation with fatty acids for 24 h. (3) Results: Significantly higher levels of oleic (p < 0.01), arachidonic (p < 0.001), lignoceric (p < 0.001), and nervonic acids (p < 0.0001) and significantly lower levels of docosapentaenoic and docosahexaenoic acids (p < 0.01) were found in elders as compared to young adults. At basal levels, significant (p < 0.005) differences in KR and KIR expression were encountered; 12/16 antigens. Treatment of cells with saturated fatty acids or arachidonic acid (AA) significantly enhanced KR expressions (p < 0.001). AA treatment decreased inhibitory KIR expression while docosahexaenoic, and eicosapentaenoic acid increased them. (4) Conclusions: Changes in fatty acids blood levels, and KR and KIR expression in NK cell, are age-dependent. Supplementation of NK cells with eicosapentaenoic or docosahexaenoic acid enhanced inhibitory KIR receptors' expression which may improve their cell function.

Keywords: ageing; killing activating receptors; killing inhibitory receptors (KIR); natural killer cells; saturated fatty acids; unsaturated fatty acids.

Figure 1

Effect of fatty acids treatment on the mean percentage expression of CD94, NKG2A, NKG2D and CD158a antigens. NK cells purified from the blood of the healthy young adults (23 ± 4 years old) and healthy elders (63 ± 5 years old) were treated with 10 µg/mL concentration of the following fatty acids for 24 h. The expression of the receptors was assessed by flow cytometry. The results represent the percentage mean and SD for each group (n = 30). The treatments were compared by one way ANOVA. Bonferroni significance post-test are represented. * p < 0.01, ** p < 0.001 and *** p < 0.0001. No significant differences are recorded for CD94. The mean channel fluorescent intensity (MFI) is represented in Supplementary Figure S3.

Figure 2

Effects of fatty acids on the expression of CD158 antigens in NK cells. The receptors are inhibitory except for CD158i. NK cells purified from the blood of the healthy young adults (23 ± 4 years old) and healthy elders (63 ± 5 years old) were treated with 10 µg/mL concentration of the following fatty acids for 24 h. The expression of the receptors was assessed by flow cytometry. The results represent the percentage mean and SD for each group (n = 30). Treatments were compared by one way ANOVA. Bonferroni significance post-test are represented. * p < 0.01, ** p < 0.001 and *** p < 0.0001. The mean channel fluorescent intensity (MFI) is represented in Supplementary Figure S3.

Figure 3

Expression of NKp30, 44 and 46 and CD160 upon treatment with fatty acids and assessed by flow cytometry. NK cells purified from the blood of the healthy young adults (23 ± 4 years old) and healthy elder (63 ± 5 years old) volunteers were treated with 10 µg/mL concentration of the following fatty acids for 24 h. The expression of the receptors was assessed by flow cytometry. The results represent the percentage mean and SD for each group (n = 30). The treatments were compared by one way ANOVA. Bonferroni significance post-test are represented. * p < 0.01, ** p < 0.001 and *** p < 0.0001. The mean channel fluorescent intensity (MFI) is represented in Supplementary Figure S4.

Figure 4

Expression of CD11b, CD62L, CD69 and CD161, markers of cells activation, upon treatment of NK cells with fatty acids. NK cells purified from the blood of the healthy young (23 ± 4 years old) and healthy elder (63 ± 5 years old) volunteers were treated with 10 µg/mL concentration of the following fatty acids for 24 h. The expression of the receptors was assessed by flow cytometry. The results represent the percentage mean and SD for each group (n = 30). The treatments were compared by one way ANOVA. Bonferroni significance post-test are represented. * p < 0.01, ** p < 0.001 and *** p < 0.0001. The mean channel fluorescent intensity (MFI) is represented in Supplementary Figure S4.

Figure 5

Effect of saturated (SFA) and w9 monosaturated fatty acids (MUFA) on the expression of different antigens in NK cells from healthy young adults and healthy elder subjects. The arrows indicate an increase or decrease of the antigens. SA corresponds to saturated fatty acids, w9 to OA and NA.

Figure 6

Schematic illustration of the effect of arachidonic acid (AA) and PUFA, polyunsaturated (PUFA) w3 fatty acids (DHA and EPA) on the expression of different antigens in NK cells from healthy young adults and healthy elder volunteers. The arrows indicate an increase or decrease of the antigens. AA corresponds to arachidonic acid, and w3 corresponds to DHA and EPA.

Figure 7

Graphical summary of the effect of fatty acid treatment on NK cell receptors in healthy young adults and elder subjects. The red, bar-headed, arrows indicate a decrease in the expression of receptors on NK cells. The green arrows indicate an increase in receptor expression. Receptors are classified as “activating receptors” in green, “activating and inhibitory receptors” in yellow and “inhibitory receptors” in red. Saturated fatty acids are shown in red. Unsaturated fatty acids are shown in blue.

Figure 8

Graphical summary of the effects of fatty acids on NK cells. The postulated effects of saturated (SFA), monounsaturated fatty acids, w9 (MUFA) and polyunsaturated w3, fatty acids (PUFA). The effect of AA, not represented in the picture. FFAR4 corresponds to Free Fatty Acid Receptor 4, β arr-2 corresponds to β arrestin 2, PKC corresponds to Ptotein Kinase C, TAB-1 corresponds to Transforming growth factor beta-activated kinase 1(TAK)-binding protein 1, IIKB corresponds to Inhibitor Of Nuclear Factor Kappa B Kinase Subunit Beta, NFκB corresponds to Nuclear Factor Kappa B transcription factor, MKK4 corresponds to Mitogen-activated protein kinase (MAPK) kinase 4, JNK corresponds to c-Jun N-terminal kinase, Δψm corresponds to The mitochondrial membrane potential and ROS corresponds to Reactive Oxygen Species.