Cardiotrophin-1 (CT-1) is one of those molecules that keeps showing up whenever researchers ask a sharper question about the heart. It was first isolated in the mid-1990s as a soluble factor that made cultured cardiac muscle cells grow larger, and it has since been recognized as a full member of the interleukin-6 (IL-6) family of cytokines. Unlike the cardiac natriuretic peptides, which are released in response to stretch and act as endocrine "volume" signals, CT-1 behaves more like a stress-and-survival cytokine: cardiomyocytes and cardiac fibroblasts ramp it up under mechanical load, angiotensin II, ischemia, or inflammatory pressure, and it then feeds back into both protective and maladaptive remodeling. The questions people actually type into a search bar tend to be concrete rather than textbook — what does a high cardiotrophin-1 level mean, how is CT-1 different from BNP or NT-proBNP, is it a useful heart-failure marker, and can you actually measure it reliably in serum? Those are the questions this review is built to answer.

Quantifying the CT-1 axis means measuring the cytokine itself, its close IL-6-family relatives, and the intracellular machinery it activates — each answers a different part of the same biological question. Our portfolio supports that workflow with ELISA kits for CT-1 protein, the related cytokine CLCF1/CLC, total and phosphorylated STAT3, and gp130/LIFR activation readouts, plus matched antibody pairs for custom immunoassay development and activity-style reagents for profiling IL-6-family signaling. For groups mapping the full cardiokine landscape, the same platform can track CT-1 together with downstream transcription-factor activation, so a single study can connect secreted ligand, receptor engagement, and nuclear response without switching assays.

The IL-6 Family Context and How Cardiotrophin-1 Signals

CT-1 is a secreted glycoprotein of roughly 21 kDa that belongs to the same cytokine family as IL-6, IL-11, leukemia inhibitory factor (LIF), oncostatin M, ciliary neurotrophic factor, and the cardiotrophin-like cytokine CLCF1. What unites the family is not sequence alone but a shared signaling subunit: glycoprotein 130 (gp130). CT-1 binds as a ligand to a receptor complex built from gp130 paired with the leukemia inhibitory factor receptor β (LIFRβ). Ligand engagement brings the intracellular domains of these chains together, recruiting Janus kinases (JAK1 and JAK2) that phosphorylate tyrosine residues on the receptors and on themselves, creating docking sites for STAT3. Phosphorylated STAT3 dimerizes, translocates to the nucleus, and drives the transcriptional program behind both cardiomyocyte hypertrophy and cell-survival genes. A parallel MAPK/ERK limb, wired through the same receptor, handles the anti-apoptotic and neurotrophic effects. That dual wiring is the key to understanding CT-1's double life: the same receptor can promote growth and protect the cell, depending on context and duration of signal.

This is worth separating from the natriuretic-peptide world. BNP and ANP signal through natriuretic-peptide receptors with intracellular guanylate cyclase activity and act largely as endocrine brakes on volume and pressure overload. CT-1 signals through JAK/STAT and is produced locally by the myocardium and by non-cardiac tissues alike. Clinically, that means a rising CT-1 and a rising BNP are not redundant readouts — they capture overlapping but distinct biology, which is exactly why combining them has consistently outperformed either alone in risk prediction.

Key Molecules in the Cardiotrophin Axis

Cardiotrophin-1 (CT-1 / CTF1 gene)

Encoded by the CTF1 gene, CT-1 is the ligand at the center of this review. It is induced by biomechanical stress, neurohumoral agonists such as angiotensin II, and inflammatory cytokines, and it is expressed not only in heart but also in liver, kidney, skeletal muscle, testis, nervous tissue, and many tumors. Circulating levels rise in hypertensive heart disease, acute myocardial infarction, chronic systolic and diastolic heart failure, and a growing list of non-cardiac conditions. Because the mature protein is small and stable in serum, it is tractable to immunoassay, but units matter: most clinical reports express CT-1 in fmol/mL, which is not interchangeable with the pg/mL scales used for natriuretic peptides, so reference ranges must be read against the assay's own standard.

Cardiotrophin-like cytokine (CLC / CLCF1)

CLCF1 — historically called novel neurotrophin-1 or B-cell-stimulating factor-3 before being standardized as cardiotrophin-like cytokine — is CT-1's closest structural relative in the family. It is not a free cytokine; it is secreted as a heterodimer with cytokine receptor-like factor 1 (CRLF1) and then engages a tripartite receptor made of CRLF1, CLCF1, and the ciliary neurotrophic factor receptor (CNTFR) to activate gp130-dependent STAT3 signaling. Loss of this axis in development causes motor-neuron loss and the cold-induced sweating syndromes in humans, while in adult tissues CLCF1 is increasingly implicated in immune regulation, bone, and metabolic control. Including CLCF1 alongside CT-1 helps distinguish which arm of the IL-6 family is actually engaged in a given sample.

gp130 (IL6ST)

Glycoprotein 130 is the common signal-transducing subunit for essentially every IL-6-family cytokine, CT-1 included. It carries no ligand-binding specificity of its own but provides the intracellular Box1/Box2 motifs that recruit JAK family kinases. Measuring total gp130 tells you about receptor abundance; measuring phosphorylated (activated) gp130, or the downstream phosphorylated STAT3 it drives, tells you whether the pathway is actually firing. For CT-1 mechanistic studies, a phosphorylated-STAT3 or phosphorylated-gp130 readout is the functional counterpart to the ligand ELISA — the difference between "the cytokine is present" and "the cytokine is doing something."

LIFR (Leukemia inhibitory factor receptor β)

LIFRβ is the partner chain that converts the gp130 platform from a generic homodimer into the CT-1-specific receptor complex. Experimental work in the late 1990s showed that blocking gp130 or antagonizing LIFRβ both suppress the CT-1 hypertrophic response in cardiomyocytes, confirming that signaling runs through the gp130/LIFRβ heterodimer rather than gp130 alone. In practice, LIFR status matters when you need to separate CT-1-driven effects from those of IL-6 or IL-11, which can signal through gp130 paired with different α-receptors. A receptor-composition view — which α-chain is present — often explains why two IL-6-family members produce different outcomes in the same cell.

STAT3

Signal transducer and activator of transcription 3 is the transcription factor that converts CT-1 receptor engagement into changed gene expression. In cardiac myocytes, STAT3 activation drives the hypertrophic gene program (including atrial natriuretic factor) and, on a separate limb, protects against apoptosis through MAPK-dependent survival signaling. Because STAT3 sits at the convergence of many cytokines, phosphorylated-STAT3 is a sensitive but non-specific marker of IL-6-family activity; it is most informative when paired with a ligand-specific measure such as CT-1 ELISA. The ratio of active to total STAT3, rather than total STAT3 alone, is what tracks with pathway output.

IL-6-family comparators (IL-6, IL-11, LIF, OSM, CNTF)

No CT-1 interpretation is complete without the rest of the family. IL-6 and IL-11 share the gp130 machinery through their own α-receptors; LIF and OSM overlap directly with CT-1 at the LIFRβ/gp130 node; CNTF signals through CNTFR with CLCF1 as its ligand partner. In heart-failure and inflammatory cohorts these cytokines often move together, which is why multi-analyte panels that include CT-1 plus IL-6 (and, where relevant, CLCF1) give a fuller picture of cardiokine burden than any single marker. The practical takeaway for assay design is to treat CT-1 as one node in a network, not as a standalone number.

Cardiotrophin-1 in Heart Failure and Cardiac Hypertrophy

The strongest clinical signal around CT-1 is in cardiac stress and failure. Multiple cohorts show circulating CT-1 climbing with New York Heart Association class, with left-ventricular mass, and inversely with ejection fraction. In hypertensive heart disease, CT-1 rises early — before overt hypertrophy is visible — and tracks with progression from normal hearts through left-ventricular hypertrophy to symptomatic stage C heart failure. A frequently cited advantage is complementarity with natriuretic peptides: in one post-infarction study, CT-1 and NT-proBNP each independently predicted death or heart failure, and their combination reached a considerably higher diagnostic accuracy than either marker alone. More recent work in asymptomatic hypertensive patients with mild diastolic dysfunction found CT-1 elevated even when conventional markers were not, supporting its potential as an early-warning biomarker in the transition toward heart failure with preserved ejection fraction.

What a high CT-1 actually means in the clinic is therefore context-dependent. In acute coronary syndrome it adds prognostic information on top of NT-proBNP; in hypertension it flags early maladaptive remodeling; in established heart failure it tracks with severity and adverse events. It is not a replacement for BNP or NT-proBNP — those remain the front-line, guideline-endorsed markers — but as an add-on it answers a different question: not "is the heart stretched" but "is the myocardium mounting a stress-and-remodeling cytokine response." That distinction is why combination panels keep performing better.

Figure 1. Intracellular signal transduction of cardiotrophin-1 (CT-1) in cardiovascular responses. (Source: Watanabe T, et al. 2018)

Beyond the Heart: Kidney, Liver, Nerves, and Tumors

CT-1's name is a historical accident of where it was discovered, not a limit on where it acts. In the kidney, research using gene-deficient mice showed that endogenous CT-1 opposes renal fibrosis: animals lacking the cytokine developed more inflammation, tubular damage, and collagen deposition after ureteral obstruction, and supplying exogenous CT-1 reduced that fibrosis. Follow-up work extended the same protective theme to models of glomerular injury, where CT-1 administration lowered disease severity. These findings reframe CT-1 not just as a cardiac stress marker but as a candidate tissue-protective signal in chronic kidney disease — a useful reminder that a "high" level can sometimes reflect a beneficial endogenous response rather than pure pathology.

In the nervous system, CT-1 is a recognized survival factor for motor and sensory neurons, and its muscle-derived form is required for the survival of specific developing motoneuron populations — the basis for interest in neurodegenerative contexts. The liver angle is equally old: CT-1 was shown early on to stimulate acute-phase responses in hepatocytes, placing it among the cytokines that coordinate systemic inflammation. On the cancer side, tumor-derived CTF1 has been reported to drive stromal-assisted, autophagy-dependent migration and invasion in breast cancer, and CT-1 appears in the secretome of several other malignancies, suggesting it can act as a pro-tumor cardiokine in the tumor microenvironment. The through-line is that CT-1 is a pleiotropic cytokine whose "good" or "bad" readout depends entirely on tissue and timing.