Alteration of human platelet protein kinase C with normal aging

Phorbol ester mediated activation of inducible nitric oxide synthase results in platelet profilin nitration

Nitric oxide is an important precursor for peroxynitrite production under in vivo conditions leading to cell injury and cell death. In platelets, a number of cytosolic and actin binding proteins were shown to be nitrated [K.M. Naseem, S.Y. Low, M. Sabetkar, N.J. Bradley, J. Khan, M. Jacobs, K.R. Bruckdorfer, The nitration of platelet cytosolic proteins during agonist-induced activation of platelets. FEBS Lett. 473 (1) (2000) 199-122 and M. Sabetkar, S.Y. Low, K.M. Naseem, K.R. Bruckdorfer, The nitration of proteins in platelets: significance in platelet function, Free Radic. Biol. Med. 33 (6) (2002) 728-736]. We investigated the possible mechanism that regulates profilin (an actin binding protein) nitration in platelets. Activation of bovine platelets with arachidonic acid, thrombin, and phorbol 12,13-dibutyrate resulted in nitration of profilin on tyrosine residue. In vivo profilin nitration showed a four- and eight-fold increase in the presence of thrombin and phorbol 12,13-dibutyrate, respectively. Analysis of nitroprofilin levels in the presence of NOS inhibitors (1400W and EGTA), indicated that profilin nitration in phorbol 12,13-dibutyrate treated platelets is mediated by inducible nitric oxide synthase. Phorbol ester treated platelets exhibited higher levels by inducible nitric oxide synthase (491% over control), while total nitric oxide synthase activity increased by 5% over control. Higher levels of peroxynitrite in platelets treated with phorbol 12,13-dibutyrate indicated that profilin nitration is mediated by peroxynitrite. Increase in phosphatidylinositol 3-kinase (PI 3-kinase) activity in platelets treated with thrombin and phorbol 12,13-dibutyrate indicates that nitration of platelet profilin could be mediated by PI 3-kinase. A decrease in the level of nitroprofilin in PDBu treated platelets in the presence of inducible nitric oxide synthase inhibitor, 1400W, was observed suggesting that profilin nitration is mediated by PI 3-kinase dependent activation of inducible nitric oxide synthase.

Age-dependent activation of PKC isoforms by angiotensin II in the proximal nephron

ANG II increases fluid absorption in proximal tubules from young rats more than those from adult rats. ANG II increases fluid absorption in the proximal nephron, in part, via activation of protein kinase C (PKC). However, it is unclear how age-related changes in ANG II-induced stimulation of the PKC cascade differ as an animal matures. We hypothesized that the response of the proximal nephron to ANG II decreases as rats mature due to a reduction in the amount and activation of PKC rather than a decrease in the number or affinity of ANG II receptors. Because PKC translocates from the cytosol to the membrane when activated, we first measured PKC activity in the soluble and particulate fractions of proximal tubule homogenates exposed to vehicle or 10(-10) M ANG II from young (26 +/- 1 days old) and adult rats (54 +/- 1 days old). ANG II increased PKC activity to the same extent in homogenates from young rats (from 0.119 +/- 0.017 to 0.146 +/- 0.015 U/mg protein) (P < 0.01) and adult rats (from 0.123 +/- 0.020 to 0.156 +/- 0.023 U/mg protein) (P < 0.01). Total PKC activity did not differ between groups (0.166 +/- 0.018 vs. 0.181 +/- 0.023). We next investigated whether activation of the alpha-, beta-, and gamma-PKC isoforms differed by Western blot. In homogenates from young rats, ANG II significantly increased activated PKC-alpha from 40.2 +/- 6.5 to 60.2 +/- 9.5 arbitrary units (AU) (P < 0.01) but had no effect in adult rats (46.1 +/- 5.1 vs. 48.5 +/- 8.2 AU). Similarly, ANG II increased activated PKC-gamma in proximal tubules from young rats from 47.9 +/- 13.2 to 65.6 +/- 16.7 AU (P < 0.01) but caused no change in adult rats. Activated PKC-beta, however, increased significantly in homogenates from both age groups. Specifically, activated PKC-beta increased from 8.6 +/- 1.4 to 12.2 +/- 2.1 AU (P < 0.01) in homogenates from nine young rats and from 19.0 +/- 5.5 to 25.1 +/- 7.1 AU (P < 0.01) in homogenates from 12 adult rats. ANG II did not alter the amount of soluble PKC-alpha, -beta, and -gamma significantly. The total amount of PKC-alpha and -gamma did not differ between homogenates from young and adult rats, whereas the total amount of PKC-beta was 59.7 +/- 10.7 and 144.9 +/- 41.8 AU taken from young and adult rats, respectively (P < 0.05). Maximum specific binding and affinity of ANG II receptors were not significantly different between young and adult rats. We concluded that the primary PKC isoform activated by ANG II changes during maturation.

Signal transduction in LPS-activated aged and young monocytes

Aged monocytes, that is, monocytes purified from the blood of donors > or =65 years of age, when compared with young monocytes, that is, monocytes purified from the blood of young donors 25 years of age, display a decrease in interleukin-6 (IL-6) and tumor necrosis factor (TNF) production after activation by lipopolysaccharide (LPS). The LPS concentration required to obtain IL-6 and TNF production is much higher for aged monocytes than for young monocytes. Furthermore, the intensity of TNF and IL-6 production was much weaker for LPS-activated aged monocytes than for LPS-activated young monocytes. In addition, deficient protein kinase C (PKC)-alpha, PKC-/betaI, and PKC-betaII activation, deficient mitogen-activated protein kinase (MAP-Kinase) activation, and deficient expression of c-Fos and c-Jun was observed in LPS-activated aged monocytes when compared with LPS-activated young monocytes. These data suggest that age induces human monocyte immune deficiencies that could be observed not only at the functional level but also in the signal transduction pathways.

Age-dependent increases in protein kinase C-alpha beta immunoreactivity and activity in the human brain: possible in vivo modulatory effects on guanine nucleotide regulatory G(i) proteins

In the postmortem human brain (20 specimens of frontal cortex, Brodmann area 9) the abundance of immunoreactive protein kinase C (PKC-alpha beta) and the activity of PKC (calcium, phosphatidylserine, and phorbol ester-dependent enzymes) were determined to study the effect of aging (range 1 month to 89 years) on this regulatory enzyme. Also, the abundance of immunoreactive G protein subunits (G alpha i1/2, G alpha i3, G alpha o, G alpha s and G beta) were assessed in parallel to investigate possible relationships with PKC-alpha beta. The abundance of PKC-alpha beta was positively correlated with aging (r = 0.62, n = 20, P < 0.005). Moreover, PKC activity also showed a significant positive correlation with the age of the subject at death (r = 0.55, n = 14, P < 0.05). Because of the known in vitro modulatory role of PKC-alpha beta on G(i) proteins, the existence of an in vivo effect of brain PKC-alpha beta on various G proteins was assessed through correlation analyses. In the brain of the same subjects, there were significant negative correlations between the immunoreactivity of PKC-alpha beta and the immunoreactivities of G alpha i1/2 (r = -0.78, n = 13, P < 0.005) and G alpha i3 (r = -0.58, n = 15, P < 0.005). In the same brains, similar negative, although non-significant, correlations were found between the levels of PKC-alpha beta and those of G alpha o, G alpha s and G beta. The results demonstrate an up-regulation of brain PKC-alpha beta with aging and suggest the existence of a relevant in vivo modulatory role of this regulatory enzyme on inhibitory Gi proteins in the human brain during the process of aging.

Cellular distribution of protein kinase C isozymes in CD3-mediated stimulation of human T lymphocytes with aging

Protein kinase C (PKC) is involved in a variety of cellular responses, such as the expression and secretion of IL-2, the regulation of cytotoxic killing and cell proliferation. It is known that these immune functions are altered with aging. Here, we show that anti-CD3-triggered T cell proliferation is significantly decreased with aging and that H7, an inhibitor of PKC, impairs the anti-CD3-induced T cell proliferation in a differential manner, lymphocytes of healthy young subjects being more sensitive to the PKC inhibitor than those of elderly subjects. We examined (Western blot) the presence and the cellular distribution of PKC isozymes in T lymphocytes of healthy young and elderly subjects in the resting state and after anti-CD3 mAb stimulation using antibodies directed against PKC alpha, beta, delta, epsilon and zeta isoforms in the cytosol and the plasma membrane fractions. These five PKC isotypes were present in human T cells of young and elderly subjects. However, their distribution between the cytosolic and membrane fractions varied according to the isozymes and the age of the subjects. In resting lymphocytes of young subjects, all the PKC isozymes were found in the cytosolic fraction, except PKC-zeta. In resting lymphocytes of elderly subjects PKC-zeta and -epsilon were almost equally distributed between the cytosolic and the membrane fractions, whereas PKC-alpha and -zeta were mainly found in the membrane fraction and PKC-beta was almost exclusively located in the cytosolic fraction. The translocation of PKC-alpha, -beta, -delta and -epsilon could be observed under anti-CD3 mAb stimulation in lymphocytes of young subjects, while in the case of elderly subjects only the PKC beta isoform was translocated. Our results suggest tha the decreased availability of cytosolic PKC may contribute to the diminished PKC-dependent responses to CD3-triggered stimulation of human T lymphocytes with aging.

Changes in platelet phospholipase C protein level and activity in Alzheimer's disease

We have previously demonstrated that PLC-delta was abnormally accumulated in autopsied brains with Alzheimer's disease (AD). As nonneuronal tissue involvement in AD is also suggested and PLC activity is reduced in AD platelets, we examined the changes of the protein level of PLC-delta and its enzyme activity in platelets taken from patients with AD and age-matched controls. PLC-delta in human platelets was detected as a 72 kDa protein using a specific antibody against PLC-delta. Western blots revealed that the protein level of PLC-delta was significantly higher in the cytosolic fraction prepared from AD platelets compared to controls. We investigated the activity of PLC-delta which hydrolyzes phosphatidylinositol and found that the PLC-delta activity in the cytosolic fraction from AD platelets was significantly reduced compared to the control. This finding that the enzyme activity per PLC-delta molecule is reduced in AD platelets is consistent with the study using Alzheimer brains. These results suggest that aberrant phosphoinositide metabolism is present in nonneuronal tissues as well as the brains of patients with AD.

Platelet protein kinase C levels in Alzheimer's disease

Alzheimer's disease (AD) has been suggested to be a systemic disease, and signal transduction abnormalities have been reported in non-neuronal AD cells. We have previously quantified the protein kinase C (PKC) subtypes in AD and control brains using a two-site enzyme immunoassay (EIA), and have shown that type II PKC levels were significantly reduced in the temporal cortex of AD patients. In this study, we used this EIA to assess the platelet levels of type II PKC in age-matched groups of AD patients and normal controls. The cytosolic level of type II PKC was significantly higher in AD platelets than in control platelets but was unchanged in the membranous fraction. Platelet proteins showed no differences between the AD and control groups. Therefore, the type II PKC content of the cytosolic fraction was increased in AD platelets. These results suggest that type II PKC may be altered in both the brain and platelets of AD patients and support the hypothesis that AD is a systemic disease.