Subject: CryoNet #25780 - #25781

From: CryoNet <[email-masked]>
Date: 12 Mar 2005 10:00:00 -0000

CryoNet - Sat 12 Mar 2005

    #25780: The cause of presbyopia is not aging [Doug Skrecky]
    #25781: central role for phospholipase D and ceramide in aging? [Doug Skrecky]

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Message #25780
Date: Fri, 11 Mar 2005 20:29:42 -0800 (PST)
From: Doug Skrecky <[email-masked]>
Subject: The cause of presbyopia is not aging

[Instead it is lifelong growth in the thickness of the eye
lens. Greater force is then required to deform the lens
to refocus at short distances. Eventually increases in
muscle strength can no longer keep pace with this increased
load and presbyopia results. There are currently no
eye-drops or similar non-invasive procedures for correcting
this age-associated defect.(sigh)]

Prog Retin Eye Res. 2005 May;24(3):379-93. Epub 2004 Dec 19
The mechanism of presbyopia.
  Accommodation in humans refers to the ability of the lens
to change shape in order to bring near objects into focus.
Accommodative loss begins during
childhood, with symptomatic presbyopia, or presbyopia that
affects one's day to day activities, striking during midlife.
While symptomatic presbyopia has traditionally been treated
with reading glasses or contact lenses, a number of surgical
interventions and devices are being actively developed in an
attempt to restore at least some level of accommodation. This
is occurring at a time when the underlying cause of presbyopia
remains unknown, and even the mechanism of accommodation is
occasionally debated. While Helmholtz' theory regarding the
mechanism of accommodation is generally accepted with regard
to broad issues, additional details continue to emerge.
Age-related changes in anterior segment structures associated
with accommodation have been documented, often through in
vitro and/or rhesus monkey studies. A review of these findings
suggests that presbyopia develops very differently in humans
compared to non-human primates. Focusing on non-invasive in
vivo human imaging technologies, including Scheimpflug
photography and high-resolution magnetic resonance imaging
(MRI), the data suggest that the human uveal tract acts as
a unit in response to age-related increasing lens thickness
and strongly implicates lifelong lens growth as the causal
factor in the development of presbyopia.

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Message #25781
Date: Fri, 11 Mar 2005 20:43:05 -0800 (PST)
From: Doug Skrecky <[email-masked]>
Subject: central role for phospholipase D and ceramide in aging?

[Alas, ceramide also appears to have some anticancer effects as well.]

Biochim Biophys Acta. 1999 Jul 30;1439(2):291-8
Phospholipase D in cellular senescence.
Cellular senescence appears to be an important part of organismal
aging. Cellular senescence is characterized by flattened enlarged
morphology, inhibition of DNA replication in response to growth
factors, inability to phosphorylate the pRb tumor suppressor
protein, inability to produce c-fos or AP-1 and overexpression of
a variety of genes, notably p21 (CIP-1/WAF-1) and p16(INK). It is
now clear that certain early mitotic signals become defective with
the onset of senescence. Among these is the PLD/PKC pathway.
Evidence suggests that activation of PLD and PKC is critical for
mitogenesis. Recent data suggest that the defect in PLD/PKC in
cellular senescence is a result of elevated cellular ceramide
levels which inhibit PLD activation. It appears that the elevated
ceramide is a result of neutral sphingomyelinase activation.
Ceramide acts to inhibit the activation of PLD by possibly three
mechanisms, inhibiting activation by Rho, translocation to the
membrane and gene expression. Addition of ceramide to young cells
not only inhibits PLD but also recapitulates all the standard
measures of cellular senescence as described above.

J Biol Chem. 2001 Jul 6;276(27):24901-10. Epub 2001 May 02.
Role of ceramide in mediating the inhibition of telomerase
activity in A549 human lung adenocarcinoma cells.
   This study was designed to analyze whether ceramide, a
bioeffector of growth suppression, plays a role in the
regulation of telomerase activity in A549 cells. Telomerase
activity was inhibited significantly by exogenous C(6)-ceramide,
but not by the biologically inactive analog dihydro-C(6)-ceramide,
in a time- and dose-dependent manner, with 85% inhibition
produced by 20 microm C(6)-ceramide at 24 h. Moreover, analysis
of phosphatidylserine translocation from the inner to the outer
plasma membrane by flow cytometry and of poly(ADP-ribose)
polymerase degradation by Western blotting showed that ceramide
treatment (20 microm for 24 h) had no apoptotic effects. Trypan
blue exclusion, [(3)H]thymidine incorporation, and cell cycle
analyses, coupled with clonogenic cell survival assay on soft
agar, showed that ceramide treatment with a 20 microm concentration
at 24 h resulted in the cell cycle arrest of the majority of the
cell population at G(0)/G(1) with no detectable cell death. These
results suggest that the inhibition of telomerase by ceramide is
not a consequence of cell death but is correlated with growth
arrest. Next, to determine the role of endogenous ceramide in
telomerase modulation, A549 cells were transiently transfected
with an expression vector containing the full-length bacterial
sphingomyelinase cDNA (b-SMase). The overexpression of b-SMase,
but not exogenously applied purified b-SMase enzyme, resulted in
significantly decreased telomerase activity compared with controls,
showing that the increased endogenous ceramide is sufficient for
telomerase inhibition. Moreover, treatment of A549 cells with
daunorubicin at 1 microm for 6 h resulted in the inhibition of
telomerase, which correlated with the elevation of endogenous
ceramide levels and growth arrest. Finally, stable overexpression
of human glucosylceramide synthase, which attenuates ceramide
levels by converting ceramide to glucosylceramide, prevented the
inhibitory effects of C(6)-ceramide and daunorubicin on telomerase.
Therefore, these results provide novel data showing for the first
time that ceramide is a candidate upstream regulator of telomerase.

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