Heterotypic Signals from Neural HSF-1 Separate Thermotolerance from Longevity

Abstract

Integrating stress responses across tissues is essential for the survival of multicellular organisms. The metazoan nervous system can sense protein-misfolding stress arising in different subcellular compartments and initiate cytoprotective transcriptional responses in the periphery. Several subcellular compartments possess a homotypic signal whereby the respective compartment relies on a single signaling mechanism to convey information within the affected cell to the same stress-responsive pathway in peripheral tissues. In contrast, we find that the heat shock transcription factor, HSF-1, specifies its mode of transcellular protection via two distinct signaling pathways. Upon thermal stress, neural HSF-1 primes peripheral tissues through the thermosensory neural circuit to mount a heat shock response. Independent of this thermosensory circuit, neural HSF-1 activates the FOXO transcription factor, DAF-16, in the periphery and prolongs lifespan. Thus a single transcription factor can coordinate different stress response pathways to specify its mode of protection against changing environmental conditions.

Figure 1. Neural overexpression of hsf-1 protects C. elegans against heat stress and aging

(A) Transcript abundance of hsf-1 determined by quantitative RT-PCR analysis of wild type (N2) and rab-3p::hsf-1 transgenic animals (AGD1289). (B) Thermotolerance of wild type and rab-3p::hsf-1 transgenic worms shifted from permissive (20°) to heat shock (34°) temperatures for 14 hours. (C) Lifespan survival curves of wild type and rab-3p::hsf-1 transgenic strains at permissive temperatures (20°). Lifespan statistics are found in Table 1.

Figure 2. Neural hsf-1 overexpression enhances heat inducible chaperone expression in all tissues and requires an intact thermosensory circuit for heat protection but not lifespan extension

(A) Fluorescent microscopy of C. elegans expressing GFP from the hsp-16.2 promoter in control (CL2070) and rab-3p::hsf-1 transgenic animals (AGD1448), at permissive (20°C) and heat shock (34°C) temperatures. (B) Large-particle flow cytometry was used to quantify GFP fluorescence from strains used in (A). (C) Transcript levels of endogenous hsp-16.2 determined by quantitative RT-PCR from day 1 adult wild type and rab-3p::hsf-1 transgenic animals (AGD1289). (D) Western blot analysis of endogenous HSP-16 from strains used in (C). (E) Thermotolerance of WT, ttx-3(ks5), rab-3p::hsf-1 (AGD1289), and rab-3p::hsf-1;ttx-3(ks5) (AGD1449) animals was assessed at 34°C. (F) Lifespan survival was performed at 20°C on strains used in (E). Lifespan statistics are found in Table 1.

Figure 3. daf-16 is required for neural hsf-1 to induce sod-3 expression in peripheral tissues and extend lifespan, but is dispensable for increased thermotolerance

(A) Fluorescent microscopy of C. elegans expressing GFP from the sod-3 promoter in control (CF1553), rab-3p::hsf-1 (AGD1198) and rab-3p::hsf-1; daf-16(mu86) (AGD1457) animals at 20°C. (B) Quantification of GFP fluorescence from strains used in (A) as determined by large-particle flow cytometry. (C) Transcript levels of endogenous sod-3 determined by quantitative RT-PCR from day 1 adult WT, daf-16(mu86), rab-3p::hsf-1 (AGD1289) and rab-3p::hsf-1; daf-16(mu86) (AGD1217) animals. (D) Lifespan survival was assessed at 20°C for strains used in (C). Lifespan statistics are found in Table 1. (E) Thermotolerance was determined at 34°C for strains used in (C-D).

Figure 4. Neural overexpression of hsf-1 requires daf-16 in the intestine to activate sod-3 and extend lifespan

(A-C) Lifespan survival curves and representative sod-3p::GFP fluorescent micrographs of rab-3p::hsf-1 transgenic animals with different tissue-specific daf-16 rescues in an otherwise daf-16(mu86) mutant background. Expression of daf-16 is ectopically restored in individual tissues of daf-16(mu86) null animals including the (A) nervous system (AGD1273), (B) intestine (AGD1277), and (C) body-wall muscle (AGD1279). Lifespan statistics are found in Table 1.

Figure 5. hsf-1 is required in peripheral tissues for neural hsf-1 overexpressing worms to extend lifespan

(A) Lifespan survival curves of WT and rab-3p::hsf-1 overexpressing nematodes (AGD1289) in the presence or absence of the hypomorphic hsf-1(sy441) mutation (AGD1471). Lifespan statistics are found in Table 1. (B) Model depicting how heterotypic signals by neural hsf-1 separate thermal protection from age regulation. Under thermal stress, HSF-1 in the nervous system signals to peripheral tissues through the thermosensory neural circuit and enhances the heat shock response to protect worms (left model). Conversely, neural hsf-1 functions independently of the thermosensory circuit to generate a transcellular signal which activates DAF-16 and HSF-1 in the intestine and drives pro-longevity gene expression (right model).