Regulation of Stem Cells by the Endocannabinoid System

“The endocannabinoids, endogenous lipid mediators of related chemical structure to the prototype exogenous cannabinoid Δ9-THC found in marijuana, have emerged as important mediators that regulate central and peripheral neural functions as well as immune responses.

Endogenous and exogenous cannabinoid ligands bind to cannabinoid receptors: the predominant central cannabinoid receptor type 1 (CB1) and the peripheral cannabinoid receptor type 2 (CB2). CB1 and CB2 are members of the G-protein coupled receptor family.

Cannabinoids were shown to modulate the immune system and to affect the migration of blood cells, such as T-cells, monocytes and myeloid leukemia cells, through CB receptors.

Recent data indicate the potential role of cannabinoid ligands and receptors in the regulation of hematopoiesis and hematopoietic stem cell (HSC) migration and trafficking.

These studies may lead to clinical applications of cannabinoid-based compounds as new HSC-mobilizer agents for therapeutic intervention in bone marrow failure.”

Cannabinoid receptor signaling in progenitor/stem cell proliferation and differentiation.

“Cannabinoids, the active components of cannabis (Cannabis sativa) extracts, have attracted the attention of human civilizations for centuries, much earlier than the discovery and characterization of their substrate of action, the endocannabinoid system (ECS).

The latter is an ensemble of endogenous lipids, their receptors [in particular type-1 (CB1) and type-2 (CB2) cannabinoid receptors] and metabolic enzymes.

Cannabinoid signaling regulates cell proliferation, differentiation and survival, with different outcomes depending on the molecular targets and cellular context involved.

Cannabinoid receptors are expressed and functional from the very early developmental stages, when they regulate embryonic and trophoblast stem cell survival and differentiation, and thus may affect the formation of manifold adult specialized tissues derived from the three different germ layers (ectoderm, mesoderm and endoderm).

In the ectoderm-derived nervous system, both CB1 and CB2 receptors are present in neural progenitor/stem cells and control their self-renewal, proliferation and differentiation. CB1 and CB2 show opposite patterns of expression, the former increasing and the latter decreasing along neuronal differentiation.

Recently, endocannabinoid (eCB) signaling has also been shown to regulate proliferation and differentiation of mesoderm-derived hematopoietic and mesenchymal stem cells, with a key role in determining the formation of several cell types in peripheral tissues, including blood cells, adipocytes, osteoblasts/osteoclasts and epithelial cells.

Here, we will review these new findings, which unveil the involvement of eCB signaling in the regulation of progenitor/stem cell fate in the nervous system and in the periphery.

The developmental regulation of cannabinoid receptor expression and cellular/subcellular localization, together with their role in progenitor/stem cell biology, may have important implications in human health and disease.”

CB2 cannabinoid receptors promote mouse neural stem cell proliferation.

“Neurospheres are clonal cellular aggregates of neural stem/precursor cells that grow in culture as free-floating clusters. Activation of CB1 cannabinoid receptors, which are expressed by these cells, promotes proliferation.

In the present study we investigated the expression of CB2 cannabinoid receptors and the effect of exogenous cannabinoids on neural stem/precursor cell proliferation.

Neurospheres containing nestin-positive and sn-1 diacylglycerol lipase alpha-positive cells expressed both CB1 and CB2 receptors, which were maintained through several passages…

Together, our results suggest that cannabinoids stimulate proliferation of neural stem/precursor cells acting on both CB1 and CB2 cannabinoid receptors through a phosphoinositide-3 kinase/Akt pathway.”

Cannabinoid receptor 2 and its agonists mediate hematopoiesis and hematopoietic stem and progenitor cell mobilization.

“Endocannabinoids are arachidonic acid derivatives and part of a novel bioactive lipid signaling system, along with their G-coupled cannabinoid receptors (CB₁ and CB₂) and the enzymes involved in their biosynthesis and degradation.

However, their roles in hematopoiesis and hematopoietic stem and progenitor cell (HSPC) functions are not well characterized. Here, we show that bone marrow stromal cells express endocannabinoids (anandamide and 2-arachidonylglycerol), whereas CB₂ receptors are expressed in human and murine HSPCs.

On ligand stimulation with CB₂ agonists, CB₂ receptors induced chemotaxis, migration, and enhanced colony formation of bone marrow cells, which were mediated via ERK, PI3-kinase, and Gαi-Rac1 pathways.

Taken together, these results demonstrate that the endocannabinoid system is involved in hematopoiesis and that CB₂/CB₂ agonist axis mediates repopulation of hematopoiesis and mobilization of HSPCs.

Thus, CB₂ agonists may be therapeutically applied in clinical conditions, such as bone marrow transplantation.”

CB2 receptor activation prevents glial-derived neurotoxic mediator production, BBB leakage and peripheral immune cell infiltration and rescues dopamine neurons in the MPTP model of Parkinson’s disease

“Parkinson’s disease (PD) is characterized by the degeneration of nigrostriatal dopamine neurons.

The endocannabinoid system consists of cannabinoid receptors, their ligands and enzymes for the synthesis and degradation of cannabinoids.

Our results suggest that targeting the cannabinoid system may be beneficial for the treatment of neurodegenerative diseases, such as PD, that are associated with glial activation, BBB disruption and peripheral immune cell infiltration.

In summary, we demonstrated that activation of the CB2 receptor inhibits BBB damage, the expression of iNOS and proinflammatory cytokines/chemokines in activated microglia, the infiltration of T cells and astroglial expression of MPO, resulting in the survival of dopamine neurons in vivo in the MPTP mouse model of PD.

Therefore, it is likely that targeting the CB2 receptor may have therapeutic value in the treatment of aspects of PD related to neuroinflammation.”

Up-regulation of immunomodulatory effects of mouse bone-marrow derived mesenchymal stem cells by tetrahydrocannabinol pre-treatment involving cannabinoid receptor CB2.

“Chronic pain is commonly and closely correlated with inflammation.

Both cannabinoid signaling and mesenchymal stem cells (MSCs) have been demonstrated to reduce inflammatory pain.

Although cannabinoid signaling is essential for mesenchymal stem cell survival and differentiation, little is known about its role in modulatory effect of MSCs on inflammation and pain sensitivity. Here we showed that mouse bone-marrow derived MSCs (BM-MSCs) expressed both cannabinoid receptor type 1 and 2 (CB1 and CB2). CB2 expression level in BM-MSCs increased with their maturation.

In addition, we found that tetrahydrocannabinol (THC) activated CB2 receptor and ERK signaling, consequently enhancing the modulation of MSCs on inflammation-associated cytokine release from lipopolysaccharides-stimulated microglia.

Consistent with in vitro data, THC pretreatment enhanced the immunomodulatory effects of BM-MSC on thermal hyperalgesia and mechanical allodynia in chronic constriction injury model, by decreasing the release of pro-inflammation cytokines.

Our study revealed the crucial role of THC in promoting the immunomodulatory effects of MSCs and proposed a new strategy to alleviate pain based on stem cells therapy.”

Dronabinol increases pain threshold in patients with functional chest pain: a pilot double-blind placebo-controlled trial.

“Noncardiac chest pain is associated with poor quality of life and high care expenditure. The majority of noncardiac chest pain is either gastresophageal reflux disease related or due to esophageal motility disorders, and the rest are considered functional chest pain (FCP) due to central and peripheral hypersensitivity. Current treatment of FCP improves 40-50% of patients.

Cannabinoid receptors 1 (CB1 ) and 2 (CB2 ) modulate release of neurotransmitters; CB1 is located in the esophageal epithelium and reduces excitatory enteric transmission and potentially could reduce esophageal hypersensitivity.

We performed a prospective study to evaluate its effects on pain threshold, frequency, and intensity in FCP.

Dronabinol increased pain thresholds significantly (3.0 vs. 1.0; P = 0.03) and reduced pain intensity and odynophagia compared to placebo (0.18 vs. 0.01 and 0.12 vs. 0.01, respectively, P = 0.04).

Depression and anxiety scores did not differ between the groups at baseline or after treatment.

No significant adverse effects were observed.

In this novel study, dronabinol increased pain threshold and reduced frequency and intensity of pain in FCP. Further, large scale studies are needed to substantiate these findings.”

Marijuana Use is Not Associated with Cervical Human Papillomavirus Natural History or Cervical Neoplasia in HIV-Seropositive or HIV-Seronegative Women

“Laboratory data suggest that marijuana could have an immunomodulatory effect.

Little is known, however, regarding the effects of marijuana use on cervical HPV or neoplasia. Therefore, we studied the natural history (i.e., prevalence, incident detection, clearance/persistence) of cervical HPV and cervical neoplasia (i.e., squamous intraepithelial lesions; SIL) in a large prospective cohort of 2,584 HIV-seropositive and 915 HIV-seronegative women.

No positive associations were observed between use of marijuana, and either cervical HPV infection or SIL. The findings were similar among HIV-seropositive and HIV-seronegative women, and in tobacco smokers and nonsmokers. These data suggest that marijuana use does not increase the burden of cervical HPV infection or SIL.

In summary, our investigation found no positive associations between marijuana use and cervical HPV or SIL. These findings are comforting given the high prevalence of marijuana use in HIV-seropositive and other populations…”

Prior Cannabis Use Is Associated with Outcome after Intracerebral Hemorrhage.

“The purpose of this study was to determine the implications of cannabis use in intracerebral hemorrhage (ICH) patients.


In this multinational cohort, cannabis use was discovered in nearly 10% of patients with spontaneous ICH. Although there was no relationship between cannabis use and specific ICH characteristics, CB+ patients had milder ICH presentation and less disability at discharge.”

CB2 Cannabinoid Receptor Knockout in Mice Impairs Contextual Long-Term Memory and Enhances Spatial Working Memory.

“Neurocognitive effects of cannabinoids have been extensively studied with a focus on CB1 cannabinoid receptors because CB1 receptors have been considered the major cannabinoid receptor in the nervous system. However, recent discoveries of CB2 cannabinoid receptors in the brain demand accurate determination of whether and how CB2 receptors are involved in the cognitive effects of cannabinoids.

CB2 cannabinoid receptors are primarily involved in immune functions, but also implicated in psychiatric disorders such as schizophrenia and depression. Here, we examined the effects of CB2 receptor knockout in mice on memory to determine the roles of CB2 receptors in modulating cognitive function.

Our results suggest that CB2 cannabinoid receptors play diverse roles in regulating memory depending on memory types and/or brain areas.”