Skip to main content

Age-related resistance of skeletal muscle-derived progenitor cells to SPARC may explain a shift from myogenesis to adipogenesis

Age-related resistance of skeletal muscle-derived progenitor cells to SPARC may explain a shift from myogenesis to adipogenesis


Abstract

Aging causes phenotypic changes in skeletal muscle progenitor cells (SMPCs) that lead to the loss of myogenicity and adipogenesis. Secreted protein acidic and rich in cysteine (SPARC), which is secreted from SMPCs, stimulates myogenesis and inhibits adipogenesis. The present study aimed to examine whether changes in SPARC expression, its signaling pathway, or both are involved in age-related phenotypic changes in SMPCs. SPARC expression levels were comparable in SMPCs derived from young and old rats. However, when SPARC expression was reduced by a SPARC-specific siRNA, SMPCs from young rats showed reduced myogenesis and increased adipogenesis. In striking contrast, old rats showed little changes in these functions. Recombinant SPARC was effective in inhibiting adipogenesis and promoting myogenesis of SMPCs from young rats but had no effect on SMPCs from old rats when endogenous SPARC levels were reduced by the SPARC-siRNA. Further, the level of integrin α5, a subunit of the putative SPARC receptor, was decreased in SMPCs from old rats, and its inhibition in SMPCs from young rats by siRNA reduced adipogenesis in response to SPARC. These results suggest that, although SPARC plays a role in regulating SMPC function, SMPCs become refractory to the action of SPARC with age. Our data may explain an age-related shift from myogenesis to adipogenesis, associated with sarcopenia.

Introduction

Aging impairs organ function. Human body mass, of which skeletal muscle is the most abundant tissue, declines with age [1]. The decline in skeletal muscle (sarcopenia) is defined clinically by a loss of lean muscle mass and impairment of its function [2]. Adipose tissue infiltration is often observed in skeletal muscles of the elderly [3], and this intramuscular adipose tissue (IMAT) causes poor physical performance [4] and plays a role in insulin resistance and obesity [5]. Therefore, treating these conditions as well as sarcopenia will depend on a better understanding of the mechanism of IMAT accumulation.

Skeletal muscle contains several types of SMPCs, including satellite cells that possess almost exclusively myogenic potential [6]. Adult mouse SMPCs spontaneously differentiate into adipocytes [7] and their adipogenic potential increases with age [8]. Vettor, et al. postulate that SMPCs form IMAT [9], thus suggesting that alterations in the differentiation of SMPCs cause sarcopenia. Differentiation of SMPCs is greatly affected by their microenvironment [10, 11]. For example, degradation of basal lamina, a major component of the SMPC niche, promotes adipogenic differentiation of SMPCs [11]. Basal lamina contains several extracellular matrix (ECM) proteins such as collagen, laminin, fibronectin and proteoglycans. ECM proteins function as structural supports for SMPCs and bind growth factors that regulate SMPC function [12].

SPARC (also known as osteonectin or BM-40) is a nonstructural, matricellular glycoprotein that is secreted into the niche and functions in cell adhesion, angiogenesis, growth factor binding, and cell differentiation [13, 14]. SPARC inhibits adipogenesis of preadipocytes by enhancing β-catenin signaling [15]. It also promotes myogenic differentiation of C2C12 and MM14 myoblasts [16, 17]. SPARC is expressed by SMPCs [18] and may regulate SMPC function in an autocrine manner. SPARC-null mice exhibit early-onset cataracts [19], osteopenia-like decline of bone formation [20], increased obesity, and decreased skeletal muscle mass [21]. These phenotypes are typically observed in old mice.

In the present study, we examined whether changes in SPARC expression or signaling are involved in age-related phenotypic changes during the differentiation of SMPCs.

Results

SMPCs express SPARC regardless of their differentiation state during myogenesis and adipogenesis

SMPCs express SPARC [18] and can differentiate into myogenic and adipogenic cells [7]. To examine whether the expression of SPARC by SMPCs is differentiation dependent, we immunostained SMPCs derived from young rats by using antibodies specific for MyoD, C/EBPα, myosin heavy chain (MHC), and SPARC (Figure 1). MyoD is a transcription factor that plays a critical role in myogenesis. MyoD-positive cells coexpressed SPARC in SMPC cultures 3 days after plating. MHC-positive myotubes, induced by culturing SMPCs in media containing 2% HS, were also positive for SPARC. Approximately 20% of SMPCs expressed C/EBPα-, a transcription factor involved in adipogenesis, and were stained with Oil Red-O, an indicator of adipogenesis. Both C/EBPα- and Oil Red-O-positive cells expressed SPARC. In all cases, SPARC expression was detected in both non-myogenic and non-adipogenic cells, indicating that SMPC express SPARC regardless of their state of differentiation.

Immunocytochemistry of SPARC in SMPCs

Figure 1. Immunocytochemistry of SPARC in SMPCs. Immunostaining of SPARC during myogenic and adipogenic differentiation of SMPCs from young rats. Cells were co-stained with anti-MyoD and anti-SPARC 3 days after plating or with anti-MHC and anti-SPARC 4 days after exposure to media containing 2% HS. Co-staining with anti-SPARC and anti-C/EBPα or Oil Red O staining was performed 4 days after culturing in the media to induce adipogenic differentiation (ADM). Nuclei were visualized with Hoechst 33258 Dye (blue). White arrowheads indicate double-positive cells (MyoD+/SPARC+, MHC+/SPARC+, C/EBPα+/SPARC+, and Oil Red O+/SPARC+), whereas black arrowheads indicate cells that are only positive for SPARC (MyoD-/SPARC+, MHC-/SPARC+, C/EBPα-/SPARC+, and Oil Red O-/SPARC+). Scale bar = 100 μm.

SPARC expression levels in SMPCs do not change with age

The adipogenic potential of SMPC increases with age [8], which we confirmed here (data not shown). Because SPARC inhibits adipogenesis [15], the age-related increases in the adipogenic potential of SMPCs may be due to a decline in their secretion of SPARC. However, quantitative PCR analysis revealed no differences in SPARC expression levels between SMPCs from young and old rats (Figure 2A). Immunoblotting and immunostaining of SPARC in young and old SMPCs also showed that the levels of SPARC expression in SMPCs does not change with age (Figures 2B and 2C). These results suggest that the increased adipogenic potential of old SMPCs is not caused by a decline in SPARC.



When people speak of contemporary medicine, accuracy plays one of the most crucial roles and human lives are literally dependent on it. Hereby, any researches pertaining to medicine are necessary to comply with the top standards. The issue today is that any conclusions of researches can be shared online and used as a reference without being adequately checked and approved. Mikhail (Misha) Blagosklonny of Oncotarget perfectly understood this challenge and tried to create an alternative solution. That’s how a weekly oncology-focused research journal called “Oncotarget” has been founded back in 2010. The major principle of this journal is related to Altmetric scores that are used as a quality indicator. That assists both readers and authors to verify publications with Altmetric Article Reports that provide “real-time feedback containing data summary related to a particular publication.” Oncotarget website demonstrates a full publications list with corresponding scores above 100 as well as reports discussed above. Mikhail (Misha) Blagosklonny glad to share his new approach and hopes it creates the necessary assistance to anyone, who has interest in oncology.
“A diagnostic autoantibody signature for primary cutaneous melanoma” has the Altmetric score of 594. This article was published back in 2018 by Oncotarget and written by various experts from Hollywood Private Hospital, Edith Cowan University, Dermatology Specialist Group, St. John of God Hospital and The University of Western Australia. The introduction of the study mentions that “recent data shows that Australians are four times more likely to develop a cancer of the skin than any other type of cancer”, and provides an insight on melanoma that “is curable by surgical excision in the majority of cases, if detected at an early stage.”
The publication has got an Altmetric score of 594. Mikhail (Misha) Blagosklonny realizes that most of readers are willing to understand the very meaning of it. Based on the Altmetric website, the score relates to “how many people have been exposed to and engaged with a scholarly output.” Likewise, the article about melanoma, was used for citations in different news articles 69 times. In addition, it was quoted in 2 online blogs, as well as 25 Tweets on Twitter and 1 Facebook post. FOX23 of Tulsa, Oklahoma has headlined their report on July 20, 2018 as “New blood test could detect skin cancer early”, using the main content of Australia study 
Another Oncotarget’s research with a top score of 476, is “Biomarkers for early diagnosis of malignant mesothelioma: Do we need another moon-shot,”. This study has appeared in 60 news stories, 1 online blog post and 6 Twitter posts. The majority of public may have seen a short overview only, however those who visit Mikhail (Misha) Blagosklonny at Oncotarget, do get useful scientific facts. Oncotarget is glad to have the chance to share with online customers this highly appreciated and high-quality information, that is trustworthy and reliable.

Comments

Post a Comment

Popular posts from this blog

Accelerated aging syndromes, are they relevant to normal human aging

Image
Accelerated aging syndromes, are they relevant to normal human aging Abstract Hutchinson-Gilford Progeria (HGPS) and Werner syndromes are diseases that clinically resemble some aspects of accelerated aging. HGPS is caused by mutations in theLMNA gene resulting in post-translational processing defects that trigger Progeria in children. Werner syndrome, arising from mutations in the WRN helicase gene, causes premature aging in young adults. What are the molecular mechanism(s) underlying these disorders and what aspects of the diseases resemble physiological human aging? Much of what we know stems from the study of patient derived fibroblasts with both mutations resulting in increased DNA damage, primarily at telomeres. However, in vivo patients with Werner's develop arteriosclerosis, among other pathologies. In HGPS patients, including iPS derived cells from HGPS patients, as well as some mouse models for Progeria, vascular smooth muscle (VSM) appears to be among the most severely af
Read more

Progeria, rapamycin and normal aging: recent breakthrough

Image
Progeria, rapamycin and normal aging: recent breakthrough Abstract A recent discovery that rapamycin suppresses a pro-senescent phenotype in progeric cells not only suggests a non-toxic therapy for progeria but also implies its similarity with normal aging. For one, rapamycin is also known to suppress aging of regular human cells. Here I discuss four potential scenarios, comparing progeria with both normal and accelerated aging. This reveals further indications of rapamycin both for accelerated aging in obese and for progeria. In the last week paper in  Science Transl Med , Francis Collins, Dimitri Krainc, Kan Cao and co-workers described that rapamycin reverses cellular phenotypes in Hutchinson-Gilford progeria syndrome (HGPS) cells [ 1 ]. Is it a co-incidence that rapamycin also suppresses senescence in regular (non-HGPS) mammalian cells [ 2 ]? Clearance of progerin by rapamycin Hutchinson-Gilford progeria syndrome (HGPS) is a rare genetic disorder characterized by some features remi
Read more

Genome integrity, stem cells and hyaluronan

Image
Genome integrity, stem cells and hyaluronan Abstract Faithful preservation of genome integrity is the critical mission of stem cells as well as of germ cells. Reviewed are the following mechanisms involved in protecting DNA in these cells: (a) The efflux machinery that can pump out variety of genotoxins in ATP-dependent manner; (b) the mechanisms maintaining minimal metabolic activity which reduces generation of reactive oxidants, by-products of aerobic respiration; (c) the role of hypoxic niche of stem cells providing a gradient of variable oxygen tension; (d) (e) the presence of hyaluronan (HA) and HA receptors on stem cells and in the niche; (f) the role of HA in protecting DNA from oxidative damage; (g) the specific function of HA in protecting DNA in stem cells; (h) the interactions of HA with sperm cells and oocytes that also may shield their DNA from oxidative damage, and (e) mechanisms by which HA exerts the anti-oxidant activity. While HA has multitude of functions its anti-ox
Read more

Disrupting the circadian clock: Gene-specific effects on aging, cancer, and other phenotypes

Image
Disrupting the circadian clock: Gene-specific effects on aging, cancer, and other phenotypes Abstract The circadian clock imparts 24-hour rhythmicity on gene expression and cellular physiology in virtually all cells. Disruption of the genes necessary for the circadian clock to function has diverse effects, including aging-related phenotypes. Some circadian clock genes have been described as tumor suppressors, while other genes have less clear functions in aging and cancer. In this Review, we highlight a recent study [Dubrovsky et al.,  Aging  2: 936-944, 2010] and discuss the much larger field examining the relationship between circadian clock genes, circadian rhythmicity, aging-related phenotypes, and cancer. Introduction In a recent issue of Aging, Dubrovsky et al. [ 1 ] describe the effects of disruption of the Clock gene on lifespan and health in mice. They report that CLOCK-deficient mice have reduced average and maximum lifespan, and have increased incidence of dermatitis and cat
Read more

Indy knockdown in mice mimics elements of dietary restriction.

Image
Indy knockdown in mice mimics elements of dietary restriction. A new mouse knock-out of the Indy gene sheds light on the mechanisms by which a reduction in Indy may lead to a healthier life. Mutations in the Indy gene (for I’m not dead yet) were first described in flies where they dramatically extend life span without a loss in fertility, physical activity, flight velocity or metabolic rate [1, 2]. The Indy gene codes for a high-affinity dicarboxylate/citrate plasma membrane transporter found most abundantly at the plasma membrane of adult fat body, oenocytes and midgut cells, the primary sites of intermediary metabolism in the fly [3]. In support of the hypothesis that the Indy mutation might be altering metabolism in a manner similar to dietary restriction (DR), it has been shown that DR downregulates Indy in normal flies and that Indy long-lived flies share several phenotypes with long-lived DR flies, including decreased insulin-like signaling, lipid storage, weight gain, and resist
Read more

New comparative genomics approach reveals a conserved health span signature across species

Image
New comparative genomics approach reveals a conserved health span signature across species Abstract Environmental and genetic interventions extend health span in a range of organisms by triggering changes in different specific but complementary pathways. We investigated the gene expression changes that occur across species when health span is extended via different interventions. To perform this comparison using heterogeneous datasets from different measurement platforms and organisms, we developed a novel non-parametric methodology that can detect statistical significance of overlaps in ranked lists of genes, and estimate the number of genes with a common expression profile. By comparing genetic and environmental interventions that consistently lead to increased health span in invertebrates and vertebrates we built a conserved health span signature and described how such a signature depends on tissue type. Furthermore, we examined the relationship between calorie restriction and resve
Read more