Vertebrate extracellular matrix protein hemicentin-1 interacts physically and genetically with basement membrane protein nidogen-2

Matricellular proteins in immunometabolism and tissue homeostasis

Matricellular proteins are integral non-structural components of the extracellular matrix. They serve as essential modulators of immunometabolism and tissue homeostasis, playing critical roles in physiological and pathological conditions. These extracellular matrix proteins including thrombospondins, osteopontin, tenascins, the secreted protein acidic and rich in cysteine (SPARC) family, the Cyr61, CTGF, NOV (CCN) family, and fibulins have multi-faceted functions in regulating immune cell functions, metabolic pathways, and tissue homeostasis. They are involved in immune-metabolic regulation and influence processes such as insulin signaling, adipogenesis, lipid metabolism, and immune cell function, playing significant roles in metabolic disorders such as obesity and diabetes. Furthermore, their modulation of tissue homeostasis processes including cellular adhesion, differentiation, migration, repair, and regeneration is instrumental for maintaining tissue integrity and function. The importance of these proteins in maintaining physiological equilibrium is underscored by the fact that alterations in their expression or function often coincide with disease manifestation. This review contributes to our growing understanding of these proteins, their mechanisms, and their potential therapeutic applications. [BMB Reports 2024; 57(9): 400-416].

Insulin-Independent Regulation of Type 1 Diabetes via Brown Adipocyte-Secreted Proteins and the Novel Glucagon Regulator Nidogen-2

Current treatments for type 1 diabetes (T1D) focus on insulin replacement. We demonstrate the therapeutic potential of a secreted protein fraction from embryonic brown adipose tissue (BAT), independent of insulin. The large molecular weight secreted fraction mediates insulin receptor-dependent recovery of euglycemia in a T1D animal model, nonobese diabetic (NOD) mice, by suppressing glucagon secretion. This fraction also promotes white adipocyte differentiation and browning, maintains healthy BAT, and enhances glucose uptake in adipose tissue, skeletal muscle, and liver. From this fraction, we identify nidogen-2 as a critical BAT-secreted protein that reverses hyperglycemia in NOD mice, inhibits glucagon secretion from pancreatic α-cells, and mimics other actions of the entire secreted fraction. These findings confirm that BAT transplants affect physiology and demonstrate that BAT-secreted peptides represent a novel therapeutic approach to diabetes management. Furthermore, our research reveals a novel signaling role for nidogen-2, beyond its traditional classification as an extracellular matrix protein.

HIGHLIGHTS

The large molecular weight brown adipocyte-secreted protein fraction suppresses glucagon secretion and normalizes glycemia in mouse models of type 1 diabetes (T1D), independent of insulin, offering a novel therapeutic strategy for disease management.Nidogen-2, a critical component of this fraction, is identified as an inhibitor of glucagon secretion in pancreatic α-cells by regulating intracellular messenger activities.The large-secreted protein fraction prevents T1D-related whitening of brown adipose tissue, promotes adipocyte differentiation, and enhances browning of inguinal white adipose tissue.This fraction enhances glucose uptake in adipose tissue, skeletal muscle, and liver through an insulin receptor-dependent pathway.

Lens placode modulates extracellular matrix formation during early eye development

The role extracellular matrix (ECM) in multiple events of morphogenesis has been well described, little is known about its specific role in early eye development. One of the first morphogenic events in lens development is placodal thickening, which converts the presumptive lens ectoderm from cuboidal to pseudostratified epithelium. This process occurs in the anterior pre-placodal ectoderm when the optic vesicle approaches the cephalic ectoderm and is regulated by transcription factor Pax6 and secreted BMP4. Since cells and ECM have a dynamic relationship of interdependence and modulation, we hypothesized that the ECM evolves with cell shape changes during lens placode formation. This study investigates changes in optic ECM including both protein distribution deposition, extracellular gelatinase activity and gene expression patterns during early optic development using chicken and mouse models. In particular, the expression of Timp2, a metalloprotease inhibitor, corresponds with a decrease in gelatinase activity within the optic ECM. Furthermore, we demonstrate that optic ECM remodeling depends on BMP signaling in the placode. Together, our findings suggest that the lens placode plays an active role in remodeling the optic ECM during early eye development.

wnt10a is required for zebrafish median fin fold maintenance and adult unpaired fin metamorphosis

BACKGROUND

Mutations of human WNT10A are associated with odonto-ectodermal dysplasia syndromes. Here, we present analyses of wnt10a loss-of-function mutants in the zebrafish.

RESULTS

wnt10a mutant zebrafish embryos display impaired tooth development and a collapsing median fin fold (MFF). Rescue experiments show that wnt10a is essential for MFF maintenance both during embryogenesis and later metamorphosis. The MFF collapse could not be attributed to increased cell death or altered proliferation rates of MFF cell types. Rather, wnt10a mutants show reduced expression levels of dlx2a in distal-most MFF cells, followed by compromised expression of col1a1a and other extracellular matrix proteins encoding genes. Transmission electron microscopy analysis shows that although dermal MFF compartments of wnt10a mutants initially are of normal morphology, with regular collagenous actinotrichia, positioning of actinotrichia within the cleft of distal MFF cells becomes compromised, coinciding with actinotrichia shrinkage and MFF collapse.

CONCLUSIONS

MFF collapse of wnt10a mutant zebrafish is likely caused by the loss of distal properties in the developing MFF, strikingly similar to the proposed molecular pathomechanisms underlying the teeth defects caused by the loss of Wnt10 in fish and mammals. In addition, it points to thus fur unknown mechanisms controlling the linear growth and stability of actinotrichia and their collagen fibrils.

Lens Placode Modulates Extracellular Matrix Formation During Early Eye Development

The role extracellular matrix (ECM) in multiple events of morphogenesis has been well described, little is known about its specific role in early eye development. One of the first morphogenic events in lens development is placodal thickening, which converts the presumptive lens ectoderm from cuboidal to pseudostratified epithelium. This process occurs in the anterior pre-placodal ectoderm when the optic vesicle approaches the cephalic ectoderm. Since cells and ECM have a dynamic relationship of interdependence and modulation, we hypothesized that the ECM evolves with cell shape changes during lens placode formation. This study investigates changes in optic ECM including both protein distribution deposition, extracellular gelatinase activity and gene expression patterns during early optic development using chicken and mouse models. In particular, the expression of Timp2 , a metalloprotease inhibitor, corresponds with a decrease in gelatinase activity within the optic ECM. Furthermore, we demonstrate that optic ECM remodeling depends on BMP signaling in the placode. Together, our findings suggest that the lens placode plays an active role in remodeling the optic ECM during early eye development.

Genome-wide detection of positive and balancing signatures of selection shared by four domesticated rainbow trout populations (Oncorhynchus mykiss)

BACKGROUND

Evolutionary processes leave footprints along the genome over time. Highly homozygous regions may correspond to positive selection of favorable alleles, while maintenance of heterozygous regions may be due to balancing selection phenomena. We analyzed data from 176 fish from four disconnected domestic rainbow trout populations that were genotyped using a high-density Axiom Trout genotyping 665K single nucleotide polymorphism array, including 20 from the US and 156 from three French lines. Using methods based on runs of homozygosity and extended haplotype homozygosity, we detected signatures of selection in these four populations.

RESULTS

Nine genomic regions that included 253 genes were identified as being under positive selection in all four populations Most were located on chromosome 2 but also on chromosomes 12, 15, 16, and 20. In addition, four heterozygous regions that contain 29 genes that are putatively under balancing selection were also shared by the four populations. These were located on chromosomes 10, 13, and 19. Regardless of the homozygous or heterozygous nature of the regions, in each region, we detected several genes that are highly conserved among vertebrates due to their critical roles in cellular and nuclear organization, embryonic development, or immunity. We identified new candidate genes involved in rainbow trout fitness, as well as 17 genes that were previously identified to be under positive selection, 10 of which in other fishes (auts2, atp1b3, zp4, znf135, igf-1α, brd2, col9a2, mrap2, pbx1, and emilin-3).

CONCLUSIONS

Using material from disconnected populations of different origins allowed us to draw a genome-wide map of signatures of positive selection that are shared between these rainbow trout populations, and to identify several regions that are putatively under balancing selection. These results provide a valuable resource for future investigations of the dynamics of genetic diversity and genome evolution during domestication.

Matricellular Proteins in the Homeostasis, Regeneration, and Aging of Skin

Matricellular proteins are secreted extracellular proteins that bear no primary structural functions but play crucial roles in tissue remodeling during development, homeostasis, and aging. Despite their low expression after birth, matricellular proteins within skin compartments support the structural function of many extracellular matrix proteins, such as collagens. In this review, we summarize the function of matricellular proteins in skin stem cell niches that influence stem cells' fate and self-renewal ability. In the epidermal stem cell niche, fibulin 7 promotes epidermal stem cells' heterogeneity and fitness into old age, and the transforming growth factor-β-induced protein ig-h3 (TGFBI)-enhances epidermal stem cell growth and wound healing. In the hair follicle stem cell niche, matricellular proteins such as periostin, tenascin C, SPARC, fibulin 1, CCN2, and R-Spondin 2 and 3 modulate stem cell activity during the hair cycle and may stabilize arrector pili muscle attachment to the hair follicle during piloerections (goosebumps). In skin wound healing, matricellular proteins are upregulated, and their functions have been examined in various gain-and-loss-of-function studies. However, much remains unknown concerning whether these proteins modulate skin stem cell behavior, plasticity, or cell-cell communications during wound healing and aging, leaving a new avenue for future studies.