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

PKCα: Prospects in Regulating Insulin Resistance and AD

Protein kinase C alpha (PKCα) is known to participate in various signaling pathways due to its ubiquitous and dynamic characteristics. Previous studies report that PKCα abrogates peripheral insulin resistance, and recent publications show that it takes part in regulating Alzheimer's disease (AD). Based on evidence in the literature, we have highlighted how many of the substrates of PKCα in its signal transduction cascades are common in AD and diabetes and may have the capability to regulate both diseases simultaneously. Signaling pathways crosslinking these two diseases by PKCα have not been explored. Understanding the complexities of PKCα interactions with common molecules will deepen our understanding of its regulation of relevant pathophysiologies and, in the future, may broaden the possibility of using PKCα as a therapeutic target.

Purinergic dysregulation causes hypertensive glaucoma-like optic neuropathy

Glaucoma is an optic neuropathy characterized by progressive degeneration of retinal ganglion cells (RGCs) and visual loss. Although one of the highest risk factors for glaucoma is elevated intraocular pressure (IOP) and reduction in IOP is the only proven treatment, the mechanism of IOP regulation is poorly understood. We report that the P2Y6 receptor is critical for lowering IOP and that ablation of the P2Y6 gene in mice (P2Y6KO) results in hypertensive glaucoma-like optic neuropathy. Topically applied uridine diphosphate, an endogenous selective agonist for the P2Y6 receptor, decreases IOP. The P2Y6 receptor was expressed in nonpigmented epithelial cells of the ciliary body and controlled aqueous humor dynamics. P2Y6KO mice exhibited sustained elevation of IOP, age-dependent damage to the optic nerve, thinning of ganglion cell plus inner plexiform layers, and a reduction of RGC numbers. These changes in P2Y6KO mice were attenuated by an IOP lowering agent. Consistent with RGC damage, visual functions were impaired in middle-aged P2Y6KO mice. We also found that expression and function of P2Y6 receptors in WT mice were significantly reduced by aging, another important risk factor for glaucoma. In summary, our data show that dysfunctional purinergic signaling causes IOP dysregulation, resulting in glaucomatous optic neuropathy.

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.

Altered brain protein kinase C in depression: a post-mortem study

[(3)H]Phorbol 12,13-dibutyrate (PDBu) binding was measured in soluble and particulate fractions of frontal cortex and hippocampus from suicides, with a firm retrospective diagnosis of depression, and individually matched controls. Suicides were divided into those who had been free of antidepressant drugs for at least 3 months and those in whom prescription of antidepressants was clearly documented. In frontal cortex, there was a significantly higher number (by 75%) of [(3)H]PDBu binding sites in the soluble fraction in antidepressant-free suicides compared to controls; significant differences were also seen in the proportion of sites in the soluble and particulate fractions. Higher numbers of [(3)H]PDBu binding sites in the particulate fraction of hippocampus in antidepressant-free suicides was restricted to those who died by violent means. No significant differences in the number of [(3)H]PDBu binding sites were found in antidepressant-treated suicides compared to controls. This study provides evidence for the involvement of protein kinase C in the pathophysiology of depression.

Expression of adhesion molecules and G proteins in circulating neutrophils in chronic obstructive pulmonary disease

We investigated the expression of adhesion molecules in circulating neutrophils (lymphocyte function-associated antigen-1 [LFA-1], Mac-1, and L-selectin) and endothelial cells (soluble intercellular adhesion molecule-1[sICAM-1]) in 23 patients with stable chronic obstructive pulmonary disease (COPD), 18 subjects with exacerbated COPD, and 23 healthy volunteers. Also, in these circulating neutrophils, we assessed the expression of two G protein subunits (Galphas and Galphai1/2). Compared with control subjects, patients with stable COPD showed increased expression of Mac-1 (p < 0.001) and lower levels of sICAM-1 (p = 0.002); LFA-1 and L-selectin expression was similar in patients and control subjects. During exacerbations, compared with stable patients, the expression of Mac-1 and LFA-1 was reduced (p < 0.001). Finally, the expression of Galphas (but not Galphai1/2) was also reduced (p < 0.001) in circulating neutrophils of patients with COPD, irrespective of the clinical condition of the patient. These results indicate that in patients with COPD: (1) the expression of some neutrophil adhesion molecules (Mac-1) is abnormal, and that this pattern changes during exacerbations; (2) there may be a form of endothelial dysfunction, as suggested by the low sICAM-1 levels; (3) the expression of G protein subunit (Galphas) in circulating neutrophils is downregulated, irrespective of their clinical conditions. Overall, these results indicate the presence of significant systemic abnormalities in COPD.

Changes in the expression of protein kinase C (PKC), phospholipases C (PLC) and D (PLD) isoforms in spleen, brain and kidney of the aged rat: RT-PCR and Western blot analysis

The age-dependent changes of expression of protein kinase C (PKC), phospholipase C (PLC) and phospholipase D (PLD) isozymes were analyzed in spleen, brain and kidney of young-adult (12-16 week-old) and aged (82-88 week-old) rats. The activities of spleen cPKC and nPKC were significantly decreased by nearly 35 and 30% in aged rats compared to those of young adults, respectively (P < 0.05). The level of PKC beta1 was significantly decreased in aged rats as assessed by RT-PCR and Western blot analyses. In aged rat brain where the activity of cPKC was significantly decreased by nearly 25% (P < 0.05), PKC alpha and beta1 isozymes were significantly down-regulated. In kidney, the level of PKC beta2 was decreased. In spleen the both mRNA and protein levels of PLC beta2 and gamma2 were significantly down-regulated in aged rat (P < 0.05). PLC beta1 was also significantly lower in aged rat brain (P < 0.05) as assessed by RT-PCR and Western blotting. Moreover, PLC beta1 was significantly down-regulated in both mRNA and protein levels in aged rat kidney (P < 0.05). In contrast, the tissues examined, the expressions of PLD isozymes (PLD1a, 1b and 2) were rather stable in the course of aging. These results indicate that mRNAs of PLD isozymes were rather stable but that particular PKC and PLC isozymes were down-regulated in different tissues during aging, suggesting age-dependent decline of specific PKC and PLC isozymes in organs which may, at least in part, be implicated in tissue dysfunction with aging.