CLSTN3B enhances adipocyte lipid droplet structure and function via endoplasmic reticulum contact.

Interorganelle contacts facilitate material exchanges and sustain the structural and functional integrity of organelles. Lipid droplets (LDs) of adipocytes are responsible for energy storage and mobilization responding to body needs. LD biogenesis defects compromise the lipid-storing capacity of adipocytes, resulting in ectopic lipid deposition and metabolic disorders, yet how the uniquely large LDs in adipocytes attain structural and functional maturation is incompletely understood. Here we show that the mammalian adipocyte-specific protein CLSTN3B is crucial for adipocyte LD maturation. CLSTN3B employs an arginine-rich segment to promote extensive contact and hemifusion-like structure formation between the endoplasmic reticulum (ER) and LD, allowing ER-to-LD phospholipid diffusion during LD expansion. CLSTN3B ablation results in reduced LD surface phospholipid density, increased turnover of LD-surface proteins, and impaired LD functions. Our results establish the central role of CLSTN3B in the adipocyte-specific LD maturation pathway that enhances lipid storage and maintenance of metabolic health under caloric overload.

MACC1 as a Potential Target for the Treatment and Prevention of Breast Cancer.

Metastasis associated in colon cancer 1 (MACC1) is an oncogene first identified in colon cancer. MACC1 has been identified in more than 20 different types of solid cancers. It is a key prognostic biomarker in clinical practice and is involved in recurrence, metastasis, and survival in many types of human cancers. MACC1 is significantly associated with the primary tumor, lymph node metastasis, distant metastasis classification, and clinical staging in patients with breast cancer (BC), and MACC1 overexpression is associated with reduced recurrence-free survival (RFS) and worse overall survival (OS) in patients. In addition, MACC1 is involved in BC progression in multiple ways. MACC1 promotes the immune escape of BC cells by affecting the infiltration of immune cells in the tumor microenvironment. Since the FGD5AS1/miR-497/MACC1 axis inhibits the apoptotic pathway in radiation-resistant BC tissues and cell lines, the MACC1 gene may play an important role in BC resistance to radiation. Since MACC1 is involved in numerous biological processes inside and outside BC cells, it is a key player in the tumor microenvironment. Focusing on MACC1, this article briefly discusses its biological effects, emphasizes its molecular mechanisms and pathways of action, and describes its use in the treatment and prevention of breast cancer.

Assembly and function of branched ubiquitin chains.

Post-translational modification with ubiquitin is required for cell division, differentiation, and survival in all eukaryotes. As part of an intricate signaling code, ubiquitin is attached to its targets as single molecules or polymeric chains, with the distinct modifications encoding a wide range of outcomes. After early work focused on homotypic ubiquitin chains, such as the K48-linked polymers that drive proteasomal degradation, recent studies noted abundant conjugates that contained ubiquitin molecules modified on two or more sites. Such branched ubiquitin chains are produced in response to specific signals and they exert functions that are critical for cellular and organismal homeostasis. In this review, we will discuss our rapidly evolving understanding of the assembly and function of branched ubiquitin chains.

Targeting Peripheral Somatosensory Neurons to Improve Tactile-Related Phenotypes in ASD Models.

Somatosensory over-reactivity is common among patients with autism spectrum disorders (ASDs) and is hypothesized to contribute to core ASD behaviors. However, effective treatments for sensory over-reactivity and ASDs are lacking. We found distinct somatosensory neuron pathophysiological mechanisms underlie tactile abnormalities in different ASD mouse models and contribute to some ASD-related behaviors. Developmental loss of ASD-associated genes Shank3 or Mecp2 in peripheral mechanosensory neurons leads to region-specific brain abnormalities, revealing links between developmental somatosensory over-reactivity and the genesis of aberrant behaviors. Moreover, acute treatment with a peripherally restricted GABAA receptor agonist that acts directly on mechanosensory neurons reduced tactile over-reactivity in six distinct ASD models. Chronic treatment of Mecp2 and Shank3 mutant mice improved body condition, some brain abnormalities, anxiety-like behaviors, and some social impairments but not memory impairments, motor deficits, or overgrooming. Our findings reveal a potential therapeutic strategy targeting peripheral mechanosensory neurons to treat tactile over-reactivity and select ASD-related behaviors.

Innervation of thermogenic adipose tissue via a calsyntenin 3ß-S100b axis.

The sympathetic nervous system drives brown and beige adipocyte thermogenesis through the release of noradrenaline from local axons. However, the molecular basis of higher levels of sympathetic innervation of thermogenic fat, compared to white fat, has remained unknown. Here we show that thermogenic adipocytes express a previously unknown, mammal-specific protein of the endoplasmic reticulum that we term calsyntenin 3ß. Genetic loss or gain of expression of calsyntenin 3ß in adipocytes reduces or enhances functional sympathetic innervation, respectively, in adipose tissue. Ablation of calsyntenin 3ß predisposes mice on a high-fat diet to obesity. Mechanistically, calsyntenin 3ß promotes endoplasmic-reticulum localization and secretion of S100b-a protein that lacks a signal peptide-from brown adipocytes. S100b stimulates neurite outgrowth from sympathetic neurons in vitro. A deficiency of S100b phenocopies deficiency of calsyntenin 3ß, and forced expression of S100b in brown adipocytes rescues the defective sympathetic innervation that is caused by ablation of calsyntenin 3ß. Our data reveal a mammal-specific mechanism of communication between thermogenic adipocytes and sympathetic neurons.

Publisher Correction: Innervation of thermogenic adipose tissue via a calsyntenin 3ß-S100b axis.

In Fig. 6a of this Article, the two dots corresponding to Cidea and S100b were erroneously moved to the top left of the volcano plot; this figure has been corrected online.An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Multivesicular bodies mediate long-range retrograde NGF-TrkA signaling.

The development of neurons in the peripheral nervous system is dependent on target-derived, long-range retrograde neurotrophic factor signals. The prevailing view is that target-derived nerve growth factor (NGF), the prototypical neurotrophin, and its receptor TrkA are carried retrogradely by early endosomes, which serve as TrkA signaling platforms in cell bodies. Here, we report that the majority of retrograde TrkA signaling endosomes in mouse sympathetic neurons are ultrastructurally and molecularly defined multivesicular bodies (MVBs). In contrast to MVBs that carry non-TrkA cargoes from distal axons to cell bodies, retrogradely transported TrkA+ MVBs that arrive in cell bodies evade lysosomal fusion and instead evolve into TrkA+ single-membrane vesicles that are signaling competent. Moreover, TrkA kinase activity associated with retrogradely transported TrkA+ MVBs determines TrkA+ endosome evolution and fate. Thus, MVBs deliver long-range retrograde NGF signals and serve as signaling and sorting platforms in the cell soma, and MVB cargoes dictate their vesicular fate.