SHLP2

SHLP2 (small humanin-like peptide 2) is a 26-amino-acid mitochondrial-derived peptide (MDP) encoded by a small open reading frame within the MT-RNR2 gene of human mitochondrial DNA, the same locus that encodes the 16S ribosomal RNA and the prototypical MDP humanin. SHLP2 was identified in 2016 through in silico screening of the MT-RNR2 region for conserved peptide-coding sequences in the laboratory of Pinchas Cohen at the University of Southern California Leonard Davis School of Gerontology. Among the six small humanin-like peptides (SHLP1 through SHLP6) characterized in the discovery report, SHLP2 emerged as the most biologically active member, demonstrating cytoprotective, anti-apoptotic, insulin-sensitizing, and neuroprotective properties that partially overlap with but are mechanistically distinct from those of humanin and MOTS-c.

The molecular pharmacology of SHLP2 centers on agonism of the atypical chemokine receptor CXCR7 (ACKR3), identified through high-throughput PathHunter beta-arrestin screening of 168 G-protein-coupled receptors, with SHLP2 recruiting beta-arrestin 2 to CXCR7 at approximately 70 percent of the efficacy of the endogenous ligand SDF-1alpha/CXCL12 and a calculated EC50 of 0.97 micromolar. Downstream signaling proceeds through MAPK/ERK1/2 phosphorylation and STAT3 activation, with the ERK pathway required for SHLP2-induced depolarization of hypothalamic pro-opiomelanocortin (POMC) neurons. In addition to receptor-mediated signaling, SHLP2 binds directly to the proton-pumping Pd modules of mitochondrial complex I, functions as a molecular chaperone that inhibits amyloidogenic seed propagation, and modulates oxidative phosphorylation complex protein subunit expression.

Preclinical pharmacology spans multiple disease-relevant models. In energy homeostasis, both systemic (2 mg/kg intraperitoneal) and central (3 micrograms intracerebroventricular) SHLP2 administration protects male mice from high-fat-diet-induced obesity through POMC neuron activation, suppression of food intake, promotion of brown adipose tissue thermogenesis, and improvement of insulin sensitivity demonstrated by hyperinsulinemic-euglycemic clamp. In neuroprotection, SHLP2 prevents amyloid-beta-induced neuronal death in primary cortical cultures and, as the naturally occurring K4R variant (m.2158 T>C), reduces Parkinson's disease risk (odds ratio 0.45 in Caucasian cohorts) and protects dopaminergic neurons in MPTP mouse models. In retinal disease, SHLP2 at 3.2 micromolar restores oxidative phosphorylation complex subunit levels, increases mitochondrial DNA copy number, reduces caspase-3 and caspase-7 expression, and attenuates amyloid-beta-induced toxicity in transmitochondrial ARPE-19 cybrids derived from age-related macular degeneration patients. In metabolic disease, SHLP2 inhibits islet amyloid polypeptide fibrilization through chaperone-like seed-binding activity and delays the onset of type 2 diabetes mellitus in high-fat-diet plus streptozotocin mouse models.

Circulating SHLP2 levels decline with age in both murine and human plasma, are lower in obese and diabetic individuals, and show sex-dependent differences (males higher than females). The peptide crosses the blood-brain barrier following systemic administration, producing c-Fos activation in the hypothalamic arcuate nucleus and dorsomedial hypothalamus. No human clinical trials of exogenous SHLP2 administration have been completed or registered as of the monograph revision date. CohBar, Inc. (now CWBR) holds the exclusive license for therapeutic development of the SHLP family. Research-grade SHLP2 is synthesized by solid-phase Fmoc chemistry, purified by reverse-phase HPLC to greater than 95 percent purity, and confirmed by MALDI-TOF mass spectrometry. This monograph reviews the identification, molecular pharmacology, preclinical evidence base, sourcing, handling, stack-interaction considerations, safety signal, and comparative positioning of SHLP2 against four related mitochondrial-derived peptides and one structurally analogous cytoprotective peptide on five competency standards.