Growth Factors

Key Biological Properties: hPL shares significant homology with human growth hormone (hGH) and human prolactin (hPRL) . It is a protein hormone with a molecular mass of approximately 22,125 Da, consisting of a single chain of 191 amino acids linked by two disulfide bonds .

Expression Patterns: hPL is synthesized and secreted by the syncytiotrophoblast cells of the placenta . Its levels increase progressively throughout pregnancy, peaking near term .

Tissue Distribution: hPL is primarily found in the placenta and maternal serum during pregnancy .

Primary Biological Functions: hPL plays a crucial role in regulating maternal metabolism to ensure an adequate supply of nutrients to the fetus . It promotes lipolysis, leading to increased free fatty acids for maternal energy use, while sparing glucose for fetal use . hPL also stimulates mammary gland development in preparation for lactation .

Role in Immune Responses and Pathogen Recognition: While hPL’s primary functions are metabolic and lactogenic, it may also have immunomodulatory effects, although this area requires further research .

Mechanisms with Other Molecules and Cells: hPL interacts with prolactin receptors and, to a lesser extent, growth hormone receptors . It mimics the actions of prolactin in various tissues, including the mammary glands .

Binding Partners and Downstream Signaling Cascades: hPL binds to prolactin receptors with high affinity, activating downstream signaling pathways that promote mammary gland development and metabolic adaptations .

Regulatory Mechanisms: The expression of hPL is tightly regulated at both the transcriptional and post-transcriptional levels . Transcriptional regulation involves various nuclear hormone receptors and cytokines that activate the hPL promoter . Post-translational modifications, such as glycosylation, may also play a role in hPL’s stability and activity .

Biomedical Research: hPL is used as a marker for placental function and fetal well-being in pregnancy . It is also studied for its role in metabolic adaptations during pregnancy and its potential implications in gestational diabetes .

Diagnostic Tools: Measurement of hPL levels in maternal serum can help assess placental function and detect potential complications such as placental insufficiency .

Therapeutic Strategies: While not directly used as a therapeutic agent, understanding hPL’s role in pregnancy can inform strategies to manage gestational diabetes and other metabolic disorders .

Role Throughout the Life Cycle: hPL is exclusively produced during pregnancy, with its levels rising in correlation with fetal and placental growth . It plays a vital role in fetal development by ensuring an adequate nutrient supply and preparing the maternal body for lactation . After childbirth, hPL levels rapidly decline .