Genetic Activation of the Osmotic Stress Response, but Not Insulin-
Like Growth Factor Signaling, Confers Specific Protection Against
Stress-Induced Aggregation. Reduced signaling of the insulin/insulin-
like growth factor (IGF) pathway protects C. elegans from
several environmental stressors, including hyperosmotic stress
(25, 27, 33). Protection against hyperosmotic stress depends on
the activity of several protein chaperones that are up-regulated
by the FOXO transcription factor daf-16 (33). Such protection
could occur either by preventing the formation of osmotically
induced protein aggregates or by mitigating the physiological
effects of such aggregates. To distinguish between these possibilities,
we crossed the daf-2(e1370) mutant, which causes constitutive
FOXO signaling and protects against hyperosmotic
stress, into the threshold-length polyQ lines. We confirmed that
in these polyQ backgrounds, daf-2(e1370) still activates DAF-16/
FOXO signaling (i.e., formation of dauer larvae at the restrictive
temperature) and provides protection against hyperosmotic
stress [increased 24-h survival on 500 mM NaCl (33)]. The daf-2
(e1370) mutation had no effect on osmotically induced polyQ
aggregate formation in muscle (Fig. S7), and caused only
a modest delay in the kinetics of osmotically induced aggregate
formation in the intestine (Fig. 5 A and B). By contrast, daf-2
mutants exhibit a substantial reduction in the formation of
intestinal age-induced polyQ aggregates (Fig. S6). Therefore,
a reduction in IGF signaling strongly attenuates the formation
of aging-induced Q44-YFP aggregates but has substantially
weaker effects on the formation of osmotically induced
Q44-YFP aggregates.
Another signaling pathway that protects C. elegans from
hyperosmotic stress is the osmotic stress resistance (Osr) pathway
(17, 34–36). Previously, we and others showed that Osr
mutants, such as osm-7 and osm-8, constitutively activate an
osmosensitive gene expression program and have high levels of
the organic osmolyte glycerol (17, 28, 35). However, these
mutants do not exhibit transcriptional patterns characteristic of
the response to other stressors such as heat shock or oxidative
stress (17), and in the case of the osm-8 mutant are resistant to
lethal levels of hyperosmotic stress but not heat shock or oxidative
stress (34). We crossed the Osr mutants osm-7(n1515) and
osm-8(n1518) into the vha-6p::Q44-YFP background and found
that osmotically induced aggregation was strongly attenuated
(Fig. 5 C and D). The protective effect of the Osr mutants is not
limited to the intestine, because the Osr mutants also protect
muscle cells against osmotically induced aggregation (Fig. S7).
We also found that the Osr mutants osm-7 and osm-8 provided
significant protection against aging-induced polyQ aggregation in
the intestine, although such protection was significantly weaker
than that provided by daf-2(e1370), which does not contain elevated
levels of glycerol (33) (Fig. S6). Together, these data show
that genetic and physiological activation of the osmotic stressresponse
pathway, but not the IGF-signaling pathway, attenuates
stress-induced polyQ aggregation in multiple tissues. Furthermore,
the Osr pathway provides weak but significant protection
against aging-induced polyQ aggregation.
Like Growth Factor Signaling, Confers Specific Protection Against
Stress-Induced Aggregation. Reduced signaling of the insulin/insulin-
like growth factor (IGF) pathway protects C. elegans from
several environmental stressors, including hyperosmotic stress
(25, 27, 33). Protection against hyperosmotic stress depends on
the activity of several protein chaperones that are up-regulated
by the FOXO transcription factor daf-16 (33). Such protection
could occur either by preventing the formation of osmotically
induced protein aggregates or by mitigating the physiological
effects of such aggregates. To distinguish between these possibilities,
we crossed the daf-2(e1370) mutant, which causes constitutive
FOXO signaling and protects against hyperosmotic
stress, into the threshold-length polyQ lines. We confirmed that
in these polyQ backgrounds, daf-2(e1370) still activates DAF-16/
FOXO signaling (i.e., formation of dauer larvae at the restrictive
temperature) and provides protection against hyperosmotic
stress [increased 24-h survival on 500 mM NaCl (33)]. The daf-2
(e1370) mutation had no effect on osmotically induced polyQ
aggregate formation in muscle (Fig. S7), and caused only
a modest delay in the kinetics of osmotically induced aggregate
formation in the intestine (Fig. 5 A and B). By contrast, daf-2
mutants exhibit a substantial reduction in the formation of
intestinal age-induced polyQ aggregates (Fig. S6). Therefore,
a reduction in IGF signaling strongly attenuates the formation
of aging-induced Q44-YFP aggregates but has substantially
weaker effects on the formation of osmotically induced
Q44-YFP aggregates.
Another signaling pathway that protects C. elegans from
hyperosmotic stress is the osmotic stress resistance (Osr) pathway
(17, 34–36). Previously, we and others showed that Osr
mutants, such as osm-7 and osm-8, constitutively activate an
osmosensitive gene expression program and have high levels of
the organic osmolyte glycerol (17, 28, 35). However, these
mutants do not exhibit transcriptional patterns characteristic of
the response to other stressors such as heat shock or oxidative
stress (17), and in the case of the osm-8 mutant are resistant to
lethal levels of hyperosmotic stress but not heat shock or oxidative
stress (34). We crossed the Osr mutants osm-7(n1515) and
osm-8(n1518) into the vha-6p::Q44-YFP background and found
that osmotically induced aggregation was strongly attenuated
(Fig. 5 C and D). The protective effect of the Osr mutants is not
limited to the intestine, because the Osr mutants also protect
muscle cells against osmotically induced aggregation (Fig. S7).
We also found that the Osr mutants osm-7 and osm-8 provided
significant protection against aging-induced polyQ aggregation in
the intestine, although such protection was significantly weaker
than that provided by daf-2(e1370), which does not contain elevated
levels of glycerol (33) (Fig. S6). Together, these data show
that genetic and physiological activation of the osmotic stressresponse
pathway, but not the IGF-signaling pathway, attenuates
stress-induced polyQ aggregation in multiple tissues. Furthermore,
the Osr pathway provides weak but significant protection
against aging-induced polyQ aggregation.