Autophagy-Associated Shrinkage of the Hepatopancreas in Fasting Male Macrobrachium rosenbergii Is Rescued by Neuropeptide F

Differential expression of neuropeptide F in the digestive organs of female freshwater prawn, Macrobrachium rosenbergii, during the ovarian cycle

Neuropeptide F is a key hormone that controls feeding in invertebrates, including decapod crustaceans. We investigated the differential expression of Macrobrachium rosenbergii neuropeptide F (MrNPF) in the digestive organs of female prawns, M. rosenbergii, during the ovarian cycle. By using RT-qPCR, the expression of MrNPF mRNA in the esophagus (ESO), cardia (CD), and pylorus (PY) of the foregut (FG) gradually increased from stage II and peaked at stage III. In the midgut (MG), hindgut (HG), and hepatopancreas (HP), MrNPF mRNA increased from stage I, reaching a maximal level at stage II, and declined by about half at stages III and IV (P < 0.05). In the ESO, CD, and PY, strong MrNPF-immunoreactivities were seen in the epithelium, muscle, and lamina propria. Intense MrNPF-ir was found in the MG cells and the muscular layer. In the HG, MrNPF-ir was detected in the epithelium of the villi and gland regions, while MrNPF-ir was also more intense in the F-, R-, and B-cells in the HP. However, we found little colocalization between the MrNPF and PGP9.5/ChAT in digestive tissues, implying that most of the positive cells might not be neurons but could be digestive tract-associated endocrine cells that produce and secrete MrNPF to control digestive organ functions in feeding and utilizing feed. Taken together, our first findings indicated that MrNPF was differentially expressed in digestive organs in correlation with the ovarian cycle, suggesting an important link between MrNPF, the physiology of various digestive organs in feeding, and possibly ovarian maturation in female M. rosenbergii.

Temporal and Spatial Signatures of Scylla paramamosain Transcriptome Reveal Mechanistic Insights into Endogenous Ovarian Maturation under Risk of Starvation

Variability in food availability leads to condition-dependent investments in reproduction. This study is aimed at understanding the metabolic response and regulatory mechanism of female Scylla paramamosain in response to starvation in a temporal- and tissue-specific manner. The mud crabs were starved for 7 (control), 14, 28, and 40 days for histological and biochemical analysis in the hepatopancreas, ovary, and serum, as well as for RNA sequencing on the hepatopancreas and ovary. We further highlighted candidate gene modules highly linked to physiological traits. Collectively, our observations suggested that starvation triggered endogenous ovarian maturation at the expense of hepatopancreas mass, with both metabolic adjustments to optimize energy and fatty acid supply from hepatopancreas to ovary in the early phase, followed by the activation of autophagy-related pathways in both organs over prolonged starvation. These specific adaptive responses might be considered efficient strategies to stimulate ovarian maturation of Scylla paramamosain under fasting stress, which improves the nutritional value of female mud crabs and other economically important crustaceans.

MYC drives autophagy to adapt to stress in Penaeus vannamei

MYC proto-oncogene (MYC), a first oncogenic nuclear transcription factor isolated from the human genome, belongs to the helix loop helix/leucine zipper protein family (bHLHzip). MYC plays an important part in the process of various physiological and biochemical of vertebrate, such as cell growth, proliferation, cycle, and autophagy. However, its molecular regulation mechanism and function in invertebrates are still unclear. In this study, a novel transcription factor MYC gene was screened, cloned, and characterized from Penaeus vannamei. The open reading frame of PvMYC was 1593bp, encode a polypeptide of 530 amino acids with molecular weight of 58.5 kDa, and a theoretical PI of 5.75. The results of tissue distribution showed that PvMYC was constitutively expressed in all detected tissues, and highest expression in hepatopancreas. The expression level of PvMYC up-regulated significantly and responded to low temperature stress by nuclear ectopic after low temperature stress. Overexpression of PvMYC in shrimp hemocytes negatively regulated the expression of Beclin-1 and reduced the conversion from LC3I to LC3II, yet p62 was decreased significantly. Meanwhile, RAPA eliminated the inhibition of autophagy caused by overexpression of PvMYC. ROS levels and autophagy flux showed the similar trend under low temperature stress after silencing PvMYC. The expression levels of Beclin-1, key ATG gene and LC3II increased significantly, while p62 decreased significantly under the same conditions. In addition, the Total hemocyte count (THC) decreased sharply, and accelerated the injury of hepatopancreas under low temperature stress after silencing PvMYC. Collectively, these results suggest that PvMYC has vital role in the cold adaptation mechanism of P. vannamei by negatively regulating autophagy.

Targeting lipophagy as a potential therapeutic strategy for nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) is becoming an increasingly serious disease worldwide. Unfortunately, no specific drug has been approved to treat NAFLD. Accumulating evidence suggests that lipotoxicity, which is induced by an excess of intracellular triacylglycerols (TAGs), is a potential mechanism underlying the ill-defined progression of NAFLD. Under physiological conditions, a balance is maintained between TAGs and free fatty acids (FFAs) in the liver. TAGs are catabolized to FFAs through neutral lipolysis and/or lipophagy, while FFAs can be anabolized to TAGs through an esterification reaction. However, in the livers of patients with NAFLD, lipophagy appears to fail. Reversing this abnormal state through several lipophagic molecules (mTORC1, AMPK, PLIN, etc.) facilitates NAFLD amelioration; therefore, restoring failed lipophagy may be a highly efficient therapeutic strategy for NAFLD. Here, we outline the lipophagy phases with the relevant important proteins and discuss the roles of lipophagy in the progression of NAFLD. Additionally, the potential candidate drugs with therapeutic value targeting these proteins are discussed to show novel strategies for future treatment of NAFLD.

Antistarvation Strategies of E. Sinensis: Regulatory Networks under Hepatopancreas Consumption

Crustaceans have a more persistent starvation tolerance than mammals, birds, reptiles, and even fish. This study is aimed at assessing the survival strategy and regulatory mechanism of crustaceans in response to starvation through an animal model using Eriocheir sinensis. In the 42-day starvation experiment, the hepatopancreas was found to become the target organ, which was characterized by atrophy of the thin wall in the hepatic tubules and expansion of the lumen. During short-term starvation, E. sinensis activates lipid and glycogen metabolism in the hepatopancreas with lipid metabolism dominating. In lipid metabolism, there was a significant decline in triglyceride, whereas cholesterol did not change significantly. Meanwhile, the fatty acid metabolism pathway was inhibited, but autophagy increased in the hepatopancreas, which may be the selective pathway for the decomposition of intracellular substances. However, under long-term starvation, the stored energy in the hepatopancreas was depleted, and E. sinensis selects to consume hepatopancreatic cells and maintain energy metabolism through apoptosis, which was triggered by both the death receptor pathway and the mitochondrial pathway. In addition, cell proliferation was blocked to reduce unnecessary energy consumption.

Cell proliferation controls body size growth, tentacle morphogenesis, and regeneration in hydrozoan jellyfish Cladonema pacificum

Jellyfish have existed on the earth for around 600 million years and have evolved in response to environmental changes. Hydrozoan jellyfish, members of phylum Cnidaria, exist in multiple life stages, including planula larvae, vegetatively-propagating polyps, and sexually-reproducing medusae. Although free-swimming medusae display complex morphology and exhibit increase in body size and regenerative ability, their underlying cellular mechanisms are poorly understood. Here, we investigate the roles of cell proliferation in body-size growth, appendage morphogenesis, and regeneration using Cladonema pacificum as a hydrozoan jellyfish model. By examining the distribution of S phase cells and mitotic cells, we revealed spatially distinct proliferating cell populations in medusae, uniform cell proliferation in the umbrella, and clustered cell proliferation in tentacles. Blocking cell proliferation by hydroxyurea caused inhibition of body size growth and defects in tentacle branching, nematocyte differentiation, and regeneration. Local cell proliferation in tentacle bulbs is observed in medusae of two other hydrozoan species, Cytaeis uchidae and Rathkea octopunctata, indicating that it may be a conserved feature among hydrozoan jellyfish. Altogether, our results suggest that hydrozoan medusae possess actively proliferating cells and provide experimental evidence regarding the role of cell proliferation in body-size control, tentacle morphogenesis, and regeneration.

Distribution of neuropeptide F in the ventral nerve cord and its possible role on testicular development and germ cell proliferation in the giant freshwater prawn, Macrobrachium rosenbergii

Neuropeptide F in invertebrates is a homolog of neuropeptide Y in mammals and it is a member of FMRFamide-related peptides. In arthropods, such as insects, there are two types of neuropeptide F comprising long neuropeptide F (NPF) and short neuropeptide F (sNPF). Both NPFs are known to play a crucial role in the regulations of foraging, feeding-related behaviors, circadian rhythm, stress responses, aggression and reproduction in invertebrates. We have earlier found that in the giant freshwater prawn, Macrobrachium rosenbergii, there are three isoforms of NPF and four isoforms of sNPF and that NPFs are expressed in the eyestalks and brain. In the present study, we investigate further the tissue distribution of NPF-I in the ventral nerve cord (VNC) and its role in the development of testes in small male (SM) Macrobrachium rosenbergii. By immunolocalization, using the rabbit polyclonal antibody against NPF-I as a probe, we could detect NPF-I immunoreactivity in the neuropils and neuronal clusters of the subesophageal ganglia (SEG), thoracic ganglia (TG) and abdominal ganglia (AG) of the SM prawns. In functional assays, the administrations of synthetic NPF-I (KPDPTQLAAMADALKYLQELDKYYSQVSRPRFamide) and sNPF (APALRLRFamide) peptides significantly increased the growth rates of SM prawns and significantly increased the gonadosomatic index (GSI) and proliferations of early germ cells in the seminiferous tubules of their testes. It is, therefore, suggestive that NPFs may play critical roles in energy homeostasis towards promoting growth as well as testicular development in prawns that could be applied in the aquaculture of this species.