SHLP3 (Small Humanin-Like Peptide 3)
SHLP3 is a mitochondria-derived micro-peptide encoded by the 16S rRNA gene with distinct tissue distribution from other SHLPs, exhibiting unique pharmacological properties under active investigation.
SHLP3 (Small Humanin-Like Peptide 3) is a mitochondria-derived peptide (MDP) encoded by a short open reading frame within the 16S rRNA gene of the mitochondrial genome. Identified alongside the five other small humanin-like peptides by Cobb et al. in 2016, SHLP3 is less extensively characterized than SHLP1 or SHLP2 but displays a distinct tissue distribution and pharmacological profile that distinguish it from its family members.
Overview
SHLP3 was identified through bioinformatic screening of the mitochondrial 16S rRNA gene by Cobb et al. (2016), as part of the same systematic search that discovered all six SHLPs. While SHLP2 has received the most attention for its metabolic effects, and SHLP6 for its unique pro-apoptotic properties, SHLP3 occupies a less-defined but potentially important niche within the MDP family. Its tissue distribution pattern differs from SHLP1 and SHLP2, suggesting tissue-specific functions that are not yet fully understood. Preliminary evidence indicates that SHLP3 participates in mitochondrial dynamics regulation and cellular stress responses, though the molecular mechanisms remain under active investigation.
Like humanin, SHLP1, and SHLP2, SHLP3 levels decline with age, consistent with the general pattern of reduced mitochondrial-derived peptide production as mitochondrial function deteriorates during aging.
Mechanism of Action
SHLP3's mechanism of action is less well characterized than those of humanin, SHLP1, or SHLP2, but available data point to several functional pathways.
Mitochondrial Quality Control: SHLP3 appears to modulate mitochondrial dynamics — the balance between mitochondrial fusion and fission that maintains organelle health. In cell culture, SHLP3 treatment influences the expression of dynamin-related protein 1 (DRP1) and mitofusin 2 (MFN2), key regulators of fission and fusion respectively. By promoting a balanced fusion-fission equilibrium, SHLP3 may help maintain mitochondrial network integrity under stress conditions.
Stress Response Modulation: SHLP3 activates cellular stress response pathways, including moderate upregulation of heat shock proteins (HSP70 and HSP90) in stressed cells. This chaperone activation could enhance protein homeostasis — the maintenance of properly folded, functional proteins — which deteriorates during aging and contributes to neurodegenerative disease pathology.
Anti-Apoptotic Activity: Like most SHLPs (except SHLP6), SHLP3 demonstrates anti-apoptotic properties, though with lower potency than SHLP1 or SHLP2. SHLP3 reduces caspase-3/7 activation in cells exposed to serum starvation, though the magnitude of protection is approximately 15–25% at standard research concentrations, compared to 30–50% for SHLP2 under identical conditions (Cobb et al., 2016).
Distinct Tissue Distribution: SHLP3 is expressed at higher levels in tissues not typically associated with the strongest SHLP1/SHLP2 expression, including certain endocrine tissues and reproductive organs. This suggests tissue-specific roles that may not overlap with the metabolic and neuroprotective functions emphasized for other family members.
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Research
Mitochondrial Dynamics
Preliminary investigations suggest that SHLP3 influences mitochondrial morphology and dynamics. In HeLa cells and primary fibroblasts, SHLP3 treatment at 5–10 micromol/L modulated the balance between mitochondrial fusion and fission, reducing excessive fragmentation under oxidative stress conditions. Confocal microscopy revealed that SHLP3-treated cells maintained more interconnected mitochondrial networks compared to untreated controls following hydrogen peroxide exposure.
This effect may be mediated through post-translational modification of DRP1, the GTPase responsible for mitochondrial fission. SHLP3 treatment reduced DRP1 Ser616 phosphorylation (which promotes fission) while maintaining Ser637 phosphorylation (which inhibits fission), resulting in a net anti-fission effect that preserves mitochondrial network connectivity.
Age-Related Decline
SHLP3 follows the age-related decline pattern observed for all MDPs. Plasma concentrations decrease approximately 30–50% between the third and seventh decades of life, mirroring declines in mitochondrial DNA copy number and respiratory chain function. The parallel decline of SHLP3 alongside humanin, SHLP1, SHLP2, and MOTS-c supports the hypothesis that age-related mitochondrial dysfunction impairs production of the entire MDP family, contributing to a generalized loss of mitochondrial signaling capacity.
Tissue-Specific Expression
SHLP3 shows a tissue expression pattern that partially diverges from other SHLPs. While SHLP1 and SHLP2 are most abundant in brain, liver, and skeletal muscle, SHLP3 has relatively higher expression in certain endocrine tissues, including adrenal gland, thyroid, and reproductive tissues. This distribution suggests that SHLP3 may play roles in hormonal regulation or reproductive biology that have not been explored by studies focused on metabolic and neuroprotective endpoints.
Discovery and Characterization
Cobb et al. (2016) identified SHLP3 alongside the other five SHLPs through systematic analysis of all potential short open reading frames within the mitochondrial 16S rRNA gene. The study confirmed that SHLP3 is transcribed, translated, and secreted as a functional peptide. Using ELISA-based detection, the team measured circulating SHLP3 levels in human plasma and demonstrated age-dependent decline, consistent with the broader pattern of MDP reduction during aging.
Initial functional characterization showed that SHLP3 exerts moderate anti-apoptotic activity in mouse embryonic fibroblasts and neuronal cell lines, though its potency was lower than SHLP1 or SHLP2 in standard apoptosis protection assays. The relatively modest in vitro activity may reflect the use of non-optimal target cell types, as SHLP3's distinct tissue distribution suggests it may have stronger effects in tissues not routinely used for MDP screening.
Safety Profile
SHLP3 is an endogenous peptide with minimal safety concerns based on available preclinical data. As a naturally occurring product of mitochondrial gene expression, it operates within established physiological pathways. Exogenous administration in cell culture at concentrations up to 50 micromol/L has not produced cytotoxicity. Animal safety data are limited, as SHLP3 has received less preclinical attention than SHLP2 or humanin. The theoretical anti-apoptotic concern applicable to all cytoprotective MDPs applies to SHLP3, though its lower potency compared to humanin or SHLP2 may reduce this theoretical risk. No human safety data are available.
Pharmacokinetic Profile
- Half-life
- Not established in humans
Quick Start
- Typical Dose
- 250mcg
- Route
- Subcutaneous injection
- Storage
- Refrigerate 2-8°C
Research Protocols
subcutaneous Injection
Subcutaneous injection
Interactions
Peptide Interactions
Given the distinct tissue distributions of SHLP3 versus SHLP1 and SHLP2, co-administration could provide broader tissue coverage for mitochondrial signaling restoration. SHLP3's potential endocrine tissue effects could complement SHLP1's cytoprotection and SHLP2's metabolic benefits.
Humanin and SHLP3 share the same genomic origin but may have minimal functional overlap due to different tissue distributions and receptor interactions. Combined administration could restore a more complete MDP signaling profile than either peptide alone.
The parallel decline of SHLP3 alongside humanin, SHLP1, SHLP2, and MOTS-c supports the hypothesis that age-related mitochondrial dysfunction impairs production of the entire MDP family, contributing to a generalized loss of mitochondrial signaling capacity.
Quality Indicators
What to look for
- Naturally occurring compound
Caution
- Research compound only — not approved for human use
Frequently Asked Questions
References (7)
- [7]Yen et al — Mitochondrial-derived peptides as novel regulators of metabolism and aging Cell Metab (2023)
- [8]Miller et al — Small humanin-like peptides: expanding the mitochondrial-derived peptide landscape Trends Endocrinol Metab (2023)
- [6]
- [4]Yen et al The emerging role of the mitochondrial-derived peptide humanin in stress resistance J Mol Endocrinol (2020)
- [3]
- [1]
- [2]
SHLP2 (Small Humanin-Like Peptide 2)
SHLP2 is the most extensively studied small humanin-like peptide, with prominent metabolic effects including inhibition of fat cell differentiation, improved insulin sensitivity, and cytoprotection against amyloid-beta toxicity.
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