GRD-1/PTR-11, the C. elegans hedgehog/patched-like morphogen-receptor pair, modulates developmental rate

Non-cell-autonomous regulation of mTORC2 by Hedgehog signaling maintains lipid homeostasis

Organisms allocate energetic resources between essential cellular processes to maintain homeostasis and, in turn, maximize fitness. The nutritional regulators of energy homeostasis have been studied in detail; however, how developmental signals might impinge on these pathways to govern metabolism is poorly understood. Here, we identify a non-canonical role for Hedgehog (Hh), a classic regulator of development, in maintaining intestinal lipid homeostasis in Caenorhabditis elegans. We demonstrate, using C. elegans and mouse hepatocytes, that Hh metabolic regulation does not occur through the canonical Hh transcription factor TRA-1/GLI, but rather via non-canonical signaling that engages mammalian target of rapamycin complex 2 (mTORC2). Hh mutants display impaired lipid homeostasis, decreased growth, and upregulation of autophagy factors, mimicking loss of mTORC2. Additionally, we find that Hh inhibits p38 MAPK signaling in parallel to mTORC2 activation to modulate lipid homeostasis. Our findings reveal a non-canonical role for Hh signaling in lipid metabolism via regulation of core homeostatic pathways.

The Caenorhabditis elegans Dispatched ortholog, CHE-14, is dispensable for apical secretion of the Hedgehog-related proteins GRL-2 and WRT-10

C. elegans nematodes possess expanded families of Hedgehog related (Hh-r) and Patched/Dispatched-related (PTR) proteins but their functional relationship remains unclear. Here we investigated whether CHE-14 , the closest C. elegans ortholog for the Hedgehog transporter Dispatched, was necessary for the secretion of two tagged Hh-r proteins: WRT-10 and GRL-2 . We report that CHE-14 is dispensable for the apical localization of GRL-2 and WRT-10 . We also show that animals lacking CHE-14 and another redundant PTR protein DAF-6 also secrete WRT-10 , suggesting neither are required for secretion of these specific Hh-r proteins.

Caenorhabditis elegans Hedgehog-related proteins are tissue- and substructure-specific components of the cuticle and precuticle

In Caenorhabditis elegans, expanded families of divergent Hedgehog-related and patched-related proteins promote numerous processes ranging from epithelial and sense organ development to pathogen responses to cuticle shedding during the molt cycle. The molecular functions of these proteins have been mysterious since nematodes lack a canonical Hedgehog signaling pathway. Here we show that Hedgehog-related proteins are components of the cuticle and precuticle apical extracellular matrices that coat, shape, and protect external epithelia. Of four Hedgehog-related proteins imaged, two (GRL-2 and GRL-18) stably associated with the cuticles of specific tubes and two (GRL-7 and WRT-10) labeled precuticle substructures such as furrows or alae. We found that wrt-10 mutations disrupt cuticle alae ridges, consistent with a structural role in matrix organization. We hypothesize that most nematode Hedgehog-related proteins are apical extracellular matrix components, a model that could explain many of the reported functions for this family. These results highlight ancient connections between Hedgehog proteins and the extracellular matrix and suggest that any signaling roles of C. elegans Hedgehog-related proteins will be intimately related to their matrix association.

The Caenorhabditis elegans cuticle and precuticle: a model for studying dynamic apical extracellular matrices in vivo

Apical extracellular matrices (aECMs) coat the exposed surfaces of animal bodies to shape tissues, influence social interactions, and protect against pathogens and other environmental challenges. In the nematode Caenorhabditis elegans, collagenous cuticle and zona pellucida protein-rich precuticle aECMs alternately coat external epithelia across the molt cycle and play many important roles in the worm's development, behavior, and physiology. Both these types of aECMs contain many matrix proteins related to those in vertebrates, as well as some that are nematode-specific. Extensive differences observed among tissues and life stages demonstrate that aECMs are a major feature of epithelial cell identity. In addition to forming discrete layers, some cuticle components assemble into complex substructures such as ridges, furrows, and nanoscale pillars. The epidermis and cuticle are mechanically linked, allowing the epidermis to sense cuticle damage and induce protective innate immune and stress responses. The C. elegans model, with its optical transparency, facilitates the study of aECM cell biology and structure/function relationships and all the myriad ways by which aECM can influence an organism.

Non-cell-autonomous regulation of mTORC2 by Hedgehog signaling maintains lipid homeostasis

Organisms must appropriately allocate energetic resources between essential cellular processes to maintain homeostasis and in turn, maximize fitness. The nutritional and homeostatic regulators of energy homeostasis have been studied in detail; however, how developmental signals might impinge on these pathways to govern cellular metabolism is poorly understood. Here, we identify a non-canonical role for Hedgehog (Hh), a classic regulator of development, in maintaining intestinal lipid homeostasis in C. elegans . We find that expression of two Hh ligands, GRD-3 and GRD-4, is controlled by the LIN-29/EGR transcription factor in the hypodermis, where the Hh secretion factor CHE-14/Dispatched also facilitates non-cell autonomous Hh signaling. We demonstrate, using C. elegans and mouse hepatocytes, that Hh metabolic regulation does not occur through the canonical Hh transcription factor, TRA-1/GLI, but rather through non-canonical signaling that engages mTOR Complex 2 (mTORC2) in the intestine. Hh mutants display impaired lipid homeostasis, including reduced lipoprotein synthesis and fat accumulation, decreased growth, and upregulation of autophagy factors, mimicking loss of mTORC2. Additionally, we found that Hh inhibits p38 MAPK signaling in parallel to mTORC2 activation and that both pathways act together to modulate of lipid homeostasis. Our findings show a non-canonical role for Hedgehog signaling in lipid metabolism via regulation of core homeostatic pathways and reveal a new mechanism by which developmental timing events govern metabolic decisions.

C. elegans Hedgehog-related proteins are tissue- and substructure-specific components of the cuticle and pre-cuticle

In C. elegans, divergent Hedgehog-related (Hh-r) and Patched-related (PTR) proteins promote numerous processes ranging from epithelial and sense organ development to pathogen responses to cuticle shedding during the molt cycle. Here we show that Hh-r proteins are actual components of the cuticle and pre-cuticle apical extracellular matrices (aECMs) that coat, shape, and protect external epithelia. Different Hh-r proteins stably associate with the aECMs of specific tissues and with specific substructures such as furrows and alae. Hh-r mutations can disrupt matrix structure. These results provide a unifying model for the function of nematode Hh-r proteins and highlight ancient connections between Hh proteins and the extracellular matrix.