CLCF1 Exercise-induced Myokine Protocol for Investigating RANKL/OPG Bone Protection Mechanisms in Postmenopausal Osteoporosis

Summary

This article presents a comprehensive protocol for investigating cardiotrophin-like cytokine factor 1 (CLCF1) as an exercise-induced mediator of bone protection through RANKL/OPG axis modulation in postmenopausal osteoporosis.

Abstract

Recent studies have identified cardiotrophin-like cytokine factor 1 (CLCF1) as an exercise-induced "youth molecule" that mediates musculoskeletal benefits, but declines with age. This protocol describes a systematic approach to investigate CLCF1's regulatory role in exercise-mediated bone protection via immune-bone crosstalk mechanisms. The methodology encompasses clinical sample analysis, molecular characterization techniques, and functional assays to elucidate CLCF1's influence on the receptor activator of the nuclear factor-κB ligand (RANKL)/osteoprotegerin (OPG) signaling axis. Through quantitative polymerase chain reaction (qPCR), western blotting, CRISPR/Cas9 gene editing, and co-culture systems, this protocol demonstrates CLCF1's dual bone-protective actions via STAT1-mediated osteoclast inhibition and STAT3-mediated osteoblast promotion. The described methods enable the comprehensive assessment of CLCF1 expression patterns, correlation analyses with bone mineral density parameters, and mechanistic evaluation of potential exercise-mimetic treatment interventions. Unlike traditional antiresorptive therapies that primarily target osteoclasts, CLCF1-based interventions may offer the unique advantage of simultaneously promoting bone formation while inhibiting resorption. This protocol provides researchers with standardized procedures to investigate exercise-induced cytokine-mediated regulation of bone metabolism and facilitates the development of targeted therapeutic interventions for age-related bone disorders.

Introduction

Postmenopausal osteoporosis (PMOP) represents a paradigmatic example of age-related musculoskeletal decline in which immune system dysregulation precipitates pathological bone loss^1,2,3. Although exercise is widely recognized as the most effective non-pharmacological intervention for preventing age-related bone deterioration, the precise molecular mechanisms underlying exercise-induced bone protection have remained elusive until recently⁴. The contemporary understanding of bone metabolism has evolved beyond traditional endocrinological frameworks to en....

Protocol

This protocol has been approved by the institutional research ethics committee (Protocol #2024-CHSD-0156) and adheres to the Declaration of Helsinki principles. All animal procedures complied with the institutional animal care and use committee guidelines (Protocol #2024-037). All the participants provided written informed consent.

1. Clinical sample collection and exercise intervention assessment

1. Participant recruitment and exercise history evaluation
   1. Recruit postmenopausal women aged 55-75 years with a minimum 1-year postmenopausal duration.
   2. Assess detailed exercise history, including frequency, intensit....

Results

Implementation of this protocol successfully demonstrates CLCF1's regulatory role in immune-mediated bone metabolism using multiple experimental approaches. The clinical validation studies show significant downregulation of CLCF1 expression in PMOP patients compared to healthy controls, as demonstrated in Figure 1A, quantitative PCR analysis of peripheral blood mononuclear cells demonstrated that relative CLCF1 mRNA levels were markedly reduced in the PMOP gr.......

Discussion

The protocol described herein provides a comprehensive methodological framework for investigating CLCF1's role as an exercise-induced mediator of bone protection through a systematic analysis of the RANKL/OPG axis. Recent breakthrough research has identified CLCF1 as an exercise-induced factor that combats age-related musculoskeletal decline, positioning it as a central mediator of exercise-induced bone protection^34,35,36. T.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Cell Culture Media & Reagents
Dimethyl Sulfoxide (DMSO)	Sigma-Aldrich	D2650	Purpose_Application:  Cryopreservation medium component Specifications_Comments: Molecular biology grade, sterile filtered
DMEM medium	Thermo Fisher Scientific	11965092	Purpose_Application:  MG-63 osteoblast culture medium Specifications_Comments: High glucose formulation with L-glutamine
Fetal Bovine Serum (FBS)	Thermo Fisher Scientific	16000044	Purpose_Application:  Cell culture supplement (heat-inactivated) Specifications_Comments: Heat-inactivated at 56°C for 30 min
Penicillin-Streptomycin	Thermo Fisher Scientific	15140122	Purpose_Application:  Antibiotic supplement for sterile culture Specifications_Comments: 100X stock, final concentration 1%
Polybrene (Hexadimethrine bromide)	Santa Cruz Biotechnology	sc-134220	Purpose_Application:  Lentiviral transduction enhancer Specifications_Comments: 8 μg/mL working concentration
Puromycin dihydrochloride	InvivoGen	ant-pr-1	Purpose_Application:  Selection antibiotic for transduced cells Specifications_Comments: 4 μg/mL selection concentration for 7 days
RPMI-1640 medium	Thermo Fisher Scientific	11875093	Purpose_Application:  Raji B-lymphocyte culture medium Specifications_Comments: With L-glutamine, without phenol red preferred
Trypan Blue Solution	Thermo Fisher Scientific	15250061	Purpose_Application:  Cell viability assessment Specifications_Comments: 0.4% solution for exclusion assay
Controlled-rate Freezing Container	Thermo Fisher Scientific	5100-0001	Purpose_Application:  Controlled-rate cell freezing (-1°C/min) Specifications_Comments: Mr. Frosty or equivalent for -1°C/min cooling
EDTA Blood Collection Tubes	BD Biosciences	366643	Purpose_Application:  Venous blood collection with anticoagulant Specifications_Comments: 10-20 mL capacity, purple top tubes
Ficoll-Paque PLUS Density Gradient	Cytiva (GE Healthcare)	17144003	Purpose_Application:  PBMC isolation via density centrifugation Specifications_Comments: Sterile, endotoxin-tested for cell separation
Phosphate Buffered Saline (PBS)	Thermo Fisher Scientific	14190144	Purpose_Application:  Cell washing and dilution buffer Specifications_Comments: Sterile, cell culture grade
RNA Extraction & qPCR
Chloroform (ACS Grade)	Sigma-Aldrich	C2432	Purpose_Application:  Phase separation in RNA extraction Specifications_Comments: ACS reagent grade, ≥99% purity
Ethanol (75%, Molecular Grade)	Sigma-Aldrich	E7023	Purpose_Application:  RNA pellet washing Specifications_Comments: Molecular biology grade, prepare fresh
Isopropanol (Molecular Grade)	Sigma-Aldrich	I9516	Purpose_Application:  RNA precipitation Specifications_Comments: Molecular biology grade, ≥99.5% purity
Nuclease-free Water	Thermo Fisher Scientific	AM9930	Purpose_Application:  PCR reaction preparation Specifications_Comments: DNase/RNase-free, tested for PCR applications
Optical Adhesive Film	Thermo Fisher Scientific	4311971	Purpose_Application:  Optical sealing for qPCR plates Specifications_Comments: Optical quality for qPCR applications
PCR Plates (96-well)	Thermo Fisher Scientific	N8010560	Purpose_Application:  96-well format for high-throughput qPCR Specifications_Comments: White, clear bottom for optical detection
PCR Tube Strips	Thermo Fisher Scientific	AB0451	Purpose_Application:  Small volume PCR reactions Specifications_Comments: 8-tube strips with individual caps
PrimeScript RT Reagent Kit	Takara Bio	RR037A	Purpose_Application:  Reverse transcription of RNA to cDNA Specifications_Comments: With gDNA Eraser for genomic DNA removal
SYBR Green Master Mix	Applied Biosystems	4309155	Purpose_Application:  Real-time PCR amplification and detection Specifications_Comments: With ROX reference dye for normalization
TRIzol Reagent (RNA Lysis)	Thermo Fisher Scientific	15596026	Purpose_Application:  Cell lysis and RNA extraction Specifications_Comments: Store at 4°C, use within 6 months
Protein Analysis - Western Blot
Acrylamide/Bis-acrylamide (29:1)	Bio-Rad	1610146	Purpose_Application:  SDS-PAGE gel polymerization Specifications_Comments: 30% acrylamide stock solution
BCA Protein Assay Kit	Thermo Fisher Scientific	23225	Purpose_Application:  Protein concentration quantification Specifications_Comments: Reduce-compatible for accurate quantification
Enhanced Chemiluminescence (ECL) Substrate	Thermo Fisher Scientific	32106	Purpose_Application:  Chemiluminescent protein detection Specifications_Comments: Femtogram sensitivity detection
Non-fat Dry Milk	Lab Scientific	170-6404	Purpose_Application:  Western blot blocking agent Specifications_Comments: Blocking grade, low background
Phosphatase Inhibitor Cocktail	Roche Applied Science	4906845001	Purpose_Application:  Prevent protein dephosphorylation Specifications_Comments: Includes okadaic acid and calyculin A
Prestained Protein Ladder	Bio-Rad	1610394	Purpose_Application:  Molecular weight reference standards Specifications_Comments: 10-250 kDa range with 11 bands
Protease Inhibitor Cocktail	Roche Applied Science	11697498001	Purpose_Application:  Prevent protein degradation during lysis Specifications_Comments: EDTA-free for metal-dependent phosphatases
PVDF Membranes (0.45 μm)	Millipore Sigma	IPVH00010	Purpose_Application:  Protein transfer membrane (0.45 μm pore) Specifications_Comments: Low fluorescence background
RIPA Lysis Buffer	Cell Signaling Technology	9806S	Purpose_Application:  Whole cell protein extraction Specifications_Comments: Ready-to-use lysis buffer with detergents
Sample Loading Buffer (4X)	Bio-Rad	1610747	Purpose_Application:  Protein sample preparation for SDS-PAGE Specifications_Comments: Loading dye with β-mercaptoethanol
SDS-PAGE Running Buffer	Bio-Rad	1610732	Purpose_Application:  Protein electrophoresis Specifications_Comments: Tris-glycine-SDS buffer system
Sodium Fluoride	Sigma-Aldrich	201154	Purpose_Application:  Additional phosphatase inhibition Specifications_Comments: 50 mM working concentration
Sodium Orthovanadate	Sigma-Aldrich	S6508	Purpose_Application:  JAK2/STAT phosphorylation preservation Specifications_Comments: 1 mM working concentration, prepare fresh
Transfer Buffer Concentrate	Bio-Rad	1704156	Purpose_Application:  Semi-dry protein transfer Specifications_Comments: 10X concentrate, dilute before use
Tris-Buffered Saline with Tween-20 (TBST)	Cell Signaling Technology	9997S	Purpose_Application:  Membrane washing and antibody dilution Specifications_Comments: 0.1% Tween-20, pH 7.6
CRISPR/Gene Editing
Calcium Phosphate Transfection Kit	Promega	E1200	Purpose_Application:  DNA transfection into packaging cells Specifications_Comments: High transfection efficiency for lentivirus production
DNA Gel Extraction Kit	Qiagen	28706	Purpose_Application:  PCR product purification for sequencing Specifications_Comments: Column-based purification system
GV371 Lentiviral Vector	GeneChem Co., Ltd	GV371	Purpose_Application:  CRISPR/Cas9 expression for gene knockout Specifications_Comments: Ready-to-use CRISPR/Cas9 lentiviral system
HEK293T Cell Line	ATCC	CRL-3216	Purpose_Application:  Lentiviral packaging cell line Specifications_Comments: Highly transfectable packaging cell line
Sanger Sequencing Service	Macrogen Inc.	Custom	Purpose_Application:  Knockout validation and off-target analysis Specifications_Comments: Standard sequencing with custom primers
T7 Endonuclease I	New England Biolabs	M0302S	Purpose_Application:  CRISPR cutting efficiency validation Specifications_Comments: Mismatch-specific endonuclease for CRISPR validation
ELISA & Immunoassays
ELISA Plates (96-well, flat bottom)	Corning	3590	Purpose_Application:  ELISA substrate reaction Specifications_Comments: High-binding, flat-bottom for ELISA
Human CLCF1 DuoSet ELISA	R&D Systems	DY1234	Purpose_Application:  CLCF1 protein quantification (31.2-2000 pg/mL) Specifications_Comments: Detection range: 31.2-2000 pg/mL, CV & 10%
p24 ELISA Kit (Lentiviral titer)	ZeptoMetrix Corporation	801111	Purpose_Application:  Lentiviral titer determination Specifications_Comments: For lentiviral titer determination (>10⸠TU/mL)
Functional Assays
Alizarin Red S Staining Kit	Sigma-Aldrich	A5533	Purpose_Application:  Calcium deposition visualization Specifications_Comments: 2% solution in distilled water, pH 4.1-4.3
Alkaline Phosphatase Activity Kit	Abcam	ab83369	Purpose_Application:  ALP enzymatic activity measurement Specifications_Comments: Colorimetric assay, read at 405 nm
Ascorbic Acid (L-Ascorbic acid)	Sigma-Aldrich	A4544	Purpose_Application:  Osteogenic medium component Specifications_Comments: 50 μg/mL final concentration
Cetylpyridinium Chloride	Sigma-Aldrich	C9002	Purpose_Application:  Alizarin Red S extraction for quantification Specifications_Comments: 10% solution for dye extraction
Dexamethasone	Sigma-Aldrich	D4902	Purpose_Application:  Osteogenic medium component Specifications_Comments: 10 nM final concentration
β-Glycerophosphate	Sigma-Aldrich	G9422	Purpose_Application:  Osteogenic medium component Specifications_Comments: 10 mM final concentration
Osteogenic Differentiation Medium	PromoCell	C-28010	Purpose_Application:  Osteoblast differentiation induction Specifications_Comments: Ready-to-use complete osteogenic medium
Transwell Cell Culture Inserts (0.4 μm)	Corning	3470	Purpose_Application:  Co-culture system with 0.4 μm separation Specifications_Comments: Polyethylene terephthalate membrane, sterile
Equipment - Major Instruments
Centrifuge (High-speed, Refrigerated)	Eppendorf	5430R	Purpose_Application:  Sample processing and cell separation Specifications_Comments: Refrigerated, max 30,000 x g
Chemiluminescence Imaging System	Bio-Rad Laboratories	12003154	Purpose_Application:  Western blot imaging and quantification Specifications_Comments: Gel documentation and Western blot imaging
CO2 Incubator (Humidified)	Thermo Fisher Scientific	51030287	Purpose_Application:  Cell culture maintenance (37°C, 5% CO2) Specifications_Comments: Triple gas (CO2/O2/N2), humidity control
Heart Rate Monitor (Chest Strap)	Polar Electro	H10	Purpose_Application:  Continuous heart rate monitoring Specifications_Comments: Bluetooth connectivity, ±1 bpm accuracy
Hologic Discovery A DXA Scanner	Hologic Inc.	Discovery A	Purpose_Application:  Bone mineral density measurement Specifications_Comments: With APEX software v4.5, daily QC required
Microplate Reader (Multi-mode)	BioTek Instruments	Synergy H1	Purpose_Application:  ELISA plate reading and absorbance measurement Specifications_Comments: UV-Vis, fluorescence, luminescence detection
Motorized Treadmill	Life Fitness	95Ti	Purpose_Application:  Standardized exercise intervention Specifications_Comments: Variable speed 0-16 km/h, 0-15% grade
Real-time PCR System (CFX96 or equivalent)	Bio-Rad Laboratories	1855195	Purpose_Application:  Real-time PCR amplification and detection Specifications_Comments: 96-well block, gradient capable
Software & Analysis Tools
APEX Software v4.5 (DXA Analysis)	Hologic Inc.	v4.5	Purpose_Application:  DXA scan analysis and BMD calculation Specifications_Comments: BMD analysis with reference database
Bio-Rad CFX Maestro	Bio-Rad Laboratories	CFX Maestro	Purpose_Application:  qPCR data analysis and Ct determination Specifications_Comments: Real-time PCR analysis and data export
GraphPad Prism v9.0	GraphPad Software	v9.0	Purpose_Application:  Statistical analysis and graph generation Specifications_Comments: Statistical software with graph generation
ImageJ/Fiji v1.53	National Institutes of Health	v1.53	Purpose_Application:  Western blot densitometry and image analysis Specifications_Comments: Image analysis with measurement tools
Microsoft Excel 365	Microsoft Corporation	365	Purpose_Application:  Data organization and basic calculations Specifications_Comments: Data organization and basic statistical functions
Consumables & Plasticware
1.5 mL Microcentrifuge Tubes	Eppendorf	22363204	Purpose_Application:  Small volume sample storage and processing Specifications_Comments: DNase/RNase-free, low-binding
15 mL Conical Tubes	Corning	430766	Purpose_Application:  Medium volume sample processing Specifications_Comments: Polypropylene, graduated, with caps
24-well Cell Culture Plates	Corning	3524	Purpose_Application:  Co-culture and functional assay setup Specifications_Comments: Tissue culture treated, flat bottom
50 mL Conical Tubes	Corning	430829	Purpose_Application:  Large volume sample collection and processing Specifications_Comments: Polypropylene, graduated, with caps
Cryovials (1 mL)	Thermo Fisher Scientific	375418	Purpose_Application:  Long-term cell and sample storage at -80°C Specifications_Comments: External thread, O-ring seal, -196°C rated
Pasteur Pipettes (Sterile)	Fisher Scientific	13-678-20A	Purpose_Application:  Sterile sample collection and transfer Specifications_Comments: Individually wrapped, sterile